Thursday, April 24, 2014

Travel Hacks : Bird Festivals

In high school I spent a lot of time birding in groups
like this one, I'm in the red hat, OYBC Field Trip 2006

One of the wonderful things about traveling is that there are new birds to see. It can also be a little overwhelming. trying to figure out where to go and what you are likely to see. Bird festivals are one way to get around this problem, visiting a new place during a festival you can take advantage of all the great people there.

Bird festivals are a strange beast, if your a solo birder, like Boone often is, they might sound a bit ridiculous. I grew up with the chaos of the Magee boardwalk in the spring, where claustrophobia and birding go hand in and and I love it. Birding to me at a young age was a group activity and spending time with the people was as  much a part of it as the birds.

If you want to meet people who are just as geeked out over things with feathers as you are bird festivals are fantastic. In addition to meeting many fellow bird loves they are great ways to check out new equipment (scopes and binoculars!) and meet birding celebrities. They can also help improve your birding skills but participating in workshops and field trips led by fantastic guides. Festivals can also be great ways to go birding in a new place. If you've never been to South Texas before knowing where to bird and identifying all the new species can be intimidating. By taking advantage of the bird festival you'll be around many knowledgeable people who can help you have a great time.

What is important when deciding to attend a festival is to do your homework so you pick the festival that best fits what you want. One of the big things to find out before you plan a trip, especially for big festivals, is if there is anywhere near by to stay. For some festivals in remote areas the limited hotel space fills up fast, so plan ahead, or prepare to be flexible. Often by checking out a festivals website you can get a quick feel for the festival and if it will fit your needs. Some festivals are all inclusive, where you are 'expected' to do everything. Others are buffet style, you pick a workshop here, or a field trip there, and can do things at your own pace.
The boardwalk at Magee WILL be packed, much more
then this (Dakota Kingfisher)

Last fall Boone and I were down in South Texas for the Rio Grande Valley Bird Festival. Being cheap we didn't go on any of the field trips (though I hear they are fantastic!). We attended some of the speakers and hung out at the vendors fair. It was a great way for us to get to meet other birders and get to enjoy the atmosphere of the festival, while also having the freedom to go birding as it suited us. You can't take all in a piece meal fashion, though you can find a way to make any of them fit your needs, you just have to do your homework.

My personal favorite festival is The Biggest Week in American Birding, held every May in NW Ohio. I'm a native Ohioan, and I love the marshes of Lake Erie. The Biggest Week is the brainchild of the wonderful people at Black Swamp Bird Observatory (BSBO). It has become a great way of bringing birds and birders to the attention of local communities. BSBO is all about showing local businesses that birders are bringing their money to NW Ohio because of the birds, and using the tourism opportunities to help both our local economy and the birds! (it's pretty awesome)

The Biggest Week is a festival you can definitely piece meal if solo birding is more your style. I should warn you though, true solo birding is going to be challenging because there are SO MANY PEOPLE around searching for birds, but you don't have to go on field trips if you don't want to. There are many workshops, talks and other activities going on though that I would encourage you to check out. They are great ways to expand your skill set and meet some like minded birders.

There are dozens of birds festivals in the U.S. alone every year (and many more in other countries). The database from the American Birding Association lists many of them and helps you get started planning your next big trip. What is great is you can search by both region OR month. So whether you're a student trying to find something over spring break or you want to find something in your home state, you've got the right resources.

Hope to see you at the Biggest Week this year, I'll be there just for a day, but I cannot wait.

- Auriel

Thursday, April 17, 2014

I found a baby bird! What do I do?

Its that time of year again! Across the northern hemisphere birds are raising their young and sometimes their young end up in unexpected places. This infographic from the birdandmoon.com provides a nice flow chart, with a good dash of humor, since not every baby bird you see needs your help.

(Credit to birdandmoon.com)

There is a lot of misinformation out there about baby birds, likely told with the best of intentions. Most people read this infographic and immediately respond 'if I touch a baby bird the parents will abandon the baby, the mom will smell me.'

Birds aren't the best at smelling, (though they can) but there is no evidence picking up a baby bird and putting it back in the nest will cause the parent to abandon it. When you find a bird who is very young (almost no feathers, or eyes closed) then they aren't ready to be on it's own yet and putting it back in its nest will probably help it survive.

If you find a baby bird who can't seem to fly, but has open eyes and lots of feathers, they are a 'bird in training' and while moving them off the sidewalk is probably helpful its important for them to bring on the ground so they can figure out the whole flying thing. Baby birds have a training period where they leave the nest and learn how to fly. This often means they spend a lot of time on the ground since they can't get back up in the tree. Their parents are still around feeding them, and if they seem to be making a lot of racket that's because they are hungry and they want mom and dad to be able to find them. 

It can pull on your heart strings to leave a baby bird sitting under a bush when it appears to be abandoned, but if you take a step back (well probably several steps back) and watch for awhile mom and dad will return. 

There are, of course, circumstances where a young bird does need help, if it has been injured, attacked by a cat, or if you have been watching it for more then a day and no one is feeding it then that bird needs help. If that happens you need to contact a wildlife rehaber. Rehabbers are specially trained to take care of injured birds, and they know what to feed them and how to help them heal. It's very important for baby birds eat the right things. Feeding them whatever you have around the house isn't going to help them and could very well hurt them. Many wildlife rehabers take on volunteers, so if you want to learn more about how to properly care for them, contact your local rehaber.

So do not fear if you find a little ball of feathers as you go about your day, just follow the handy diagram and act accordingly, nature is all around us and having the opportunity to see young animals up close is always special, but not always a reason to get involved. 


- Auriel

Thursday, April 10, 2014

Travel Hacks : How to Start Hiking

Devil's Den State Park, Arkansas
Have you felt intimidated walking into a sporting goods store and seeing all the specialized equipment? All you want to do is go hiking this weekend and now there are a bajillion brightly colored things everywhere. You're not alone if you feel overwhelmed by all the stuff. Lucky for you, don't need any fancy equipment, all you need is some basic knowledge on how to plan your day and what to expect. With a little bit if basic knowledge you can hit the trail this weekend.

Understanding how to plan a day, and most importantly what you are capable of tackling in a given amount of time is important. More than once I've come across a pair of hikers who are in way over their heads. They're four miles from the trail head, didn't bring water, have no idea where they are or what is going on. These kind of experiences can be scary and unpleasant, so it important to have a rough idea of what you can tackle in a day so that you can do what you're going to enjoy.

Before You Go


The big thing that most people don't know is how long it takes to hike, and how far a mile really is. You might go quicker then this, but with stops to enjoy the scenery, taking breaks and such, a half hour a mile is a good rule of thumb. If you are hiking in a fairly flat area, most people can hike several miles no problem, but if there is a lot of elevation change it can become challenging quickly if you aren't used to it. Sometimes pushing yourself this way can be really enjoyable, but if you have small children with you, or aren't ready for it, it can be an unpleasant challenge. So assess your own abilities, hiking can be a great way to get in better shape, but that is a gradual process.

Most trails will have maps online, or at the trail head that give you basic information about how long the trail is, and often a rating of difficulty. Checking out this information beforehand can help you pick a trail that matches your abilities. I prefer taking loop trails so that there is always something new to see and explore. I also like trails that have one or more 'high points' that is designated bits of scenery where you can stop. Often hikes to overlooks, tops of mountains, and waterfalls are set up this way.

Once you are at the trail head and before you head out take a few minutes to familiarize yourself with your surroundings, look at the map, find your place on it and look at where you are going to be hiking. Find out what will mark the trail, often the trail will be clear since it is heavily used, but in some places it may be posts in the ground or marks on trees that show you the way. Its always a good idea to have a map with you, and if there aren't paper ones for you to take, snap a picture on your phone.

What to Bring

This is about all you need to enjoy an afternoon hike. 
What you bring with you on the trail is pretty flexible, except for one thing, ALWAYS BRING WATER. I don't care if its a half mile hike on a paved bike trail, just bring it. Worst case scenario you carry some extra weight and burn an extra calorie or two.

Dressing for the weather is also important, so check the weather before your hike. Wearing layers is often the best idea so you can add/remove them as necessary. Even if the sun is shining bringing a rain coat is always a good idea, they can block the wind and the rain and keep you warm if the weather changes quickly. During the summer make sure to wear sun block, when you're hiking sun burn can creep up on you so be careful. You do NOT need fancy clothes to spend a day out hiking, what you have already is more then sufficient. Wear shoes that give you good footing, like tennis shoes or hiking boots. No flip-flops or loose sandals, they can result in a twisted ankle.Throw on some clothes you don't mind getting dirty, grab a jacket appropriate for the weather, toss your water bottle and a snack in a backpack and you are good to go!

Taking photos of your hike is a great way to help you look more closely at what you see and its a great way to share your adventures with your friends and encourage them to come along next time. So grab your camera or use your phone and document the cool thing you find! 

On The Trail

Many people like planning things to the minute, this is often unrealistic when you are outdoors. Let the day guide you. Hiking is not a competition, and its way more enjoyable to take things at your own pace, be respectful of other hikers and let them pass if they are hiking faster then you. If you find a sunny beach along the trail and want to spend the afternoon there, do it! If it starts to rain and you want to call it an early day, that is fine too.

Hiking is a great, cheap way to get out in the sunshine, stretch your legs and explore a new place. Once you get away from the trail head you never know what you might find,so get out there and explore and come back and tell us what you find!


- Auriel

Thursday, April 3, 2014

Migratory Timing at Cape May, New Jersey. Now with more graphs!


While the Gulf Coast is getting it's first influx of spring migrants, I'm stuck in Delaware, 10 degrees too high in latitude, only one week away from the last snow storm. Instead of being sad, I decided to follow up on my last post and figure out how long it would take for birds to get to me in Delaware and the rest of the north east.

I chose two of the hottest birding spots in the country in spring, Cape May, New Jersey and north west Ohio.

What followed was a frenzy of graph making that borders on overwhelming, so I decided to split this up into two posts. This post we'll focus on Cape May.

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Methods
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Because I already described the methods, I'll keep it short and mention what changes I made this time around. If you want the full methods, check out my previous post.

Because of the delay in timings I chose to take only data from March onward, and then ran it through the same filter to filter out only birds who spent <66% of their time in the area and filter out relative rarities. I also decided to filter out certain species for different portions of the analysis, this hopefully makes things easier to digest.

All in all Cape May had 201 birds identified as migrants and 37 total warbler species. It also had high numbers of checklists each week, which resulted in smooth graphs and trends.
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General Timings
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This graph was the easiest to digest and discern. The overall weighted average turned out to be May 17th, which coincides with this years Cape MAYgration Festival. Unfortunately for me, early April looks pretty bleak, but quickly ramps up and by May migration really takes off.

What surprised me the most about this is the 3 week disparity between the gulf coast and New Jersey. It takes migrants three weeks to go the 1000 miles from Tallahassee to New Jersey. For many species this isn't even close to their end destination. But for many species, New Jersey represents an end point and migrant diversity stayed high for the remainder of the breeding season. I expect this mainly to be the waders, gulls, terns, and shorebirds that nest in the region, as well as many species of orioles, warblers, and tanagers.

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Warbler Timings
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Many birders love spring because of the plethora of colorful warblers migrating through. In all North America hosts 56 species of Warblers and Wood Thrushes. Of those 56, Cape May hosts 66% of all of these species in the entire country. So when do these beauties show up and when is the best time to see them?
Luckily I made very large graphs to help you out.
To save space I used the 4 lettered Alpha Codes for species. You can download a pdf of all the species codes here. I used the first date that a bird was seen with a higher than 1% chance to filter out the extreme individuals and the accidentally overwintering birds. This should represent a conservative if not accurate average estimate of first arrival. We see Palm Warblers and Yellow-Throated Warblers are already expected to have shown up, this is largely to due a couple of years vagrants overwintered in the area. The first Louisiana Waterthrush just showed up in Delaware and New Jersey this week justifying the early timings in the data. After that, birds seem to ramp up over the second and third week in April with the first wave of typical early migrants (Ovenbirds, Prothonotarys, Hoodeds, and Black-Throated Green Warblers. Then curiously there's a large break before the final wave of migrants show up May 1st and the famously late warblers show up (Blackpolls, Black-throated Blue, and Cape May Warblers).  While I've heard of 'waves' of migrants I didn't actually expect it to show up with such a large gap.


To get at when the bulk movements of these warblers were, and if these waves are seen in the bigger picture I graphed the average timings for each species. This came up with a much different graph.
The first thing to notice is that despite some really early timings, all warblers peak in the latter parts of May. While averages are expected to be smoother we can still see certain waves, but now it could be broken up into as many as 5 different groups.
Early- Palm Warblers, Louisiana Waterthrush, Nashville Warbler, Yellow-throated Warbler, and Black-and-White Warbler
Mid-early- Ceruluean Warbler, Black-throated Blue warbler, Northern Parula, Black-throated Green warbler, Cape May Warbler, Northern Waterthrush, and Blue-winged Warbler
Mid- Blackburnian warbler, Chestnut-sided Warbler, Ovenbird, Hooded Warbler, and Prairie Warbler
Mid-late- Tennessee Warbler, Wilsons Warbler, Magnolia Warbler, Worm-eating Warbler, Blackburnian Warbler, Kentucky Warbler
Late- Blackpoll Warbler, Canada Warbler, American Redstart, Prothonotary warbler, Mourning Warbler, Yellow Warbler, Common Yellowthroat, Yellow-breasted Chat

While many of these make sense, the resident warblers are obviously getting pulled farther back than expected. I suspect that's why we see Yellow Warbler, American Redstart, Ovenbird, Prothonotary Warbler, and Yellow-breasted Chat on the back end of these graphs instead of closer to the beginning.

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Family Timings
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At the beginning of this work I was curious in looking at all migrant timings across families to compare when birds migrate across large areas. My first try resulted in the infamous gulf .gif that plotted every family's timing across 4 locations spanning 1500 miles. While I still want to figure out a way to graph broad scale timings like this across multiple locations, I think it's easier to digest each location separately. So I made a graph depicting the timings of 9 families just for Cape May.
 The most surprising part to these graphs is how quickly most of them spike. I expected all of the graphs to turn out like the Warblers and Shorebirds with smooth ramps to the peaks and gradual drop offs. This is most likely due to the large amount of species and numbers incorporated in the Shorebirds and Warblers, where as other groups like Orioles and Cuckoos may have only two species representing them. It mainly shows how concentrated the migration of any one species is, and how in sync each individual is to the timing of a species as a whole. I'll briefly go through each of these families.

The Shorebirds and Warblers peak right around when Cape May's over all numbers peak and then drops off much more suddenly than in April.

The Night Jars and Hummingbirds curiously peak at similar times and have similar graphs. They both peak slightly later than normal around the last week in May

Cuckoos true to their nature show up late and then stay at high rates of detection due to their wonderfully nostalgic and unique call.

Flycatchers are another set of late bloomers that technically peak near June and stay to breed. These include the charismatic Eastern Kingbirds that are hard to miss.

Vireos usually follow the Warblers in timings and despite an abrupt start generally follow the same graph as the warblers. They peak just a day behind the warblers and their tail end graphs look almost identical.

Tanagers, Grosbeaks, Buntings, and Orioles were groups I expected to have similar timings just from anecdotal evidence and I am continually surprised every time I find this trend still showing up in the data. Not only do their averages land on the same day (June 1st) they have almost identical graphs, and both represent strong residential populations after migration.
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That's it for now. Spend the next week staring at these graphs and hopefully learning to make your own. I'll be back April 17th to present the North West Ohio data just in time for the Biggest Week in birding!

So go out, and start looking for migrants!
-Boone

Thursday, March 27, 2014

How to watch migration

Golden-winged Warbler, Minnesota, 2010
Spring 2010 I got hired to travel all over Minnesota and Wisconsin in search of Golden-winged Warblers. That job is how I originally got introduced to eBird.  Every day, starting in April, I checked the Golden-wing map to see if they had arrived in Wisconsin yet. Finals were the last week in April and my crew was set to jump in the vans and head to Wisconsin as soon we finished our exams. We were just waiting for eBird to show us if the birds had arrived, and arrive they did!

Checking eBird every day and watching eagerly for those points to get farther and farther north got me addicted to checking eBird and diving into the immense amount of data eBird has about bird migration.

eBird is a treasure trove of information. Its a great way to learn about a new place and it provides us really neat ways to look at how migration varies from year to year. It also provides you near real-time data so you can see what is going on with migration RIGHT NOW! This makes it an addictive tool, especially in the spring when I am chomping at the bit for all the birds to come back. 

How do you do this? It's quite easy, go over to eBird.org and click on 'explore data', then click on 'range and point maps'. In the upper left hand corner type in the species of your choice. Right now it's mid march, and the Purple Martins are starting to make their way north, so lets take a look at these signs of spring.

So the first time you enter in Purple Martin it's going to show you everywhere a purple martin has every been recorded. Crazy, and a bit overwhelming.

Next to the species slot is one labeled 'Date'. Checking these maps is where migration becomes watchable. Click on the date drop down and select 'current year'. Choosing this option limits the map to just the areas where Purple Martins have been observed during the current calendar year.

So check it out. I'm currently in NW Arkansas and I've been hearing reports of martins on the list serve for awhile. It looks like Purple Martins are just starting to push north of Arkansas. Since the Midwest has been getting regularly hit with snow over the past few weeks this is probably a wise choice on the part of the birds, though it looks like spring might finally be arriving!


By checking out maps like these for a wide variety of species you can watch migration happen and if you check back every day or every few days you can see the line of purple slowly move north and can better expect what might be around your favorite patch.

What is also fun to look at is how the current 'range' of a species compares to other years.

So head back up to the date drop down and change two things. Instead of current year click on 'last 10 years' and change the month range to just march (so March to March, it's weird, i know).

You should see something like this: Which presents a different picture.



Part of the difference between these two images could be because March isn't over yet, and chances are Purple Martins will make it farther north before April 1st. It might also show the difference between this year and the last, so check back at the map at the end of the month.

The big message here is bird distributions vary year to year. By looking at the 10 year image you can see the farther north areas are lighter purple, indicating less sightings. So not every year are Purple Martins back in Minnesota or northern Ohio by the end of March, but some years they are. Boone's post back at the end of February talked about how spring migration can be treacherous for birds, and how they delay their progress north until conditions improve. Birds are in a race against time, trying to make the most of the good summer weather and be the first ones back on the breeding ground. Some years this pans out and they make it farther north by the end of March. Other years, like 2014, winter is sticking around for awhile, and these birds will either hang out farther south and wait or deal with the chilly weather farther north.

Try out other species and see what is headed your way soon! You might be surprised what is hanging out just a few miles south of you waiting for the weather to break. And of course put your own sightings into eBird and help give everyone north of you some hope as well. But most of all get out there and see what is showing up, many species will keep moving north no matter what the weather and you might be surprised what is already around. Spring is coming and the birds right along with it!

- Auriel


Monday, March 24, 2014

How long does a Indigo Bunting live?

Male and Female Indigo Bunting
(Sandusky County Park District)
Getting to hold a bird in your hand is a really special experience. You can feel the birds heat beating, feel how warm it is, look it right in the eye. It gives you a connection with an individual bird you can't experience any other way. Bird banding got me addicted to birds and to research. I got involved when I was young and I'm still addicted to this very hands on method of studying birds. That is why I got so excited when I found out that one of the people who got me into bird banding captured a bird that set a new record for longevity (life span).

Tom Kashmer, bander for the Sandusky County Park District and Black Swamp Bird Observatory captured a Indigo Bunting last fall in NW Ohio that had been banded. He recorded the band number (each bird gets a unique number) and after submitting those records to the bird banding lab he learned this bird is THIRTEEN YEARS OLD. Totally blowing away the previous record for Indigo Buntings (8 years).

All data collected about birds banded in the U.S. is submitted to the Bird Banding Lab, (BBL) which is run by the U.S. Geological Survey. Having a central database allows us to have one resource to go to when we want to ask scientific questions and also allows us to track birds when they are recaptured. Tom did not band the Indigo Bunting originally, Mark Shieldcastle (Research Director, Black Swamp Bird Observatory) did, 13 years earlier, in a different part of NW Ohio. Since those records has been submitted to the BBL when Tom submitted his record of the recapture they were able to pull up the band number and see its entire history.

Mark Shieldcastle (Original Bander) and Tom Kashmer
(Recapture Bander). (Sandusky County Park District)
Most passerines have an expected life span of 2-3 years [2] and for migratory species their lifespan can be even lower. Indigo Buntings migrate to Central America every year [3] so in this birds 13 years it has flown a long way and managed to dodge many of the hazards migratory birds face every year. While this bird is likely an anomaly it is important for us to understand both the 'average' behavior of an Indigo Bunting, but also the behavior of these more extreme birds, the outliers. Many times changes in a species is pushed by outliers. A male who lives for 13 years has probably produced many more offspring then one who only lived three years. This is just one example of the new information we can continue to learn by banding birds. 

Not everyone is such a fan of bird banding[1]. While many of the concerns raised in this article have been addressed there are still many of the concerns about the impact banding has on the individual bird, either because the bird will be injured through the process, or experience stress which will hurt it in some way.

Another concern is since we have been banding birds for so long we don't need to continue doing it, because we are not gaining any new information. Recapture rates for many species are very low (less then 1% for non-game species) [1]. The low rate doesn't prevent us from learning lots of important things about these birds. Banding allows us to understand population ecology, which might sound very abstract, but its extremely important to understand the demographics of a species population and by individually marking birds we are able to do that. It also allows us to look at migratory connectivity, since birds can be recaptured throughout the year. Even when a bird is only captured one time we can still learn valuable information and we can document that birds presence on the landscape in a way that isn't possible through passive observation. When recaptures happen we learn a HUGE amount of information. We can track that bird through time, learn about how it has changed, and also how long it lives.

The documentation of this long-lived Indigo Bunting is a big moment for both birds and scientists. These kind of discoveries can be made by anyone though! If you ever encounter a dead bird, check and see if it has a band on it's leg, and if it does, please report it! Having information about when and where a bird died is extremely useful! If you're in the U.S. you can report banded birds here to USGS.

Citations
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[1] http://www.westernbirdbanding.org/HaltBanding.pdf

[2] http://www.zin.ru/labs/ornithology/payevsky/pdf/06-Payevsky-2000.pdf

[3] http://www.allaboutbirds.org/guide/indigo_bunting/id


Thursday, March 20, 2014

When do birds really migrate?


So what exactly do I do with my little free time in graduate school? Recently it's been playing with Ebird data to do more research. To test the effectiveness of  using Ebird data to answer scientific questions, I decided to answer one problem I've always wanted to know.

When do birds really migrate?

This large scale question seems appropriate for one of the largest bird sightings databases on the planet. The eBird database gains more sightings every year. You can see this rising submission trend in the yearly Top 100 lists. Every year the top 100 becomes harder and harder to break into as more people post their data on Ebird.

This experiment actually turned out quite well and was a great learning experience. The resulting graph above is quite busy but we'll slowly go through it and interpret it for you.

From here you can either read the methods section following, or skip straight to the results.

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Methods
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So how do you get this data and how can you use it? eBirds philosophy is open data access for everyone. You can either ask for ALL the data ever in a raw format, or let eBird do the hard work. I decided the later and downloaded histogram data. This gave me the percentage of lists in my chosen area that saw the specific bird. It's essentially presence data. I downloaded data for all the birding sites in my areas of choice for the last 10 years. Most of these sites were based on migrant birding spots I already knew about. They are as follows:

-South Texas included South Padre Island(including the nature center), Laguna Atascosa NWR, Santa Ana NWR, Boca Chica, Sabal Palms, and some other migrant hot spots

-Upper Texas included all the famous High Island Spots including Smith Oaks, Boy Scout Woods, Bolivar Flats, Sabine Wood, Anahuac, Mcfaddin, and Lafitte.

-Alabama included every site on Dauphin Island and Fort Morgan/Bon Secour

-South Florida included any hotspot that had more than 150 birds seen in it. This was because I've never birded South Florida in spring, and I incorporated a larger area to make up for my lack of knowledge. These included all sites in Everglades NP, Key Largo, and hot spots around and along the coast in Miami including Bill Baggs Cape State Park and Matheson hammock.

These choices resulted in a large mix of wooded, grass lands, and large wetlands across the gulf. They resulted in a large difference in sample size between Alabama and the Upper Texas Coast. With Texas having the highest checklists and amounts of birds seen (400+) over the 5 month time period.

Once I had the data, I manually grouped all the birds into broad categories that vaguely represent Families. While most of these are obvious some should be explained.
  • Waterfowl did not include sea ducks as I thought this muddied my interpretation.
  • Hawks included Eagles and Kites (It really should be labeled raptors)
  • Nightjars are both nighthawks and nightjars
  • Cuckoos-the smallest grouping only included 2 species (Black-billed and Yellow-billed Cuckoo), but I felt it needed to be separated because their famous late timings.
  • Tyrants-include all flycatchers and kingbirds
  • Swallows-also include swifts
  • Small Migrants-This category had to be made to keep my categories to a manageable extent. It includes Warblers, Thrushes, Waterthrushes (In later iterations I will separate these more appropriately)
  • Tan/Gros/Bunt-Just incase no one understands, thats Tanagers/Grosbeaks/Buntings

I then made the tough decision of deciding what was a migrant, and what wasn't. The problem is some species (especially in southern latitudes) are year round residents and so just splitting my categories wasn't enough. South Texas Orioles are a particular good example; there are 2 resident Orioles (Altamire and Audubons), but during spring 7 species of Orioles are seen in the area.

I decided to subset the data based on if a species was sighted during less than 60% of the time period. As I started in February, I thought this would represent only birds who spent a portion of their life in the area. This filtered out effectively all but the rarest of species, most of which I either manually took out.

Now with my base data set, I summed up all presence percentages in a 1 week window and divided by the total percentage through all weeks in Migration (Feb-June). This created a standardized metric that basically shows at what window the group is most likely to be seen between. If a group is only seen during a two week period, it would have a huge spike during those weeks and then no data otherwise. If it's seen consistently through all weeks, the values would be even with no spikes.

I ran all of this in the stats program R (praise be to him).
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Results
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So what the hell is going on here?

A whole hell of a lot. But before we start interpreting let me remind you the variability inherent in data of this kind. This is a conglomeration of thousands of peoples bird lists. They span a vast amount of birding skills, truthfulness, and exactness. Species may be incorrectly identified, effort hours may be off, and birding may not even be reported sometimes. It also has a high degree of variability with birds that are not easy to spot, like rails. If someone is on High Island for migrants, they may not even go looking for the rails, and thats not taking into the fact the incredibly secretive nature of rails. (except on the South Padre Island Nature Center boardwalk)

So with that, we'll move forward and interpret group by group.



Waterfowl (red)
The waterfowl are the easiest pattern to discern. In February they're very common, peaking right at the beginning of our study period. What surprised me was how late waterfowl stayed. I inherently knew this, but it takes until April Week 4 for waterfowl to really be off the radar.

Hawks (orange)
The Hawks followed almost the identical trend of waterfowl, except in South Texas. A famous spot for hawk migration, South Texas hosted more hawks farther into the season. These peaks aren't evident even in the Upper Texas coast, possibly due to the spreading out of these hawk populations after reaching South Texas. It's also interesting to note the presence of so many hawks in winter is due to species like Harriers, Ferruginous Hawks, Osprey, and Sharp-shined Hawks that move their distributions south in Winter.

Rails (yellow)
Auriel and I's favorite group had the craziest of graphs. The interpretation is muddied by a lot of different factors. For one, Rails are difficult to detect, especially in winter, and two not many people look for rails if they're not calling. This means rail detection is a function of calling and to a lesser extent the threshold amount of rails it takes to start seeing them run out in the open. Rail's also winter on the gulf coast and species like Gallinules migrate across the Gulf of Mexico. The graphs seem to show an increase in detections starting April 1st, but then peaks in May. I personally think this is because Rails are infinitely easier to detect when they're calling during breeding season, not because they're migrating late. Clearly better data is needed

Shorebirds (greenish yellow)
Shorebirds show a constant migratory presences starting in mid march, and continue at a steady rate, till they peak again in late May before quickly disappearing. In many cases this could be due to a subset of late migrants. My opinion is this is a subset of arctic breeding migrants that show up much later while they wait for the arctic to warm up.

Gulls/Terns(actual green)
Gulls and terns are constantly present on the southern latitudes. Most terns can be seen in South Texas and South Florida at all times of the year, and all of the coasts get a switching out of various gull species. In the northern sites, we see a sudden spike in presences of gulls starting in the last weeks of May. Whats going on here? Diving into the data a bit more, it seems many tern and gulls were filtered out from screening, leaving only a few species to drive this whole graph. The May spike is driven by the late migrating Franklin Gulls. And then as they move through, the left over breeding terns like Least Terns increase in either abundance or detectability in the upper gulf coast. This is particulary evident comparing Alabama and Florida. In April gulls/terns are common along the coast, but by June they've left the southern latitudes to breed.

Nightjars(some other shade of  green)
Nightjars/Nighthawks are breeders in the south and show up much later than many of the migrants. We see the first presences of them around April Week 2, and then they steadily ramp up till they're at their peak in June. This is a function of the fact a lot of these nightjars will breed in the south and are really conspicuous due to their breeding calls and evening flights.

Cuckoos (bluish green)
Like expected, Cuckoo abundance spikes much later than the passerine migrants. The peak seems to be between the 1st week in May. Once cuckoos arrive they are commonly found. This is most likely due to their obvious call that can be heard from far away in riparian corridors. While this group only contains 2 species, I was surprised it created such a nice clean graph.

Hummingbirds (teal)
Hummingbirds winter in the southern latitudes, especially in South Texas and Florida. This creates a great dichotomy of hummingbird abundance starting in the beginning of April. At that point all the hummingbirds in southern latitudes disappear and abruptly appear on the northern Gulf Coastl. Then ny June all of the hummingbirds have migrated out of the area, and few migratory hummingbirds remain in the area.

Aside from Sparrows the remaining groups are common passerine migrants that show similar timings.

Tyrants (white)
Tyrants start moving through a little earlier than the small migrants and then stay at a higher proportion than the smaller migrants. I expected this from the high amount of tyrants that breed in the south especially Texas (Scissortailed Flycatcher, Eastern/Western Kingbirds, Acadian Flycatchers, Vermillion Flycathcers, Great Crested, Brown, and Ash-throated Flycatcher). Though in general, the tyrants maintain a presence at all southern latitudes throughout the year.

Vireos (light blue)
Vireos moved in a very sterotypical pattern, they ramped up migration starting in Week 3 in March, they peak Week 2-3 in April, and leave by June 1st.

Swallows (Blue)
The swallows appear to already be on the move once February hits, but they really start migration mid March. Once May hits, swallow numbers dive quickly and are gone by mid May.

Small Migrants (Blueish Purple)
The small migrants represent the largest group by numbers of migrants. They category in itself is a bit disingenuous because many of these small migrants winter on the gulf coast. Certain warblers like Parulas and Yellow-throated Warblers winter in South Texas and Florida, and Hermit Thrushes are uncommonly seen at all our sites in the winter. The popularity of warblers, plus their mass numbers helped give this category the smoothest graph. In general, small migrants began migrating late march, peaked Week 3 in April and tapered off by June.

Sparrows (purple)
The sparrow are a common winter resident all around the country. They stick around till the 1st week in April, and as the gulf migrants start to peak, the sparrows decline and are gone by May 1st.

Tanagers/Grosbeaks/Buntings (pink)
This was another small group that showed up well in the graph. This group had a large spike starting the first week in April and then gently tapered off till the last week in May. We can really see how concentrated some of these movements are within Passerines. Neither Tanagers, grosbeaks, or buntings are particularly related to each other. Grosbeaks are a mixture of multiple families and buntings are in the family with sparrows. Regardless of their real lineage most Passerines are migrating in this small 6 week window

Orioles (fuschia)
This was the second smallest group, and contained the largest spike in presence. All the Orioles migrate during a concentrated 5 week window between Week 1 in April and Week 1 in May.  The interesting thing is the continuing presence of Orioles in the High Island area in June. This is due solely to the amount of Orchard Orioles that nest in the area.

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Overall Timings
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So we've successfully mapped all the migrants, and I've got you all excited for migration. You may even be thinking of planning a trip down to these spots. But when should you go???

Well I've got you covered again.

I took all the presence data across each one week window and summed them to quantify the general diversity at each time frame. I then took the weighted average across weeks to find the center of the data where the highest diversity and numbers of birds could be seen. The weighted average is just the value seen multiplied by the probability, so in this case the proportion of sightings in that week compared to all 5 months. I then plotted each graph to visualize timings. The way the numbers work the Y axis is largely meaningless. Just focus on heights relative to each other.
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South Texas

  
South Texas had a beautiful graph with highest diversity the last week of April. It sharply spikes in April and is most productive during Week 2 in April and Week 3 in May, making up a 6 week window of great birding. The weighted average landed on April 19th. This is only a couple days shy of Week 4 in April. The sharp spike in migrants is largely due to the fact that most birds are residents of South Texas, birding is always good from Winter to Summer, so what we're seeing in this graph is the filtering out of all these resident birds, and we're left with just migrants.

Upper Texas Coast
High Island approaches what we call a normal distribution, with a positive bias due to the breeding migrants in the area. The largest spike occurs in Week 4 in April, and this shows in the weighted average falling on April 24th. This is actually inline with a typical Big Day, and only 1 day off from Team Sapsuckers record breaking big day last year on April 25th.

Alabama
The problem with Alabama's data is definitely a sample size problem. Without enough samples the graph bows out without centering on a specific point. This could be due to the fact Alabama actually receives some of the lowest number of migrants due to prevailing winds blowing north west in spring. The mean track of birds tends to funnel between between Louisiana and Texas. For major fallout events in Alabama to occur winds have to unpredictably shift east. This might lead to the spreading out of peak abundances across April. On the graph, the highest peak occurs Week 1 in May but the weighted Average actually sits at April 19th.

South Florida
South Florida isn't necessarily known as a migrant hot spot in Spring. Many birds cross the gulf of Mexico instead of moving along the over land route in Florida. Radar studies show very little use in Florida, as many birds skip over southern Florida entirely, landing around Tallahassee instead. South Florida is also the first stop for migrants in the Caribbean, as opposed to birds traveling from Central America that land in South Texas after crossing the gulf. This means we'd expect to see an earlier peak of migrants. Finally, a lot of bird species winter in South Florida, but very few migrants end up breeding in South Florida, this skews the graph negatively towards the earlier weeks. All of this leads to the graph showing a peak in Week 3 of April but the weighted average being pulled all the way to the April 8th due to the lack of migrants in May and June.
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Many weeks and almost 3000 words later, I've still only touched half of what this data set tells us. I'll be using Ebird in part of my Masters Thesis now, so I plan on testing more methods on the blog as I can moving forward. Stay tuned! And get excited! Spring is here! ...sort of...

-Boone

Thursday, March 13, 2014

Insect Migration - It's a Family Affair

Monarch Butterflies in a fir tree (pendens proditor)
I'm in the process of studying for my comprehensive exams. Without going into detail 'comps' is the biggest test of a PhD students life and I've been tasked with learning 'ALL THE THINGS' about migration, among other topics.

I'm trying to read as broadly as possible about migration and not just focus on my favorite taxa, birds. Lately I've been reading many many pages about insects and noticed that there are some remarkable parts to insect migration we just don't see in other species.

One BIG difference between bird migration and insect migration is often insect migration is multi-generation. Which means that it takes several generations to make the complete circle of migration.

A prime example of multi-generation migration is the monarch butterfly. Monarchs winter, primarily in Mexico, in huge groups where they cover the fir trees. In the spring they start to move north. Each generation moves a bit farther, lays eggs and then dies, then their young hatch, grow to adulthood, migrate a bit farther and the process repeats until they reach the northern extent of their breeding range (see map). In late summer a special generation of butterflies is born, these will migrate hundreds of miles back to Mexico, all in one big movement. These individuals overwinter in Mexico and then start the process back north the next spring.

North American Monarch Butterfly Range. (Journey North)
Migrating through several generations is remarkable for several reasons, the biggest one is that each individual insect doesn't get a chance to learn from the previous generation or have any room for trial and error. One of the big things we look at in bird migration is how the bird navigate, how do they know where to go year after year? Some species are well documented to teach their young where to go, others head out on their own seemingly programmed with the knowledge they need. Often young birds end up in odd places, but the idea is they learn and the next year they are  better prepared for migration.

Insects don't get to take advantage of trial and error during migration. Monarch Butterflies live for only a few weeks and they have never been where they are going. This is their only shot.

Another remarkable thing about migratory insects is there are often differences between generations of a species if one generation is migratory and the next is not. Migratory individuals will have longer more developed wings. Both grasshoppers and locusts have different phenotypes for migratory and non migratory individuals [1]. Change in body shape between generations is remarkable because there is something happening at the genetic level deciding whether or not an individual will be part of the migratory generation. These patterns are well suited to predictable weather environments. For example, if we had an early cold snap in the fall, a non-migratory individual would be ill prepared to south.

Insect migration has been found to be highly influenced by weather patterns. Large scale wind systems, such as prevailing wind systems and fronts move large numbers of insects. Studies show insects are very selected for the wind direction, only leaving on nights when winds are very precisely in the right direction. Following weather patterns makes sense because insects can be easily pushed by the wind. We have a less clear understanding of how smalls scale weather patterns impact insect migration [2].

Tagging a Monarch Butterfly (Anna Barnett)
Like birds there are groups of insects who migrate during the day, and others who migrate at night. Diurnal (daytime) migrants seem to use the sun, or if the sun is obscured, polarized light to navigate [3]. Nocturnal (night) migrants navigation is not well studied, but it could be magnetic [4].

There are many methods used to study the migration of insects, from specialized analysis of radar data [5] to applying tiny numbered stickers to butterflies wings on the breeding grounds (during the late summer) and recapturing them on the wintering grounds. By having monarchs tagged all across the country we are able to track Monarchs across North America and understand how populations from different parts of the U.S. move [6].

The most impressive feat of insect migration I've found is the migration of  dragonflies across the Indian Ocean. This round trip flight across the Indian Ocean spans over 14-18 thousand kilometers (8500-11000 miles) [7,8] While assisted by wind, it is still quite impressive. They, like the monarchs take several generations to make their huge journey.

Monarch Butterflies, like many other organisms will start migrating soon. While birds will migrate fairly quickly, just taking a few weeks to make the journey north, butterflies will slowly make their multi-generational way north, moving a few hundred miles and laying the eggs of the next generation. They won't be arriving in the mid latitude states until mid May and the upper Midwest by mid June. If you see Monarchs around your neighborhood this spring, report them here and help us better understand how these remarkable critters are moving across the continent. Spring will get here eventually, so keep your eyes peeled!

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On a non-migration related note, today I read about hornets and how they defend their hives from other insect invaders by surrounding the invader and vibrating their thoraxes to create so much heat that the intruder DIES! Nature is so cool sometimes.

- Auriel

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Citations

[1] Denno, R.F. (1994) The evolution of dispersal polymorphism in insects: the influence of habitats, host plants and mates. Researches on Population Ecology 36, 127–135.

[2] http://www.annualreviews.org/doi/pdf/10.1146/annurev.en.33.010188.001151

[3] Hyatt, M. (1993) The use of sky polarization for migratory orientation by monarch butterflies. PhD thesis, University of Pittsburgh, Pittsburgh, Pennsylvania.

[4] Baker, R.R. (1987) Integrated use of moon and magnetic compasses by the heart-and-dart moth, Agrotis exclamationis. Animal Behaviour 35, 94–101.

[5] http://bioscience.oxfordjournals.org/content/53/5/503.short

[6] http://monarchwatch.org/tagmig/fallmap.htm

[7] Anderson, RC (2009). "Do dragonflies migrate across the western Indian Ocean?".Journal of Tropical Ecology 25: 347–348.

[8] http://news.bbc.co.uk/earth/hi/earth_news/newsid_8149000/8149714.stm

Thursday, February 27, 2014

Migration - in all its flavors

Sandhill Cranes Migrating (Serge Melki)
Migration is one of the wonders of the natural world. Millions of animals move thousands of miles every year in an attempt to produce as many offspring as possible. When most people think of migration they think of Canada geese flying south for the winter and their return in the spring. You might not realize, that while these birds demonstrate impressive feats of migration, there are others kinds of migration in the bird world.

What makes all these things migration is they involve going back and forth between two places. It doesn't matter if its 2000 miles south or 3 miles up a mountain.  No matter the difference, birds are always migrating in some way during the year.

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'Loop' Migration
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Loop migration is what you'd normally call migration, where birds arrive in the spring and leave in the fall. Loop migration can be broken down further into a few categories, long distance, medium and short distance migration. All of these are annual movements for the same purpose. Birds migrate to take advantage of seasonally abundant food. In northern latitudes insect populations, fruit and seeds BOOM in a huge way in the summer. Taking advantage of these resources allows birds to produce more young than they would have in the tropics. Northern latitudes also provide an advantage because the tropics have constant competition for resources and higher predation.

Migration is not without it's risks of course but if you reproduce enough it offsets the high risk of dying during migration. In this way, you and the rest of your species can continue into the future, so you win. 

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Altitudinal Migration
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Unless you are lucky enough to live in the mountains, birds migrating up and down in elevation is the kind of migration you are probably least familiar with. Many mountain species take advantage of the perks of loop migration without traveling as far. Altitudinal migration presents unique challenges like extreme weather and changes in snow pack.

Altitudinal migration is quite common in tropical areas, where moving up and down in elevation can help mitigate the impacts of the rainy or dry season on food supplies. By moving around the landscape a bird can take advantage of the habitats with the most food and increase their chance of survival. Birds who live on small remote islands also demonstrate altitudinal migration. Instead of migrating several thousand miles to the next land mass they move up and down the mountain throughout the year. They are likely migrating up and down in response to the annual wet/dry cycle on the island.

Altitudinal migration is unique since its not always done just for the purposes of breeding. Some species migrate up in elevation to take advantage of seasonal abundances of insects so they have plenty of energy to molt their new feathers quickly [1]. It is extremely expensive energetically, which means it takes lots of food and energy to accomplish. Birds feathers go through extensive wear in a years time; replacing them is important for keeping the bird the correct temperature and flying efficiently.

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Irruptive Migration
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Irruptive migration is an odd kind of migration because it doesn't fit the way most people think of bird movements. Irruptive migration doesn't  happen every year, instead they are normally triggered by an abundance or shortage of  food. When food is scarce in the north birds come south looking for other resources; this is often why crossbills irrupt. When food is abundant, such as a boom of lemmings, birds are able to produce large numbers of offspring. A boom in the lemming population is what we think is going with Snowy Owls this winter. Boone did a post awhile back that covers their irruption in more detail. 


American Redstart (Derek Bakken)
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Differential Migration
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Differential migration can happen in every kind of migration. It means a subset of bird populations migrate differently. When males and females migrate separately and winter in different places, or when juvenile birds go south their first year and don't return north for several seasons, they are both demonstrating differential migration.

For example, female Cooper's hawks migrate significantly earlier then males. Arriving earlier may allow them to take advantage of extensive resources and put on weight in preparation for egg laying or to find the best nesting locations [2]. American Redstarts males and females migrate to different areas for the winter [3]. This segregation is caused by behavioral dominance by the older males who set up territories and force other individuals (usually female) into less desirable habitats. The exact reason for most differential migration is still unknown, but understanding the different ways a population migrates help us to better conserve their habitats
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It bears mentioning birds are not the only group of animals who migrate. We'll try and round up a post on those as well here sometime soon. In the meantime, keep on the look out for signs of spring migration near you! SPRING IS COMING!

- Auriel

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Citations

[1] Rohwer, V. G., S. Rohwer, and J. H. Barry. 2008. Molt scheduling of western Neotropical migrants and up-slope movement of Cassin’s Vireo. Condor 110: 365-370.

[2] Hull, J.M. Pitzer, S., Fish, A.M., Ernest, H.B., and Hull A.C. 2012 Differential Migration in Five Species of Raptors in Central Coastal California. Journal of Raptor Research 46(1):50-56. http://www.bioone.org/doi/abs/10.3356/JRR-10-116.1


[3] Marra, P.P, Homles, R.T. 2001. Consequencces of Dominance-Mediated Habitat Segregation in American Redstarts During the Non-Breeding Season. The Auk. 118(1):92-104. 
http://www.bioone.org/doi/abs/10.1642/0004-8038(2001)118%5B0092:CODMHS%5D2.0.CO%3B2

Thursday, February 20, 2014

Why Migratory Birds Ignore Puxsutawney Phil

I for one am tired of the cold. Don't get me wrong, this winter in Delaware has been great. We've had an abundance of snow and few days of freezing rain, but this Texans had enough. I was raised on a steady diet of 6 months of hot, 2 months of cold, and 4 months that are only kind of hot. By mid February it's time to start buying swimsuits and stocking up on suntan lotion.

Punxsutawney Phil the Perpetrator
  (Alessandro M.)
Unfortunately, I don't live in Texas anymore. Punxsutawney Phil, the infallible weather muse, has predicted six more weeks of winter for the east coast. We'll forget for a second that our rodent friend is less than stellar at prediction and take his words at furry face value.

Just 2 weeks from now, the lucky residents in Texas will herald their first of the season main land migrants, and in 3 weeks every gulf state from Texas to Florida will see their very first migratory species. This may sound early to some of you, and indeed it is, but certain individuals in a population will try to get an early start to their breeding season. These include the southern breeding species like the Golden-cheeked Warbler, southern U.S wintering warblers like the Northern Parula , the early gulf migrant Louisiana Waterthrush, and the seemingly always migrating Purple Martin.


This winter has been brutally cold. We've seen record snowfalls in the south, and the great lakes ice coverage at it's highest extent since 1994 (90%). If this years weather and our furry friends ominous prediction is right, these early birds will be in a heap of trouble. So why would an individual migrate early when its still cold and how do birds cope with the wildly inconsistent weather in spring?

The extent of the ice on the great lakes this year (noaa.gov)
Lets start of first with an easy question:
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Why even show up early?
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Birds benefit from arriving early in a variety of ways. They get the best pick of territories, avoid predators, and have more chances to succeeded. All of this equates to better breeding success (the chance of successfully raising chicks to adulthood).

Males arriving to a breeding site first get the best pick of territories. If these males choose the highest quality habitat, they'll have an easier time feeding their nestlings. This increases not only an individual chicks chance of surviving, but increases the numbers of chicks a pair can raise.

Common predators for nesting songbirds include snakes and raptors (birds of prey). The time of the highest nest predation coincides with the middle of the breeding season. Nesting hawks have to forage more as their own nestlings grow up. This increases predation as the seasons progresses. With the progression of seasons, temperatures heat up, leading to more snake species migrating out of their winter dens. This all culminates in peak nest predation in the middle of the breeding season. Earlier migrants can skip this dangerous phase by nesting earlier before these factors peak.

Most songbirds nest multiple times in a season until they finally succeed. Some crazier birds may even renest after they've succeeded in raising the first nest.  In the case of Willow Flycatchers, some parents begin nesting before the first brood is even able to fly! So, with an early start to the breeding season, you get not only more chances to succeed, but more time to raise even more young!

It's clear, there's a real advantage to showing up as early as you can.
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What could possibly go wrong?
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Well mainly weather.
The top weather-related killer of birds is the cold. Untimely snow storms routinely kill birds who aren't prepared. Particularly wet snow can quickly saturate a birds feathers, forcing it to land freezing and wet. Situations like this kill even hardy snow birds. It's no surprise that species who aren't used to cold temperatures regularly die of exposure when an unseasonal cold front penetrates into the south [1].

Ice can also be particularly tricky for birds. Waterbirds, like ducks, require open water to feed. When all available water is frozen over, many starve before they can find water. Because of this, ducks often fly hundreds of miles south in search of open water in the winter. This permanent relocation leaves many of us in the Northern States (yah I just said that Auriel) with a lack of ducks for the rest of winter.

Surf Scoters, Indian River inlet, DE
Birds who usually experience extreme weather are well adapted to it. It's when temperate birds run into this weather that there becomes a problem. These birds spend the majority of their time in warmer locations and tremendous amounts of energy flying thousands of miles north to breed. These exhausted tropical vacationers are ill suited in maintaining their internal temperatures. In spring, spending a night below 10 degrees Celsius (50F) costs a songbird the same energy as flying for 3 hours. [2]. To a small song bird that's ~90 miles! [3].

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So what keeps them from showing up early?
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The range map of Golden-Winged Warblers
Migratory birds react strongly to temperature. The correlation between the average temperature at a migrants wintering grounds and summer grounds is both fascinating and complicated (We'll go indepth on this at a later date). Many studies have shown some species won't migrate north unless it's certain temperature.[2][4] Unseasonably cold temperatures in spring are usually brought about by a cold front from the north. This all but guarantees the northern latitudes are also cold. Migrants can dictate their future weather patterns by monitoring temperatures and delaying their departure till situations improve.

The pattern of migration is generally where southern migrants move through first and northern populations arrive later.  This keeps migrating birds at a manageable latitude, but can lead to highly incongruous breeding seasons. A warbler breeding in the southern Appalachian Mountains in late April has entire month head start over it's twin breeding all the way in Canada in June.


Despite evolutionary traits, some birds still fly straight into bad weather.

Last year, a late arctic blast ran straight through the Midwest. Migrating rails, already on their journey, were faced with frozen wetlands with no where to go. Lucky for them, these hardy wetlands species have adaptations to survive in conditions similar to this. Rail species like the Virginia and Clapper rail are routinely found all the way into Delaware and New Jersey in winter. The northern most breeding rail, the Yellow Rail, breeds just shy of the arctic circle. Their bigger bodies, water resistant feathers, and terrestrial foraging allows them flexibility when it comes to surviving temporarily in variable temperatures.

Two Clapper Rails taking the ice in Delaware raily well
If a birds particular tolerance or adaptations fail, we unfortunately find large scale mortalities.  In March 1904, an estimated 1.5 million birds were found dead buried in the ice and snow after a blizzard in Minnesota. In 1964, 100,000 king eiders died when water ways refroze in the spring. This impact can sometimes be quite extreme on populations. A study populations of cliff swallows in the great plains, lost 54% of their population when unseasonable weather hit the region in 1996 [1].

This extreme consequence acts as a natural checks and balances system for  birds. Nature maintains a hard line that punishes birds that arrive at the wrong time.  Without it, birds would casually move their timing earlier and earlier.

Interestingly, we're actually seeing migratory timings shifting earlier in the spring. Over all global warming trends have lead to earlier plant blooming and migratory bird timing. We're seeing not only earlier migrants but northern range expansions of sub-tropical species into the north. Clearly the cold hasn't stopped them. [5][6].

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Migratory timing is a large field in science, and this article has just touched the tip of the iceberg. We haven't for example mentioned birds being tied to high concentrations of bug activity, or the consequences of freak storms (hurricanes and tornadoes) on migrating birds (my masters research ;)). Clearly there's a lot for us to get to and always more to learn.

If you have any questions or would like to suggest a topic we cover, feel free to email us at naturalausterity@gmail.com

-Boone
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[1]Newton, I. (2007). Weather-related mass-mortality events in migrants. Ibis, 149(3), 453–467. doi:10.1111/j.1474-919X.2007.00704.x
[2]Wikelski, M., & Tarlow, E. M. (2003). Costs of migration in free-flying songbirds. Nature, 423(June), 2003.
[3]Alerstam, T., Chapman, J. W., B├Ąckman, J., Smith, A. D., Karlsson, H., Nilsson, C., … Hill, J. K. (2011). Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds. Proceedings. Biological Sciences / The Royal Society, 278(1721), 3074–80. doi:10.1098/rspb.2011.0058
[4]Gauthreaux, S. A. (1991). The Flight Behavior of Migrating Birds in Changing Wind Fields : Radar and Visual Analyses. American Zoologist, 31(1), 187–204.
[5]Gordo, O. (2007). Why are bird migration dates shifting? A review of weather and climate effects on avian migratory phenology. Climate Research, 35, 37–58. doi:10.3354/cr00713
[6]Marra, P. P., Francis, C. M., Mulvihill, R. S., & Moore, F. R. (2005). The influence of climate on the timing and rate of spring bird migration. Oecologia, 142(2), 307–15. doi:10.1007/s00442-004-1725-x