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 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.




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.


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).
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.

Overall Timings
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.
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.

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.
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...


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!


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


[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.


[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.



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