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.

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.
General Timings
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.

Warbler Timings
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.

Family Timings
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.
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!

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