August - October 2012
Of all the environmental factors that influence migration, perhaps wind is the most important. And this year, more than most it was our biggest frenemy.
How is wind important? Hawks soar using thermals (warm air rising from heated land masses) or ridges (wind pushed up by ridges). Songbirds on the other hand, migrate at night and fly when the winds are light or are in the direction they are heading (when they literally have a tail wind). Because low pressure systems spin counter-clockwise fall migrants will move after a low front passes in the fall or before a low front arrives in the spring. We like to use Hint.fm wind maps to help predict when and where migrants can move. Besides being informative, these maps show the beautiful complexity of wind patterns.
You might now be wondering how we use these maps. Let's use Sept 19th as an example. At 1pm EST there are light, southerly winds along the eastern seaboard and throughout the Southeast. There are also strong southerly winds in the western part of the Midwest. If you imagine that these patterns will slowly move eastward (say half an inch by sunset) you might predict strong migration for the eastern seaboard, the southeast, and the Midwest.
If you made such a prediction you would be right, but you don't have to take our word for it. It turns out that birds taking off and migrating at night are picked up on radar. Here's a radar loop from 5pm EST Sept 19th to 1:40am EST Sept 20th. At the very beginning you can see storm systems across Wisconsin and Iowa. As the frames progress you can see intense circular “clouds” appearing across the east, Southeast, and Midwest. These “clouds” are millions of birds taking off after sunset and continuing to migrate throughout the night. They're circular because they are centered around each radar. We call these appearances "blooms" because they blossom around the radar sites.
Notice that where the storm system is and several hundred miles to the east (about an inch) there aren't any blooms. That's because this is the area which is experiencing strong northerly winds. Rather than fighting the headwind, birds in this area are staying put until more favorable winds come through. The winds along the gulf appear to be favorable for a trans-gulf crossing and you can see the clouds of birds take off and begin to move off the gulf coast shoreline (especially Texas). Looking at the longer loop from 3pm EST the 19th to 2pm EST the 20th you can also see birds taking off in Illinois and Iowa after the front has passed through.
The last piece of the puzzle is seeing how the winds and migration (told by radar patterns) match up with capture rates here at Powdermill. Looking back at the wind map again for the 19th, it looks as though we experienced light westerly winds gradually switching to northerly winds as the night progressed (imagining the weather patterns marching eastward).
The radar shows a level of migration consistent with the local wind patterns, light to moderate migration in western PA and perhaps more importantly, light to moderate around Cleveland OH and Buffalo NY (where birds would be coming from). The day of the 20th ended up being a decent but uninspiring day with 31 species, 100 newly banded birds, and 35 recaptures. The most commonly captured species were Swainson's Thrushes (30), Grey Catbirds (25), and Magnolia Warblers (15).
The next day (Sept 21st) ended up being better with 41 species, 117 new captures, and 40 recaptures despite the fact that it looks as though there was very little migration in our area based on the radar. Speaking with Bob Lieberman who started this banding station 51 years ago and banded here for more than 40 of them, it seems that often there is a day delay between when birds migrate and when we catch them here it Powdermill. It may be that birds first settle into other habitats (on top of the ridges?) and later make their way to our area, early successional habitat in the valley between two ridges. Finally, the next day (Sept 22nd) was not favorable for migration to the north and west of us and our capture rates reflected that (58 new, 35 recaptures).
By now your head might be swimming with images of wind patterns and radars, we know ours is. We cannot truly predict when and where a fallout might happen, only when weather patterns appear to be favorable or unfavorable for migration across broader geographic scales. We are left with many questions, like how do migrants use the landscape at smaller scales? How to they decide where to move to or from and how far? And how will changing weather patterns (e.g. climate change) influence how and when birds migrate? Researchers, including us, have started to look at these questions but as of yet do not have all the answers. It’s the surprise and mystery associated with migration that makes it so exciting. A box of chocolates. A wilderness full of birds. You never know what you’re going to get.
So why was wind our frenemy this year more than most? There were many nights in both the spring and fall where wind was not favorable for migration in our area. Both May and October were comparatively slow. This year we banded 2501 birds in October compared to 3389 in 2010 and 3506 in 2011. Watching the radars we noticed that there were large numbers of birds taking off to the west or east us but often not where we were. Through our recaptures we saw the birds that were here fatten up and eventually (when migration was favorable), take off en-mass. Our capture rates for many warbler species were lower in comparison to 2010 and 2011, including Black-throated Blue (30 vs. 118), Black-throated Green (40 vs. 100), Cape May (18 vs. 65), Chestnut-sided (35 vs. 80), and Nashville Warbler (50 vs. 101). We also caught fewer Ruby-crowned Kinglets (160 vs. 236) and Red-eyed Vireos (95 vs. 173) . On the other hand, with all the strange weather patterns, fronts, winds, and hurricanes (enter Sandy) we did get to see and catch some pretty amazing birds (hello Parasitic Jaeger). And this year, we had some mighty fine chocolate in our nets.
Undoubtedly one of the best captures of the Fall flew into our net on September 29th when we captured this hatching-year Nelson's Sparrow (formerly Nelson's Sharp-tailed Sparrow). This was only the second Nelson's Sparrow ever banded at Powdermill in our 51 years of banding; the first was banded twelve years ago on 09/30/2000.
A few weeks later on October 4th, we had another species rarely caught at Powdermill- this hatching-year Sedge Wren. This bird was the 5th of this species ever banded at PARC, and the first one in 36 years, the last one having been banded on 9/29/76.
And of course, we couldn't do the highlights page without spotlighting a few of the vibrant warblers that brightened our nets this Fall, such as this handsome adult male Blue-winged Warbler, one of 11 of this species caught this season.
An even 'better' catch, this hatching-year male Golden-winged Warbler, caught on August 31st, was the only one of this species caught all year at this station.
It's hard to resist snapping a picture of the striking Black-throated Blue Warbler; the adult male seen here is one of 30 we banded throughout the Fall.
A Black-throated Green Warbler, one of 39 that were banded here this Fall.
A Northern Parula is always a nice surprise in the net, and this hatching-year individual was particularly surprising as it showed up at Powdermill on November 4th, well after most warblers had migrated passed us.
Although never a very common capture at Powdermill this species was almost missed this Fall; we only caught two Northern Parulas this year, compared with 10 last year and 12 in 2010.
Another species not commonly encountered in the net (although they noisily swoop low over our ponds quite regularly) is the Belted Kingfisher. We were excited to band this individual on September 9th.
Although they are also an usual capture for us, we managed to band three Green Herons this Fall, all hatching-year birds.
A Wilson's Snipe, which was banded on November 6th.
One of two juvenile Sharp-shinned Hawks banded this Fall, showing the prominent vertical brown streaks of the juvenal plumage.
Close-up of the Sharp-shinned Hawk's juvenal yellow eye, which will darken to a red color as it matures.
In addition to our 'day job,' we occasionally get to do some nocturnal banding as well. Seen here, banding assistant Heather Kraus carefully bands a Northern Saw-whet Owl as Luke DeGroote, banding coordinator examines another Saw-whet in the background.
When these three owls were brought back from one net check, the crew couldn't help snapping a picture of them all, and named them Decaf, Regular and Espresso.
Once the owls are released from the lab, they often perch nearby for a short time while their eyes adjust to the darkness, offering us one more opportunity to photograph these handsome birds.
In addition to the 10 Northern Saw-whet owls banded, we also banded this beautiful rufous morph Eastern Screech Owl on November 24th.
Although an irruptive species that we can completely miss some years (as we did last year, catching 0 in 2011), Pine Siskins were around in good numbers this Fall. This individual is one of 326 that we banded this Fall.
A flock of Pine Siskins under the feeders near the lab.
We don't very often get side-by-side comparisons to photograph, so we try to remember to take advantage of these opportunities when they arise, such as when we had these two woodpeckers in the lab at the same time.
Seen together, the size difference is obvious between this male Hairy Woodpecker on the left and the female Downy Woodpecker on the right.
Comparison of the eye color in the Brown Thrasher adult (left) and that of a hatching year bird (right).
The Powdermill Avian Research Fall Crew 2012
[Standing, L-R]: Ashley Daniels, flight tunnel technician; Heather Kraus and Blaine Carnes, seasonal banding assistants; Mary Shidel, banding assistant;
[Kneeling, L-R]: Amy Tegeler, Bioacoustics Manager; Brandon Miller, seasonal banding assistant, and Luke DeGroote, Banding Coordinator.
An Advanced Bander Training Workshop was held at Powdermill September 11-16. We were able to double the workshop size this year with the help of Drew Vitz, the previous Banding Coordinator at PARC. Drew is now the Massachusetts State Ornithologist, but was able to return as a visiting instructor for the week.
Seen at left, the Workshop participants and the Fall Banding lab staff with Drew (kneeling, second from left) and current Banding Coordinator, Luke DeGroote (standing, third from the right).
A Red-spotted Newt, a common Powdermill resident that we have to watch for as we check nets (to avoid stepping upon!), especially after a rain.
A Red-backed Salamander found by Ashley Daniels.
As the Fall season progresses, we are often confronted with cold mornings and frosted nets like the one seen here. While it makes a beautiful picture, a morning like this decreases our capture rates as the nets become more visible to the birds, and we know it is only a matter of time until most of our nets will be packed away for the winter season when we operate only a few nets just two or three days per week.
All in all, the crew gives a 'thumbs up' to the Fall of 2012, another season filled with cool birds, unexpected rarities and long days of camaraderie in the lab.
Many thanks to the volunteers that helped us this season: Gigi Gerben, Clint Knupp, Chris Sheedy, Luke Kaspar Gerben, Joe Schreiber and Pam Curtin.