Tuesday, November 9, 2010

Look at the Hawk Watchers, Too! Not Just the Hawks.

October 29 I was hawk watching at Lighthouse Point, in New Haven, Connecticut, one of the best hawk watch sites in New England. The day was not what I had expected; the winds were far weaker than forecast and the count was only a little over 100 by early afternoon, but with a good mix, highlighted by a Peregrine perched for an hour and an immature Bald Eagle that spent some time soaring over us, trying to determine what it wanted to do.

Activity was slowing in the early afternoon, when I believe Lynn James said she had a large hawk out front. Lynn, who has incredible distance vision, said the bird was in a large gray cloud above a blue slit in heavy cloud cover. Everyone scanned for the bird and gradually we found it. People remained glued to their scopes as the bird was way out and still quite small, but acting like a very large bird. Someone had earlier remarked that the site had not had a Golden Eagle yet this season, so it was about time, though it was clearly not typical “Golden” weather.

I got on the bird fairly quickly and soon felt very good about it. It had a Red-tailed Hawk kind of dihedral, visible at great distance. The bird was quite large but gliding straight toward us without apparently moving a muscle or a wing, so we couldn’t pick up any contrast on it, much less a head/tail ratio. I think everyone was thinking “golden,” but just could not see enough to call it. As the bird angled slightly, I was able to see a bright white basal third of the long tail and the smaller head. I shouted Golden, and everyone began cheering and concurring. The excitement was palpable as the bird continued to glide towards us.

I had been hunched over my scope straining to watch this bird. When I stood up to relax for a second, I noticed that half the scopes were pointing north and half east. I shouted there must be two goldens, that half the people were looking at a different bird than I had been. Everyone looked up, and then over, and sure enough, half of us had found one golden eagle and half another. The northerly bird slowly glided over, revealing a lot of white in the flight feathers, a long rectangular white patch in each wing. My golden, following a few minutes later, had a lot less white in the wings. Strangely, after not having had a golden for two months, two occurred at the same time, They were followed by a third golden just a few minutes later, a bird with very little white in the wings or tail. It was a terrific fifteen minutes, but we all had to laugh. If one of us had not looked briefly at the hawk watchers instead of the hawks, would we have ever noticed there were TWO Golden Eagles?

Golden Eagle photograph by Joseph Kennedy. Used with permission. (Not one of the "Lighthouse" birds.)

Wednesday, November 3, 2010

Ramblings on Migration in Tropical America

What images come to mind when you think of migration? Geese flying south in V-formation? Exhausted warblers resting on Gulf Coast beaches? Broad-winged hawks kettling their way south along the Appalachians? I think about the familiar cycle of migrating birds that breed in temperate forests and winter further south.

I must say that spending time in the tropics – most recently on HMANA’s Costa Rica trip – has given me a different perspective on migration. I no longer refer to the local New Hampshire breeders in my area as “our birds”. It’s hard not to when a Baltimore oriole arrives in your backyard in spring, spends the summer there raising its young and keeping you company with its lovely song and bright plumage. We feel connected to this and a sense of this bird and its young “belonging” here. But think about how much time that oriole spends with us versus time spent on migration and in the tropics throughout the winter. A mere three months, maybe four? Baltimore orioles were all over many of Costa Rica’s tropical forested habitats this October, and many of them are settled in until spring! In truth, the oriole (and many other familiar breeding birds of the Northeast US) spends the majority of its time in the tropics and comes north to the temperate forests to take advantage of a very brief food supply and a place with fewer competitors.

The more I learn about migration, the more questions I have. One thing that is certain is that migration is a constantly changing and widely variable phenomenon. Throughout North America, we have short and long distance migrants, complete and partial, altitudinal migrants, and irruptives, to name a few types of migration strategies. But what about those species which carry out their migrations within tropical latitudes? HMANA’s recent trip to Costa Rica to witness migration touched on this spectacle.

On a drizzly afternoon, our group watched four resplendent quetzels feeding in an avocado tree at 2000m on the road to Volcan Irazu. They were taking full advantage of this fruiting tree, but in typical falls, these birds will migrate further south on the Caribbean slope and mainly be found between 500-800m.
From our hotel room in San Jose, my husband and I watched a distant fruiting Jamaican Plum tree through our scope for one hour. Within that time, 20 different species of birds fed at this tree, most of which were migratory species.

Historically, most migration research has focused on movements of birds between temperate and tropical habitats, but the ‘intrartropical’ migrants – those birds moving within the tropics – haven’t received as much attention. According to Gary Stiles, coauthor of Birds of Costa Rica, approximately half of the bird species found in Costa Rica show some evidence of seasonal movement. These movements likely reflect changing food availability and/or weather changes (wet vs dry seasons). There are even a few tropical species that travel long distances to follow burned areas – ‘fire followers’. Food is still the underlying reason for their movement.

It’s easy for us to notice migrating flocks of swallow-tailed and plumbeous kites (large birds moving through the open sky along ridges and coasts), but most other movements happen very quietly, which is part of why this movement was overlooked for so long.

Today, more tropical research has taken place within Costa Rica than any other area in the neotropics, and it is thought that the local migration patterns between mountains and lowlands are probably typical of the rest of Central America. Birds are making localized short distance movements up and down in elevation. If you’re a bird that doesn’t shift its diet when food becomes scarce, then you have no choice but to move. Interestingly, the species most likely to migrate are the fruit and nectar eaters since this food supply changes seasonally more than insects do. Hummingbirds, parrots, toucans, quetzals, and bellbirds are just some bird families that employ this strategy seasonally.

If you are as fascinated as I am about migration in the tropics, or just curious about general behavior and breeding of tropical birds, be sure to check out Birds of Tropical America by Steven Hilty. It’s a terrific book and has answered so many of my questions about migration and more.
(Photo: plumbeous kite at the Kekoldi Hawkwatch)