Thursday, September 13, 2012

9/11 - A view into bird migration

On the solemn day of 9/11, the Tribute of Light lit up the New York sky in memoriam. As we all remembered that faithful day in 2001, one man, Cornell Ornitholigist Andrew Farnsworth, planned for a night of birdwatching...in art from the roof of the Empire State Building. Farnsworth saw a great ornithological opportunity in these lights of remembrance: this time of the year, the Northeast experiences enormous bird migration almost every night, and from atop the skyscraper, Farnsworth could count each bird that flew through the columns of light, and, in so doing, get an accurate picture of which birds were migrating over.

The Tribute of Light. Photocredit Greg Chow
Farnsworth has a special interest in night-migrating birds. He is an associate in one of the Cornell Lab of Ornithology's ground-braking projects: BirdCast. BirdCast is a service that brings live migration forecasts based on knowledge of how migration is affected by weather, and also by eBird reports, radar analysis, and Farnsworth's specialty, acoustic data. The clear night of the 11th along with the revealing lights of the Tribute provided the perfect opportunity to take in data and build on our knowledge.

And reveal they did! From early in the eventing to 10pm, Farnsworth birded from atop the Empire state building, and from 10 on until past midnight, he birded directly from the Tribute lights. It is reported that he saw more than 2, 000 birds and heard the faint flight calls of many more. From warblers to thrushes to grosbeaks and tanagers, Farsworth got them all. The massive bird movement even brought in some herons, rails, and a Peregrine that picked off some disoriented songbirds from within the lights--as the expression goes, like taking candy from a baby. See his full list here.

Here I've attached a recording of one of the most distinctive flight calls, one that you can listen for from your own backyards at night: the Swainson's Thrush. Listen for the roundly sounded spring peeper-like call during the day to--these birds are all over the place if you listen.

There are two things that are revealed by this story. The first is obviously the sheer enormity of the bird movement at night, when we aren't even aware of it. But slowly, the science of birds is putting together the pieces. In the 50's (I think) radar operators began seeing things like this:
Around this time, somebody realized that all that blue is BIRDS (for more about birds and radar, see my earlier post about it or visit woodcreeper.com). As time went on, acoustic data from night flight calls were added to the pool of knowledge, but we're still learning. Night migration is still shrouded in mystery. It's stories like this that show how even in the biggest city in the country, windows into this greatest of natural phenomena are there, and all we have to do...is...well...get on top of the Empire State Building and shoot giant beams of light into the sky. Okay, maybe not all that practical, but what matters is being aware of the processes at play around you, and all that we can learn from them.

The second thing is just that sort of learning. Have you wondered why it was so easy to pick out tiny birds in the giant light beams? Birds just darting through wouldn't give much a chance for identification. The problem is, migrating birds use stars for orienteering purposes, and lights from buildings--or in this case memorials--can be highly disorienting. Many of the birds became disoriented and circled around and within the light, and hovered in place in confusion. This is why that peregrine (see list) had such an easy meal. This is why cities with tall, well-lit skyscrapers can be deathtraps for birds. There's even a hotline in Chicago (and most cities) for dead and stunned birds from collisions with buildings. So what's the solution? Turn off the lights! And luckily, just that was done with the light beams after 12:30 am or so the night after 9/11/12, allowing many of the birds to reorient and continue their migration.

As time goes on, events like these increase our understanding of bird migration, and the more we know, the more we can do to protect it, one of the most important and powerful processes in nature.

Click here to see the first post about this event on the Cornell Lab blog.

Saturday, September 8, 2012

Midair Feeding Strata?

One of the great things about birding in the forest is how easy it is to pick out each bird's ecological niche. For example, on the bottom, you have Ovenbirds and Thrushes, in the middle you have all sorts of warblers, tanagers, flycatchers, tree-clinging birds, etc., and on top you have vireos and certain other flycatchers. And this is just Eastern Woodland birds. All forests have developed these "feeding strata", or levels wherein different kinds of organisms feed on the different food items that are found there. These strata are unique for every forest, and they show how forests evolve and develop relationships as a system, and when one cog in the master machine falls out, the machine can no longer function as a whole.

Another classic example of feeding strata is underwater, in coral reefs or elsewhere. Different fishes feed at different levels. But what about in midair? We all know and love swallows, swifts, and other aerialists whose energy and agility are an infinite source of free entertainment. Do they have different preferred levels at which they feed too? Most of the time, we see these so-called aerialists separately, some swallows at a pond, some swifts of a neighborhood, some nighthawks over a parking lot, etc. But when they come together, it becomes obvious that there are in fact feeding strat in the sky. One morning, not to long ago, a cloud of swallows--multiple species--had gathered over a local marsh. The swallows remained relatively close to the marsh without going more than say 50 feet above the cattails. Below them, in some taller shrubs and small trees, a flock of Cedar Waxwings was displaying their aerial abilities--something they're often not given credit for--by sallying out and then back to catch flying insects, but never in the level of the swallows. Up above the 50 feet of hirundinid madness, Chimney Swifts had gathered to feed on insects higher than the swallows would push for. So clearly some aerial strata have developed: waxwings on the bottom, swallows in the middle, and swifts on top. And what does this tell us? It tells us that each group of birds is adapted to hunting in different altitudes (their niches are different), and in doing this, they avoid direct competition between species.

 This just comes to show that even the littlest, seemingly insignificant observation can tell us a lot about nature, so get out there, keep your eyes and ears open, and who knows what discoveries you'll make!

To top this post off, here's an amazing video of Tree Swallows gathering for migration: