Sunday, May 12, 2013

The Mysteries of Migration

Over the last few years, we have cultivated a relationship with the NYC Audubon, resulting in biweekly Birding Tours of the park during migration. We've been delighted as our Audubon Guide Gabriel Willow teaches us about the avian life of NYC, and helps us spot some of these magnificent creatures up close. Now Gabriel shares his experiences in the park.

By Gabriel Willow

Birders (or bird-watchers, depending on your preference) are perhaps more in tune with the natural world than most folks.  They are, at least, exquisitely attuned to the presence, behaviors, and movements of bird species (if occasionally seemingly oblivious of other things).

This spring, the same question has been on every NYC bird-watcher’s mind and the topic of most of their conversations: where are the birds?  Until the last couple of days, there have been almost no spring migrants.  No tanagers.  No orioles.  Few thrushes, vireos, or warblers.  I have heard terms like “eerie”, “disturbing”, and “creepy” to describe the season’s lack of migratory movement.  It has been one of the most quiet Springs in living memory, and it just doesn’t seem the same to have a sunny April afternoon, the smell of cherry blossoms in the air, but no Black-and-White Warblers or Northern Parulas singing.  Some people have even been worried about mass die-offs or species declines.

From a personal standpoint, it has made my job as a nature educator and bird-watching tour guide challenging.  I lead twice-weekly walks in Bryant Park for NYC Audubon and the Bryant Park Corporation, as well as many other tours and classes around the city.  There’s only so many tours where I can lead a group around silent woodlands and parks, craning our necks futilely in an attempt to glimpse some sign of movement, listening for a call or song.  Is this the silent spring that Rachel Carson had warned us about?  Week after week, I have awkwardly shrugged at the end of a walk, saying “well, I’m sure next week the birds will arrive”.

Happily, it seems that the lack of birds is temporary and weather-related.

We now have technology to track bird movements, and get a better sense of their migratory patterns and whereabouts.

Before I describe these developments, some quick background on migration: why do birds migrate anyway?  Many people think it’s due to cold weather in the north, and that birds migrate to avoid the cold and seek balmier climes in the tropics.  This is true to a degree, but misses the underlying reason for migratory behavior.  It’s not really about the cold’s affect on birds.  They are incredibly cold-hardy animals; feathers are the best insulation in the natural world.  That’s why birds are the only land-animals in Antarctica, the coldest place on earth.  Not just penguins either: skuas, terns, sheathbills, fulmars, and other species all thrive in this incredibly harsh setting.  Many birds do just fine here in the winter as well, as long as they eat seeds, berries, or meat.  It’s all about food!

Those birds that migrate aren’t avoiding the cold, they’re seeking food.  This applies especially to insect- and nectar-eaters, as well as many birds that feed in and around fresh water, which freezes over in temperate winters.

When spring comes, they stream northward by the millions, to take advantage of the great abundance of insects, flowers, and nesting sites to be found among new the growth the season brings.  They come from South America, Central America, Mexico, the Caribbean, and the southern US.  It is one of the great spectacles of the natural world, and those of us who live in NYC are lucky to be located right along the Atlantic Flyway, where migrating birds hug the coastline as they wing their way northward, and seek shelter and food in city parks, the few patches of suitable habitat to be found in this megalopolis.

So what happened this spring?  Why were the birds nowhere to be seen?  Why were the parks silent?

They were basically stuck in traffic, stalled behind a high-pressure system and steady winds from the north-west.  They prefer to migrate with a strong tail-wind, which is usually what happens in the spring, as low-pressure systems and warm southern breezes move into the region.  This spring was unusually cool, and the steady headwind dissuaded the birds from pushing northward.

This week things finally changed, much to the relief and joy of birdwatchers across the East.  Many birds had been migrating up the central flyway, along the Mississippi river, and some were beginning to wonder if they would fan out from the midwest across the north, bypassing our region entirely.  Would it be the Spring Without Migrants?

Thursday finally brought a low-pressure system and warm winds from the south, which also brought heavy rainstorms as this front collided with those stubborn north winds. With the southern winds came birds, physical embodiments of the warmth and color of the tropics.  Finally!  Warblers hopped in the treetops.  Baltimore Orioles whistled their cheerful song.  Flashes of astonishing brilliance revealed Scarlet Tanagers in the foliage.  Bright birds of myriad species seemed to be in every tree and shrub.  Friday May 10th was one of the best days for birding in recent memory.  It seems as though all of the birds were bottled up, waiting for the right wind to carry them, and then they flew forth en mass and all showed up at once.

And this, more or less, is exactly what happened.  We can now actually track the movement of flocks of migratory birds using the same radar that is used to follow weather patterns.  The birds show up on the radar as blue and green cloud-like formations as they fly thousands of feet above the ground, ten or fifteen miles per hour faster than the prevailing winds.  It’s just another way that bird-watching can intersect with science, providing a fascinating glimpse into the interaction of weather and bird behavior.  It’s also a sobering reminder of how climate change and instability may affect birds in ways that are hard to predict.

But for now, we’re just glad to have them back, brightening our parks with their colors and our days with their song.  And they must be glad to have the wind at their backs.

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