Mystery lurks in the night sky

**Mergie Master** · 09-25-2010, 01:49 PM

A merlin perches on a dead pine tree on Nantucket Tuesday.
A wave of merlins and other falcons have been migrating south
over the Cape and Islands in recent days.

September 25, 2010

This first birding column of fall 2010 is predictably full of the magic and mystery of migration. After unsettled weather and east winds generally bad for migration on several days last week, the weather broke. When you read this, the Cape and Islands may be swarming with birds that arrived the night before.

These birds had been feeding and resting in the north woods for weeks, biding their time, waiting for the right high-pressure system and northwest winds. All their highly evolved migration triggers, honed through countless generations, told them to head south. They needed to "get out of Dodge" as fast as possible.

The temperatures were dropping, the days getting shorter, and their food supply was starting to dwindle. Yet they had to wait for the right weather to depart.

The clearing frontal system with accompanying northwest winds was what they had been waiting for. Last night, there was expected to be a mass movement of birds heading south.

Nocturnal flight calls

For this writer, there is nothing comparable to looking up at the stars and listening to nocturnal migrants as they stream overhead, uttering subtle but distinct chip or contact notes. It produces a feeling akin to no other. The phenomenon of bird migration is completely remarkable. Sadly, the nights in the fall when one can hear nocturnal migrants in large numbers have been declining for decades, making it all the more poignant when it does occur.

In that lovely September night, thousands, at a minimum — and probably hundreds of thousands, possibly millions — of small insectivorous birds of a staggering variety are engaging in a spectacular migration: thrushes, vireos, wood warblers, orioles, and more. Imagine weighing far less than an ounce and being able to summer in Canada and winter in the Neotropics! Bird brains are far more complex and evolved than any terrestrial being can fathom.

The sheer physical feat of flying extraordinary distances, both in spring and fall, outshines any physical accomplishment achieved by wingless creatures. Compare what any warbler does in a year of its life, or look at the seemingly impossible long-distance migration of a Hudsonian godwit, traveling yearly from the Canadian Arctic to Tierra del Fuego in southern South America, and even a superb human athlete such as Lance Armstrong pales fractionally in comparison.

Standing out on a lawn, ears skyward, listening to the steady but distant sounds in the night sky, one cannot fail to be awed by this fantastic event going on right over one's head. Some sounds we recognize, such as the spring peeperlike nocturnal flight call of Swainson's thrushes, the distinctive peep-peep-peep of a solitary sandpiper, the various similar chips of many warbler species, including blackpoll, bay-breasted, magnolia, black-throated green, parula, American redstart and yellow, to name a few.

But the distinctive calls that are fairly easy to recognize once one is familiar with them are not the majority of what is emanating from the night sky. Most of the calls are still unknown and yet to be deciphered. Birds that migrate at night — most of the small land birds in this part of the world — give different calls while flying in the dark than they do in the day. This is most inconvenient for birders attempting to figure out what is going on in the night sky.

Great strides have been made in the past decade with sound-activated directional microphones and high-tech recording devices. A gentleman named Bill Evans has been working on this, and much of what we are sure of has come from his dedicated and tireless efforts. Yet all we think we know is just the tip of the iceberg. For every call we are able to identify there are 20 more we cannot.

Common or rare

It seems a caveat for birders old and new: Any bird is always a common bird until you can prove that it is not.

Common birds are just that — and beginning birders should regard a species as the expected one until they can prove otherwise with a photograph or by consulting with an experienced observer. It is amazing how often a rare bird will be reported in the newspaper and suddenly reports start rolling in that are just not possible.

After the discovery and reporting of America's first red-footed falcon in August 2004, multiple people claimed to have seen this bird elsewhere, or another of its kind. One is forced to be skeptical about such reports.

The annual spectacular phenomenon of migrating falcons on the Cape and Islands is hitting its peak. These fastest-flying of raptors depend on speed, ripping though the air, in pursuit of other fast-flying birds, and they move south to coincide with most of the land bird migration.

It is hard to spend much time in the field and not see a merlin or a peregrine falcon for the next several weeks. These birds can be seen zipping around wherever one happens to be, even rocketing down the main streets of towns as they make their way south.

Until next week — keep your eyes to the sky!

E. Vernon Laux's birding column appears every Saturday in the Cape Cod Times. Laux is the resident naturalist for the Linda Loring Nature Foundation on Nantucket. You can also hear him on "The Point" with Mindy Todd at 9:30 a.m. the first Monday of the month on the Cape's NPR station, WCAI, 90.1.