Biology Reference
In-Depth Information
route averages 1,864 miles (2,999 km) over water, sometimes requiring a nonstop flight
ofupto88hours.Toaccomplishthisflight,theBlackpollWarblernearlydoublesitsbody
mass beforethetripandtakes advantage ofashiftinprevailing winddirection todirect it
to its destination.
The longest nonstop flight ever recorded for a bird wearing satellite tags was a female
Bar-tailed Godwit, a shorebird that flew 7,145 miles (11,496 km) from Alaska to New
Zealand without taking a break for food or drink during the nine-day journey in October
2007.
NIGHT FLIGHTS
Radar studies have shown
that nocturnal migrants, including most songbirds, fly at
differentaltitudesatvarioustimesduringthenight.Thesebirdsgenerallytakeoffshortly
after sundown and rapidly reach maximum altitude. They remain high until about mid-
night, at which point they gradually descend until daylight. There is considerable vari-
ation, but most small birds appear to migrate at between 500 and 1,000 feet (152-305
m). Some nocturnal migrants (probably shorebirds) fly over the ocean at 15,000 or even
20,000feet(4,572-6,096m).Nocturnalmigrantsalsoflyslightlyhigherthandiurnalmi-
grants.
Flocks and Formations
Q Hawks are supposed to be solitary, but I saw a whole flock of them migrating. Do
they band together for protection?
A
Mosthawksaren'tgregarious.Butduringmigration,manyspecies,particularlythebu-
teos (the group of hawks that are often seen “making lazy circles in the sky,” as in the
song “Oklahoma”), seek out rising columns of air called “thermal air currents” and “up-
drafts.”Whenahawkfeelsoneoftheseaircurrents,itwidensitswingsandtailtoprovide
maximum surface area and begins circling as the air column carries it up in a spiral.
Thehawkclimbs ashighastheairwillcarryit,thenpullsitswingsbackinsomething
ofanarrowshape,andglidesforwardinthedirectionit'smigrating.Nowit'ssteadilylos-
ing altitude, but it may cover quite a distance before reaching treetop height; and mean-
while, on a good day, it's found another thermal or updraft. Gliding between these rising
