Biology Reference
In-Depth Information
Q How do birds prepare for long migrations?
A
As days shorten at summer's end, photoreceptors in their brains trigger hormonal
changesthatstimulatemanybirdstomoltintonewfeathersthatwillstanduptotherigors
of a long flight. Their hormones also trigger a huge appetite, and they start eating vora-
ciously, gaining significant amounts of weight. Many insectivorous species supplement
theirdietwithfruits,grains,andotheritemsthatcanbeconvertedtobodyfat,whichbirds
burn efficiently for energy. These hormonal shifts make birds increasingly restless, espe-
cially at nighttime. Suddenly, one day it's time to go!
Many of the best places for witnessing migration are along coastlines and bluffs. Watch
for hawks and other birds that ride on thermal air currents. Warblers, thrushes, and other
songbirdsthatcoverlongdistancesbynightaremorelikelytobedowninthevegetation
feeding and resting. You can often find them by listening for chickadees, because when
warblers and vireos are passing through an unfamiliar area anywhere in North America,
chickadeesallowthemtojointheirfeedingflocks.Chickadeesknowwherethebestfood
is and where predators are mostly likely to be lurking.
Q I've noticed that the male Indigo Buntings in our area look so bright and shiny in
the spring, but by the end of the summer, they are drab and dull. What happens to
them?
A
Late every summer, after breeding, male Indigo Buntings molt out of their bright blue
feathers into drab brown ones. They keep these feathers through their migration to the
tropics and during most of the winter, and then in late February or early March they molt
into their bright blue feathers once again just before returning north.
