Biology Reference
In-Depth Information
Bird feathers are wonderful for protecting their bodies from extreme temperatures,
rain, wind, and too much ultraviolet light, but over time feathers grow frayed and parts
break off. Molting provides a great way of replacing them before their general wear and
tear cause problems. In the case of Indigo Buntings, the bright blue plumage of males is
very useful when they're trying to attract mates and defend their territories but is not so
helpful in winter, so the feathers they grow at that time make them less conspicuous.
By the way, the blue in their feathers is due to the way the outer layers of cells in the
feathers reflect light, not due to any pigments. If you were to grind up a few male Indigo
Buntingfeathers,youwouldn'tseeatraceofblue—thefeathersarepigmentedtobedull
grayish brown. The blue color is most intense when sunlight is bouncing off it, and least
intense when the bird is backlit or in low light.
HITCHING A RIDE
I've often been asked if hummingbirds hitch rides
on the backs of geese while mi-
grating — a rather charming concept but definitely a myth. So where did this idea come
from? Once I saw a Ruby-throated Hummingbird that was perched on a wire become
suddenly agitated. I looked up in the direction it was looking to see a Bald Eagle flying
high above. The eagle had apparently crossed into the hummingbird's column of defen-
ded airspace, and the hummer took off straight for it.
When it reached the eagle, the hummer started dive-bombing it on the upper back
and nape, up, down, up, down, like a little avian yo-yo. Eventually, the eagle must have
crossed out of the hummer's defended airspace. At that point, the little guy flew back
down to his wire, chirping animatedly like he'd chased the big bruiser away.
Hummingbirds will attack virtually any large creature that enters its feeding territory.
I wonder if someone once saw a hummingbird dropping down or flying toward a goose
and thought it was hitching a ride, rather than maneuvering for an attack. I did read of
oneaccountbyahunterwhoshotagoosethathadadeadhummingbirdtangledinweeds
on its back. If true, that's hard to explain, but it may be because the hummer got tangled
while doing a dive-bomb. I think people just find it hard to believe that tiny humming-
birds can migrate so far — it may just seem more believable that they hitch a ride!
In fact, though, hummers can even fly across the 600-mile (965 km) Gulf of Mexico
on their own. We know this because specially licensed bird banders capture, weigh, and
band hummingbirds in southern Texas, Louisiana, and Mississippi before they cross the
Gulf. Other researchers capture the hummingbirds when they arrive on the Yucatán Pen-
insula and weigh them again. The average difference in weights fully accounts for the
birds flying nonstop over the Gulf of Mexico on their own power.
