Biology Reference
In-Depth Information
ing,notforcarrying prey.They swallow the fish,flytothe nest, andregurgitate it totheir
young.
THE TASTE TEST
Birds that are specialized may be limited in food choices by their own bodies. But
even generalists are limited in their food choices. Blue Jays are omnivorous, and during
the course of their lifetime travels, they encounter many unfamiliar food items. Some
berries and insects that seem perfectly fine may actually be toxic.
To test whether a novel item is edible or not, the Blue Jays I've observed in captivity
take a fairly small taste and wait several minutes before eating more. If the item proves
to be noxious, the jay will avoid similar items in the future; if not, the jay won't delay in
feeding on it the next time it's offered. In one famous case, a captive jay ate a monarch
butterfly that quickly made him vomit. After that, the jay always avoided orange butter-
flies even though other orange species aren't toxic.
Great Gray Owls normally feed on small mammels, especially meadow voles, which
theycanhearwhenthevolesaredeepintheirtunnels,evenwhenthosetunnelsareburied
under 18 inches (46 cm) of snow. The owls' big ears, large but not very strong talons,
and huge wings, which can push this fairly lightweight owl out of deep snow, are adapt-
ations for catching their small, hidden prey. When vole populations crash, the owls may
“invade” new areas en masse. Some will continue to feed almost exclusively on voles,
but a few will learn to take other species. During the winter of 2004-05, hundreds of
Great Gray Owls descended on northern Minnesota; some individuals were documented
feeding on rabbits, squirrels, and even muskrats, but the majority stayed in grassy areas
searching for voles.
Q How can Bald Eagles survive in northern areas after all the lakes have frozen?
A As much as eagles enjoy fresh fish, they will also dine on carrion and garbage. It may
be disconcerting to see the emblem of the United States of America eating at a dump, but
the ability of eagles to exploit a wide range of food choices is what makes them so suc-
cessful.
Crows steal food from other animals. They have been observed distracting a river otter
tostealitsfishandfollowingCommonMerganserstocatchtheminnowstheduckswere
chasing into shallow water. They sometimes follow small songbirds as they arrive from
a long migration flight and capture and eat the exhausted birds. They may follow song-
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