Biology Reference
In-Depth Information
ent whistles with as good an imitation as I could muster. Soon I saw him at the top of a
tree, looking right at me when I whistled. I have no idea what prompted me on a frozen
February day, but I took off my glove and raised my hand, and he lighted right on my
finger! He looked at me and whistled, I whistled back, and he gave me one last whistle
before flitting back into the trees.
It was one of the most thrilling moments of my life. But it may well have been one
of the most disappointing for the grosbeak. I think my whistling back to him must have
given him hope that he'd found another grosbeak flock, but all he found was a clumsy,
flightless human.
Q Why are Saw-whet Owls so small?
A
Birdsizeisdeterminedbyacombinationofthings.OneofourlargestowlsistheGreat
Gray Owl, which specializes on pretty much the same size food that Northern Saw-whet
Owls eat — very small rodents. The Great Gray Owl takes advantage of its huge ears to
hear meadow voles when they are buried under deep snow or meadow grass; it flies in
and plunges to grab the vole, then uses its huge wings to pull back out. The problem with
having such a large body is that it must catch a lot of mice to survive.
Northern Saw-whet Owls are too tiny to hunt where snow or grass is so deep, but they
live in forests where snow isn't as deep, especially around tree trunks, so although they
don't eat as many mice as Great Gray Owls do, they can find enough to keep their tiny
bodies alive.
Their size makes them very maneuverable in flight, and they can also obtain a good
amount of the nutrition they require from large insects in summer. In addition, Northern
Saw-whet Owls are small enough to take shelter in woodpecker holes, which Great Gray
Owls certainly can't do!
Bird feathers insulate the bird, protecting it from too much heat and cold, but they can
also hold an incubating bird's heat away from its eggs. So at the time eggs are laid, belly
feathersonmostfemalebirds,andthemalesinsomespecies,becomeloose.Theparents
pluck them out, often to use as part of their nest lining, so they can press their warm ab-
dominal skin directly on the eggs to heat them.
