Geography Reference
In-Depth Information
million tons of seed enters the avian food chain through bird feeders. That is
roughly the same as the amount of corn, wheat, and rice that the U.S. gov-
ernment donates annually to feed people in Africa. At an annual cost of $3.5
billion, this of ering fuels human as well as avian economies. It is no wonder
that 350 species of birds have been reported eating at feeders in the United
States.
Feeders enable migrating species to live farther north and at the same
time lengthen the breeding season and enhance overwinter survival for many
resident species. Cardinals, tufted titmice, and Anna's hummingbirds are
marching north because of feeders. Suburban Florida scrub-jays, an endan-
gered species, use protein-rich peanuts to breed earlier than their wildland
counterparts. Local abundance of granivorous birds—those specializing on
seeds, such as chickadees, tits, i nches, house sparrows, and blackbirds—
increases in proximity to feeders, but this does not appear to translate into
abnormally high breeding densities. Black-capped chickadees, for instance,
crowd onto feeders and survive better over the winter by doing so. Yet come
spring, the deeeee- deeeee song of males apportions the breeding population to
well-defended and typically sized territories. Those birds that survive the
winter but fail to obtain a breeding territory likely i lter into less optimal hab-
itats where they queue for better territories and provide an important reserve
should breeder numbers in prime real estate crash.
The calories in supplemental foods, especially those from fat and protein,
allow birds to emerge from winter in better condition than birds reliant on the
natural foods available during a northern winter. The condition of a bird in
the spring may directly enhance reproductive output. In Flagstaf , Arizona,
pinyon jays l ock to feeders for oily sunl ower seeds and peanuts. This behav-
ior often enables the “town l ock” to lay an extra egg relative to l ocks that re-
lied only on the boom-and-bust production of native pine seeds. In Ireland,
researchers tested this idea by hanging peanut feeders in forty-i ve forests and
monitoring the reproduction of resident blue tits. After six weeks and about
 
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