Biology Reference
In-Depth Information
banned for waterfowl hunting in the United States since 1991. But lead shot is still per-
mitted in most areas for hunting upland game birds such as grouse and pheasants, and
hunters are permitted to use lead bullets for deer and other large game.
Scavengers, such as vultures, condors, and eagles, that feed on pheasants and other
upland game birds that have been shot but not retrieved are often poisoned by lead shot.
Those that dine on large chunks of meat or gut piles from deer may ingest fragments of
lead bullets that, like lead shot, remain in the gizzard, dissolving and slowly poisoning
the birds.
The most common cause of mortality for California Condors that have been released
back into the wild has been from lead poisoning. Chemical analyses of the lead in these
birds matches the forms of lead used in the manufacture of bullets, so in 2007, California
passedalawrequiringdeerhunterstousecopperbulletsinspecifiedareaswherecondors
forage.
Many scientists and conservationists believe lead bullets and shot should be banned
for all hunting, arguing that other nonendangered species are also ingesting lead. Their
case is gaining supporters among human health advocates as new research is finding sig-
nificant lead amounts in venison eaten by hunters and donated to food shelves.
Q Why do owls regurgitate pellets?
A
After an owl's prey is dissolved in the glandular stomach, the gizzard squeezes the di-
gestiblematerial intotheintestineswhilethebones,fur,teeth,andotherindigestible mat-
terremain.Whenalltheliquidisfinallysqueezedout,whatremainsisspitoutasapellet.
Hawks, crows, nighthawks, gulls, and some other birds also occasionally or even daily
spit out undigested material as pellets, but owls produce the most solid ones.
The pellets collect beneath branches where owls roost during the day, providing both
a useful clue for birders as to where an owl might be spotted and important information
for researchers who are surveying small mammal populations. Such surveys help to de-
termine how best to deal with agricultural pests that cause major economic problems for
farmers.
Because owls usually swallow small prey whole or in two bites, the bones in an owl
pellet tend to be fully intact and are usually easy to identify. Hawks, however, typically
tear their meat apart, eating fewer bones in the first place, and hawk stomach secretions
are significantly more acidic than those of owls, dissolving many of the bones they eat.
Abird'sskull must house its enormous eyes and a brain large enough to coordinate keen
vision with precise muscle control. Because their food is pulverized in the gizzard, birds
have neither teeth nor a bony jaw to support them.
