BACKGROUND:
Owl pellets are used for scientific study of small mammals
and their distribution. Owls hunt at night and roost during
the day. They are ravenous feeders, eating almost anything that walks,
crawls, flies or swims. When an owl roosts, it then will regurgitate
what it ate the previous night. Charting the contents of the owl
pellet can then help wild life biologists to determine the population and
age of what the owls ate.
Owls have no crops like most birds, so indigestible parts (hair,
feathers, bones) are passed forward into the proventriculus until regurgitated
as pellets. Owls are predators who feed mainly on rodents. A barn
owl can eat one and a half times its own body weight in rodents in one
evening, reflecting the population of rodents in the area. An owl's
talons and beaks are adapted for its diet. An owl kills with its talons
rather than its hooked beak. The great horned owl, one of the few
enemies of the skunk, approaches a skunk from behind and punches its curved
talons through the skull bones and into the brain, killing the skunk instantly.
Wildlife managers are interested in population biology, or the
study of the growth and structure of populations together with the factors
that regulate their size and cause fluctuations in their density. In fact,
this could be called demography which looks at the population dynamics
of any organism including humans. The demography of organisms is
always changing. For example, a drought is persistent for a few years
in an area. One of the first things affected is usually the birth
rate. If the rate of birth goes down, the population may suffer and
in some cases be totally eradicated.
PROCEDURE:
Have the students complete the worksheet. It is
actually an accumulated amount of data. For each set of owl pellets
the information will be different. If you have purchased the module from
the Math/Science Nucleus your pellets will reflect a collection period
of over 15 days for a Great Horned owl in Fremont, California (San Francisco
Bay area).
- Each student group should describe what they found in
their owl pellet. They should justify their number of organisms, as well
as the type of organisms.
- Discuss with students what they think the rodent population
is composed of in the area.
- See if there was any problems. For instance, on
day 4 and 5 the only things found in the owl pellets were some kind of
crayfish. What could that mean? It may have been raining,
and the rodents stayed in their nest.
