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A male burrowing owl busily goes about his
business of the day, collecting dried cow dung in his beak and scurrying
back to his burrow. He deposits it at the entrance, turns around and
trots off to get more. Meanwhile, his mate carries the dung into the
burrow and shreds it with her beak. No other owl so deliberately lines
its nest. By the time this pair of burrowing owls stops its work,
there is a ring of dung around the entrance to their burrow, and the
tunnel and nest cavity are all lined an inch deep. This is clearly
no casual endeavor. But what are the owls doing?
A likely answer comes a few nights later. A badger wakes as usual
at dusk and sets off, hungry, to look for food. He is a powerful forager,
keen-nosed and a fast digger. He takes a little detour up to some
abandoned ground-squirrel burrows. He moves from hole to hole until
he arrives at the burrow occupied by the female owl. She is heavy
with eggs and has begun a two week retreat, generally emerging only
at dawn and dusk to receive food from the male until all the eggs
are laid. Beneath her on the dung are the first two white, nearly
round eggs. She has already begun incubation, so the chicks will hatch
sequentially, rather than simultaneously. She hears the badger approach
and stiffens. The sound of the badger's sniffing seems amplified,
piped down the tunnel of the burrow. He pauses and rechecks the information
that his nose has delivered. The burrowing owl is braced for the sound
of digging to begin. In no time the badger could have his black nose
shoved into the nest chamber, pausing to draw a deep breath of her
scent before he collapses the burrow and devours the eggs — and
perhaps the owl as well. But the badger smells only cow dung. He circles
the hole to get another angle on the smell, and then, satisfied that
the odor of dried dung has nothing to do with food, ambles on. |
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It has been observed that nesting success
is considerably higher in dung-protected burrows. In Oregon, a study
showed that of 25 nests lined with dung, only two were lost to badgers;
while in the same location, 13 out of 24 unlined nests were lost.
If the dung is removed from a burrow, it is usually quickly replaced
by the owls. Interestingly, while cow, horse, and even dog feces are
used, other material has also been found in burrows, including corn
cobs, rags, gum wrappers, shredded newspaper, pieces of bone, animal
remains, and a whole mitten. In one colony near a golf course the
owls diligently went some distance to collect divots for their nests.
Not surprisingly, nesting success was not improved with the addition
of divots.
The burrowing owl is one of only two owls in North America that does
not lay its eggs in an elevated nest. The other is the snowy owl,
which nests on the tundra. But snowy owls are commonly 24-inch birds
with four- to five-foot wingspans. The male is a formidable defender
of his nest, using outright attack and the more indirect "broken
wing" ploy practiced by killdeers. The burrowing owl, on the
other hand, is robin-sized, a mere nine or ten inches long. In this
owl's treeless habitat, it is easy to see how hiding eggs in subterranean
holes could easily evolve into the principal nest-defense strategy.
Traditionally, burrowing owls have been associated with prairie dogs,
which like the owls live in colonies. It is hard to imagine a place
that supplies more suitable nesting holes than a healthy prairie dog
"town." The colony contains 30 to 50 burrow entrances per
acre, each entrance leading to a tunnel that normally runs three to
six feet beneath the surface for a distance of about 15 feet. Observers
once thought the birds and the rodents lived together, but actually
the owls only nest in a burrow vacated by its former owner.
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NEST
Burrow of prairie dog or other mammal, often lined with dung and grass.
HABITAT
Open grassland, prairie, and cleared areas such as golf courses and
airports.
EGGS
7-9, white
INCUBATION
21-28 days, by female
BREEDING RANGE
Appropriate habitat in scattered areas of the western half of the
United States and Mexico; also southern Florida. |
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