Natural History of Burrowing Owls
At one time, burrowing owls were fairly common and widespread over
western North America. However, populations of owls have declined, or
in some cases disappeared altogether, due to the large scale changes
that humans have made to the owls habitat. They are endangered
in Canada and are listed as endangered or threatened in a number of
states. Burrowing owls are now a federally listed Species of Management
Concern and are a Species of Special Concern in California.
Where are they found?
Burrowing owls are found from Canada to South America. They inhabit
most western states in the United States and have a disjunct population
in Florida. In California, burrowing owls are found mostly in grasslands.
Burrowing owls are either year-round residents or migratory, depending
on where they live. Little is known about where the birds actually migrate
to, but California appears to be the most important state for burrowing
owls during the wintertime. The owls nesting in California are primarily
year-round residents. Burrowing owls are generally found in low-lying
grassland areas and semi-desert. They require open habitats that contain
suitable nesting burrows, usually with short grasses and sparse shrubs.
They avoid thick, tall vegetation, brush, and trees, perhaps because
these areas provide places for predators to hide. Native grassland habitat
is disappearing because of agricultural, industrial, and residential
development and invasion by non-native plant species. Burrowing owls
are being forced to rely on less natural habitat for survival.
When do they reproduce?
Reproduction begins the year after hatching. The nesting season (courtship
and egg-laying) occurs between February 1 and August 30, depending on
location. Females lay up to 12 eggs and incubate them for almost four
weeks. Males bring food to the females during the incubation period.
He also brings food for the chicks and mother during the early nestling
stages. The young are capable of short flights by week 4, and fly well
at week 6. They are still fed by their parents for another 6-8 weeks,
and remain near their nest burrow until fall. If you visit in July,
you are likely to see the chicks and adults nearby their nest. By this
time, most chicks are as large as their parents.
How long do they live?
The lifespan of wild burrowing owls is essentially unknown. The record
currently is held by one banded owl that survived 8 years, 8 months.
Much of our research involves understanding factors affecting the owls
survival and reproduction.
What do they eat?
Burrowing owls are opportunistic feeders; that is, they eat a wide
variety of things as they become available. Although you may often see
burrowing owls during the day, most of their time searching for prey
is during the night. Prey items include mammals, birds, reptiles, amphibians,
insects, spiders, centipedes, scorpions, crayfish, and molluscs. The
majority of the diet is made up of small mammals (pocket gophers and
voles) and insects (grasshoppers, crickets, and beetles). One way to
learn about what owls eat is to examine pellets. Pellets are comprised
of prey remains that the owl cannot digest. These remains, bones for
example, are regurgitated in the form of pellets.
Where do they nest?
Like the name suggests, these owls nest in burrows. They use vacated
burrows made by mammals such as ground squirrels or similar holes in
the ground. The owls activity is tightly centered around the nest burrow
during the breeding season. They may use more than one burrow within
their territory during the breeding season. This may be an anti-predation
strategy; if one burrow is found by a predator, some of the young might
survive in another burrow. Nest burrows are very distinctive because
the owls line the entrance with material such as cow manure, insect
parts, cotton, dead toads, plastic and tin foil. If you find a nest
burrow, it is important not to disturb it. Try moving away and waiting
for the owls to emerge or return. They are fun to watch!