BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Speotyto cunicularia | Burrowing Owl 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Life history:  Burrowing owls begin nesting in spring in burrows that
they line with cow, horse, or bison (Bison bison) dung [63].  In eastern
Colorado, burrowing owls lay eggs in May [16].  The female does all
incubation and brooding [28].  Clutch size is large, from 6 to 11 eggs
[31], with an average of 6.5 eggs [51].  Eggs are laid at intervals of
24 to 72 hours.  Incubation period is 27 to 30 days and begins when the
first egg is laid, resulting in a multi-aged brood [16].  Owlets are
born partially covered with down and with eyes closed.  Eyes open at 5
days of age [28].  Owlets move among nest burrows when 10 days old [31].
They fly well by 6 weeks of age, and fledge when about 44 days old [43].

At Davis, California, a DNA fingerprinting study of burrowing owl showed
that 37 percent of adult owls were raising owlets other than their
biological offspring.  Owlet movement and polygamy accounted for some of
the discrepancy; intraspecific brood parasitism may also be a factor
[38].

Migration:  Burrowing owls are migratory, but little is known of their
migration routes and wintering areas.  The majority of burrowing owls
that breed in Canada and the northern United States are thought to
migrate south during September and October and north during March and
April.  Burrowing owls migrating to Saskatchewan arrive in early May
[28].  Banding studies suggest that Canadian burrowing owls migrate
further south than burrowing owls in the United States [33].  Christmas
birds counts show California as the most important American state for
wintering burrowing owls, followed by New Mexico, Florida, Arizona, and
Texas, respectively [36].  Florida, the Southwest, and southern
California have year-round burrowing owl residents as well as winter
migrants [28].


PREFERRED HABITAT : 
Burrowing owls occupy grasslands, shrub steppes, and savannas.  They also
occur in other open areas such as agricultural lands, old fields,
extensive forest clearings, airports, golf courses, and spacious
residential zones [1,3,23,50,63,76].

Home range:  In central Saskatchewan, home range size for six
radio-tagged males varied from 0.06 to 1.92 square miles (0.14-4.81 sq
km), with an average of 0.96 square mile (2.41 sq km).  Diurnal
activities were restricted to within 825 feet (250 m) of the burrow
[30].


COVER REQUIREMENTS : 
Burrowing owls typically live in colonies, using burrows excavated by
other animal species for cover [63].  Burrows are used for breeding,
nesting, and brooding [28].  When selecting a burrow, the owls prefer
burrows with low, open cover that provide good horizontal visibility
[23].  Burrowing owls are commonly found in plant communities in early
stages of sucession because cover is low [45].  Long-abondoned burrows
are usually not used because the burrow entrance has become overgrown.
Burrows adjacent to burrows occupied by other burrowing owls are
prefered, although burrowing owl pairs have nested alone if other
burrowing owls were not in the area [28].  Burrowing owls often evict
other animal species from desirable burrows [63].

In the Plains States, burrowing owls use black-tailed prairie dog
(Cynomys ludovicianus) burrows most often [45,56,63], although burrows
of ground squirrels (Spermophilus spp.) are also frequently used [17].
Deserted black-tailed prairie dog towns become unsuitable as burrowing
owl habitat within 1 to 3 years [9,10].  White-tailed prairie dog (C.
leucurus) burrows are used infrequently because plant cover surrounding
white-tailed prairie dog burrows is usually too high for burrowing owl
requirements [48].  In California and Idaho, burrowing owls primarily use
ground squirrel burrows [23].  Florida burrowing owls occupy raccoon
(Procyon lotor), snake (Serpentes), and gopher tortoise (Gopherus
polyphemus) burrows [63].  Other burrows commonly occupied by burrowing
owl throughout North America include those of badger (Taxidea taxus),
pocket gophers (Geomyidae), fox (Vulpes and Urocyon spp.), and
rattlesnakes (Crotalus spp.)  [22,26,63].  Length and depth of the
burrow depends upon the requirements of the species that dug it [28].
In friable soil, burrowing owls dig their own burrows when suitable ones
are not available [23,63].  In Forida, where burrowing rodents are
scarce, Florida burrowing owls dig their own burrows in sandy soils.  The
burrows are about 6.5 to 9 feet long (2-3 m) and less than feet 3.3 feet
(1 m) deep when burrowing owls excavate them [49].

Burrowing owls use ground cavities other than burrows for cover.  On the
Snake River Plain of Idaho, they sometimes use cavities in basalt
outcrops [40,53].  Burrowing owls also use human-constructed cavities
such as culverts.  Pipe can be laid down for artifical nests [11].  In
California, hatching success rate of burrowing owl eggs laid in
artificial nests was 55 percent [43].


FOOD HABITS : 
Burrowing owls hunt in both day and night.  They hunt on the wing, from
prairie dog mounds or other high spots on the ground, and from
fenceposts or other elevated perches.  Prey is either run down on foot
or caught by hovering and swooping [63].  Arthropods, mainly insects,
form the majority of the burrowing owl diet.  An overall assessment of
the burrowing diet in western North America, calculated from 3,564 prey
items, included 90.0 percent invertebrates (mostly insects), 6.9 percent
mammals (mostly rodents), 2.0 percent herptiles, and 0.3 percent birds
[59].  Young prairie dogs (Cynomys spp.), ground squirrels, pocket
gophers, voles (Microtus spp.), mice (Heteromyidae, Muridae, and
Zapodidiae), young cottontails (Sylvilagus spp.), and young jackrabbits
(Lepus spp.) are common mammalian prey.  Grasshoppers (Acrididae),
Jerusalem crickets (Gryllacrididae), and beetles (Coleoptera) are the
most common arthropod prey, although other arthropod taxa are taken as
available [22,24,45,63].  Herptiles are a large component of the Florida
burrowing owl's diet [28].

Seasonal variation:  In Oklahoma, vertebrates comprised 85 percent of
the burrowing owl winter diet, while arthropods comprised almost 100
percent of the summer diet [9].  A study of the spring and summer diets
of burrowing owl on the shortgrass prairie of Colorado showed that most
rodents were taken in April.  Most Jerusalem crickets were taken June,
most grasshoppers in July, and most dung beetles (Scarabaeinae) in
August.  Ground beetles (Carabidae) were taken in quantity throughout
spring and summer [47].


PREDATORS : 
Rattlesnakes and prairie dogs raid burrows for burrowing owl eggs and
nestlings [4,63].  Hawks (Accipiter and Buteo spp.), falcons (Falco
spp.), great horned owl (Bubo virginianus), coyote (Canis latrans),
domestic dog (C. domesticus), badger, skunks (Spilogale, Mephitis, and
Conepatus spp.), weasels (Mustela spp.), and bobcat (Lynx rufus) prey on
both adult and nestling burrowing owls [28].


MANAGEMENT CONSIDERATIONS : 
Factors in population decline:  Intensive agriculture or development
results in loss of burrows, loss of foraging habitat, and creation of
suboptimal nesting habitat.  It also increases vulnerability to
predation [26] and may reduce the chances of unpaired owls to find mates
[28].  Loss of habitat has been cited as factor of decline in the Bay
Area and Central Valley of California [13,23] and elsewhere.  Breeding
Bird Survey data show that in the Great Plains, burrowing owl
populations declined an average of 0.71 percent per year from 1966 to
1987 [54].

Programs to destroy prairie dogs and other burrowing rodents have
greatly reduced burrowing owl populations by reducing the amount of prey
and burrows available [4,23,28,63].  Poisons used to destroy rodents
probably have a direct effect on burrowing owls:  at least one
rodenticide (carbamate) has been shown to lower burrowing owl
reproduction and survival when sprayed over nest burrows [37].  The
effects of consuming poisoned prey on burrowing owl are not well known
[28].  However, weight of breeding burrowing owl in pastures where
strychnine-coated grain was used to control ground squirrels was
significantly lower than on control pastures, suggesting either a
sublethal effect or less available food [36].

Reintroduction:  Burrowing owls were reintroduced in British Columbia in
1986.  As of 1993, 91 fledglings had been produced.  No returns of
burrowing owl reintroduced in Manitoba or Minnesota have been recorded
[28].

Florida burrowing owl:  Human activities have had a beneficial effect on
Florida burrowing owl.  Mowing, cattle grazing [44], and wetland
drainage have increased the subspecies' range.  Residential and
industrial areas currently support the largest populations [49].

Grazing effects:  Moderate grazing can benefit burrowing owl by keeping
vegetation around burrows short [23].  In Florida, cattle often break
through the sandy soils and damage burrows, but overall, cattle grazing
has benefitted the Florida burrowing owl [28].  Overstocking can harm
burrowing owl, however.  Burrowing owl have become extirpated from some
islands of Tierra del Fuego by domestic sheep trampling their burrows
[32].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Speotyto cunicularia | Burrowing Owl