Historical facts
Historically, Burrowing Owls in British Columbia bred mainly in the
Okanagan-Similkameen and south Thompson basins: Osoyoos, Oliver, Penticton,
White Lake, Coldstream, Okanagan Landing, Knutsford, Savona, Kamloops,
Douglas Lake and Lulu Island in the Fraser Delta; with occasional records
over a slightly wider area in southern British Columbia - east to the
Kootenay River valley, north to Horsefly in the interior and north to
Comox on the coast.
The last breeding record for Burrowing Owls in BC was in 1970. The species
was designated as threatened in 1979, reconfirmed as such in 1991,
and was re-examined and “uplisted” to endangered in
1995. Except for some recent nests derived from introduced owls,
the species’ breeding population is unknown but there may
still be a few isolated nesting pairs in the Okanagan Valley each
year. The reintroduction of Burrowing Owls has failed to establish
a stable population in British Columbia.
Distinguishing features
Burrowing Owls are unusual in many respects. They are grassland rather
than forest dwellers, they live in underground burrows, are often
active in broad daylight, and eat insects as well as rodents. Ranked
second to the Barn Owl as the most economically beneficial owl in
North America, the Burrowing Owl eats many insects and rodents in
agricultural areas.
Another distinguishing feature of the Burrowing Owl is its tolerance
of non-threatening human activity. Nests are sometimes found in
cow pastures near farm buildings, on airports, or on road right-of-ways.
This tolerance, together with its habit of loafing around the nest
burrow or on fenceposts in daylight, make this one of the most observable
of all owl species.
The Burrowing Owl has been described as a short fat owl on stilts.
The long, bare legs and stubby tail of this plump-looking little
owl are indeed distinctive. It is similar in size to the American
Robin, with a total length (head to tail) of about 24 cm. Long legs
help this "ground owl" see over the low "short-grass"
prairie vegetation in a landscape with few elevated perches, and
also aid in running down insect prey.
Female Burrowing Owls are slightly smaller than males, an uncommon
situation for birds of prey. This may be an adaptation for squeezing
into narrow burrows. The sexes have similar colouration, although
males often appear faded, possibly from spending more time exposed
to the sun. Adults are a rich sandy-brown colour, thickly spotted
with white and buff; the underparts are whitish, barred with brown.
This colouring provides good camouflage in dry grassland habitats.
Other features include a rounded head without ear tufts, yellow eyes,
white eyebrows, and a white throat with a dark brown half-collar. Juveniles
have buffy underparts without bars during the first few weeks after emergence
from the burrow.
Distribution
Map
Red dots indicate specimen records or confirmed breeding sites.
British Columbia
Burrowing Owls historically were found in the Okanagan-Thompson
regions. Since 1928, only three nest sites have been located: one
at Chopaka in the lower Similkameen Valley (1943), another at Okanagan
Landing (until 1963), and a third on the West Bench near Penticton
(1970). Recent nests are found only at the reintroduction sites
near Osoyoos/Haynes Lease and Kamloops.
North America
Breeds across the grassland regions of southern Alberta, Saskatchewan
and Manitoba where there are an estimated 1000-2000 breeding pairs.
In the United States, Burrowing Owls have a
wide distribution in open, well-drained grasslands, steppes,
deserts, prairies, and agricultural lands. They occur in all states
west of the Mississippi Valley, through the western and mid-western
States, and are resident in Florida. They extend south into Mexico,
Central America and South America but populations have declined
in many areas due to habitat degradation.
Habitat
Burrowing Owls require prairie-like terrain with low herbaceous
vegetation, deep soil for burrows,
the co-occurrence of mammals that excavate burrows, and a food supply.
They are adapted to open, dry country with short vegetation. They
are well-adapted to grazed rangelands, but find croplands less suitable.
The terrain they inhabit often is flat, but more rugged landscapes
are also used. The extent of suitable short-grass range-land habitat
is quite restricted in British Columbia.
Over much of the Burrowing Owl's range, it is most abundant in
active ground squirrels or prairie dogs colonies, where numerous
nesting and satellite burrows are available. The availability of
burrows is a major factor controlling the abundance of Burrowing
Owls; burrows dug by badgers also are important in many areas. In
British Columbia there are few burrowing mammals in habitats that
otherwise are suitable for this owl.
A viewing site, marked with a sign, has been set up north of Osoyoos
Lake on Black Sage Road, where the birds can be viewed from a distance
without disturbance.
Why is it endangered?
The overall abundance of Burrowing Owls is limited by the availability
of suitable habitat. The grasslands in which they live are restricted
to the dry valley bottoms of the southern interior, and comprise
less than one percent of the area of the province. This small area
of natural grassland is being overwhelmed by expanding towns, intensive
agriculture, and a multitude of other industrial uses and developments,
especially in the Okanagan Valley. The quantity and quality of grassland
has declined substantially across the Canadian Prairies especially
between 1976 and 1986 as native prairie was converted to crop and
rangeland.
Burrowing Owls historically used badger holes as burrows, and
when cattle were introduced to Canadian grasslands, ranchers shot
badgers to minimize risk that cattle would trip and break legs.
Badgers declined as a result of over-hunting, habitat loss and habitat
fragmentation; without an adequate supply of burrows, the nesting
success of Burrowing Owls was severely impacted.
Control of problem wildlife or other mortality
factors affecting burrowing mammals (badgers and ground squirrels),
limits the burrows available for owls. As well, susceptibility to
pesticides (notably Carbofurans), accumulated in prey items can
affect adult mortality
and reduce reproductive success. Heavy grazing pressure in range
land also may disturb burrows and degrade nearby foraging areas.
Humans have contributed to Burrowing Owl mortality in other
ways in many parts of their range. Some owls, particularly naive
juveniles, feed on road-kills or on insects attracted by warm pavement
at night, and are killed by highway traffic. Others get caught in
fences, hit overhead wires, or are killed by dogs or cats. Some
are shot by vandals.
Burrowing Owls also contend with many natural hazards, such as
predators and adverse weather conditions. However, populations probably
were stable before Europeans colonized the west.
Wildlife managers have attempted to reintroduce Burrowing Owls
to British Columbia. Captive bred birds have been released, starting
in the early 1980s, when about 500 individuals were transplanted
as family units from Washington. Juvenile and a few adult owls were
transplanted near Vaseux and Osoyoos lakes between 1983 to 1990.
They were placed in artificial burrows made from plastic pipe with
an inverted bucket at the end for a nest chamber. Satellite burrows
also were constructed to provide cover for adult males and to give
the developing young space to spread out.
Initial success with the South Okanagan recovery program has been
encouraging. Between 1986 to 1992, 87 introduced owls have returned
as adults and have produced a total of about 90 fledged young. Similar
but smaller introduction programs have also been carried out at
Cache Creek and Douglas Lake, using juvenile owls hatched in captivity.
As of 1995, 5-10 breeding pairs existed in the province because
of reintroduction programs. The long-term goal is to establish self-sustaining
populations of at least ten breeding pairs of owls in each of five
different locations in the southern interior.
The outlook for Burrowing Owls in British Columbia is reasonably good. Although
habitat loss continues, many other impacts have been minimized,
thanks in part to public awareness and support.
Biology
Burowing Owls are migratory
summer visitors, usually appearing in the Okanagan Valley in April.
The beginning of southward migration is difficult to determine,
but the date of disappearance of adults and young from the nest
site ranges from mid-July to early October. Adult females migrate
earlier than young. Adults usually leave in late July to early August
whereas juveniles usually leave in August to September.
Wintering grounds of British Columbia’s owls are unknown,
but are thought to be south of the United States-Mexico border.
Individuals occasionally seen on the south coast of British Columbia
during winter are probably from nests in the Fraser River Delta.
Although Burrowing Owls are known to winter occasionally around
the Strait of Georgia on the Pacific Coast, there is only one winter
record for the Okanagan (1963).
Breeding
Burrowing Owl nests usually are built in abandoned burrows of
Yellow-bellied Marmots, Belted Kingfisher, Striped Skunks, Prairie
Dog, ground squirrels, badgers and occasionally Red Fox. Nests have
even been recorded near White Lake in an old drainpipe and in a
natural crevice in a railway embankment.
Badger burrows are excellent nest sites because of their location
in bare, open areas without visual obstructions. Nest burrows are
usually 1 to 3 m long, with a downward slope of about 15 degrees,
with a J- or U-shaped bend, and an enlarged nest chamber at the
end. Adults usually return to the same burrow or a nearby area each
year. One or more "satellite" burrows can usually be found
near the nest burrow, and are used by adult males during the nesting
period and by juvenile owls for a few weeks after they emerge from
the nest.
Both sexes prepare the burrow for nesting, using feet, beaks and
wings to scrape out dirt. They often begin these renovations at
several burrows, but select the best one as a nest site. The nest
burrow is lined with horse or cow dung or other material. Researchers
speculate that the lining acts as an absorbent, attracts dung beetles
which are eaten by the owls, masks odours produced by the birds
(making detection by predators more difficult), and/or produces
heat by decomposition, thereby aiding the incubation
of owl eggs.
Six to ten white eggs are laid at the end of the sloping tunnel
and covered with dried horse or cattle droppings. Burrowing Owls
have an incubation period of 28 days and the young emerge from the
nest at two weeks of age. Eggs have been found in May and young
at the beginning of June. The female incubates the eggs for three
to four weeks, while the male brings food to the female during this
period, and stands guard near the burrow by day.
Hatched young stay in the nest chamber for about two weeks. By this time the
young are large, the burrow is very crowded, and they will often
stand at the burrow entrance eagerly waiting food from the parents.
Young birds have been observed outside the nest hole from June to
October. Young owls start to hunt about seven or eight weeks after
hatching but can catch insects on the ground even before they can
fly; Burrowing Owls can fly quite well when only six weeks old.
During this period the female remains near the burrow and helps
to distribute food brought by her mate. Once the young owls are
active above ground, the family may change burrows, minimizing risk
of scent build-up and detection by predators.
Behaviour
Burrowing Owls are most active at night but often hunt during
daylight, mainly in the early morning and late afternoon, especially
when they have young to feed. They may be seen standing at a burrow
entrance throughout the day or sitting on posts and other perches.
The owls have often been reported to nest in loose
colonies. Such groupings may be a response to local abundance of
burrows and food, or an adaptation for mutual defense. Colony members
can alert each other to the approach of predators and join in harassment
of them. During the nesting season, adult males forage over home
ranges 2 to 3 square kilometres in size and the ranges of neighbouring
males may overlap considerably. A small area around the nest burrow
is aggressively defended against intrusions by other Burrowing Owls
and predators.
Capable of producing more than 17 vocalizations, the "primary
song" is given only by adult males when near the burrow to
attract a female. A two-syllable "who-who" is given at
the entrance of a promising burrow. This call is also associated
with breeding, and territory defense. Once a female is enticed to
the site, courtship antics involving various postures, vocalizations,
and displays are undertaken by both sexes, usually within 15 m of
the burrow. Other sounds, called the "rasp," "chuck,"
"chatter," and "scream" are known. Juveniles
give a rattlesnake-like buzz when threatened in the burrow, and
adults give a short, low-level "chuck" call to warn of
approaching predators. This is usually accompanied by bobbing the
head up and down.
Diet or Growing requirements
The entrances to burrowing owl burrows are usually littered with feathers
of small birds, rodent, reptile and amphibian bones and fragments of insects
such as grasshoppers and ground beetles, and even cherry stones. In the
Okanagan Valley, recorded prey items include the Great Basin Pocket Mouse,
Western Harvest Mouse, voles, crickets, beetles, scorpions, and grasshoppers.
On September 27, 1984, 19 pellets found at a nest of introduced owls
at the north end of Osoyoos Lake contained the skulls of 12 Great
Basin pocket mice, the remains of at least 40 sand crickets, 7 ground
beetles, and 1 darkling beetle. Like other owls, this species probably
relies on acute hearing as much as eyesight for capturing prey at
night. Burrowing Owls also collect material (e.g., pieces of cardboard,
scraps of cloth and tufts of cattle hair) and this may be strewn
around the nesting site.
Burrowing Owls daily consume about 15 percent of their body weight.
Undigested food remains (mostly hair, bones, and insect cuticle)
are regurgitated in two or three pellets per day. These pellets
accumulate around the burrow, and provide researchers with an indication
of what has been eaten. The pellets are cylindrical in shape, 3
to 4 cm long and about 1.5 cm thick.
The owls are quite versatile hunters. They chase down grasshoppers
and beetles on the ground, use their talons to catch large insects
in the air, hover in mid-air before swooping down on unsuspecting
prey, or watch patiently from perches, and then glide silently toward
their target.
Predators
Predators, mostly of eggs and young owls, include weasels, skunks,
and snakes. Because Burrowing Owls do not nest in trees, they have
many potential predators. The predators are of two general types:
1) those that enter or dig up burrows to eat eggs, nestlings, and/or
adult females; or 2) those that prey on older nestlings and adults
when above-ground.
In Canada, mammals that can access nest chambers and are potential
predators are: badgers, foxes, striped skunks, weasels, and raccoons.
Species that mainly catch owls above the ground are: coyote, domestic
dog, domestic cat, Swainson's Hawk, Great Horned Owl, Ferruginous
Hawk, Northern Harrier, Short-eared Owl, and Prairie Falcon. Badgers,
skunks, and long-tailed weasels seem to present the most serious
threats to female Burrowing Owls and their eggs in Canada, while
avian predators cause the majority of mortalities in adult males
and fledglings.
Sources for more information
Related On-line Sites to Visit
Publications
The Birds of
British Columbia: The Owls, Guiguet, RBCM, v. 19, 1978.
Birds of the Okanagan Valley, Cannings, 1987
Borealis Issue 11, 1992, p. 18
Our Living Legacy, RBCM, 1993
Status Report, COSEWIC, Wellicome and Haug, 1995
The SOCAP Workshop Summary, The Nature Trust, 1989
Birds of BC, Campbell et al., 1990
Museum Specimens
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BURROWING OWL 