Wildlife At Risk in British Columbia A brochure series which will eventually include brochures on other Red and Blue listed species, including fish, invertebrates and plants, and on ecosystems. Produced by the Ministry of Environment, Lands and Parks, Wildlife Branch, 780 Blanshard St. Victoria, BC V8V 1X4. For copies of this brochure, write to the Wildlife Branch. Funded by Corporate Resource Inventory Initiative and Ministry of Environment, Lands and Parks. ________________________________________________________________ The Burrowing Owl’s remnant habitat of natural grassland is being diminished by expanding towns and intensive agriculture Why are Burrowing Owls at risk? This diminutive owl has a very restricted distribution and small population in British Columbia. Although never large, the population dwindled during this century, and from 1928 to 1980 evidence of breeding was reported from only four areas in the southern interior of the province. The overall abundance of Burrowing Owls is limited by 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. A serious problem is that the small area of natural grassland is being further diminished by expanding towns, intensive agriculture, and a multitude of other industrial uses and developments, especially in the Okanagan Valley. As well, there appears to be a shortage of burrowing animals in habitats that are also suitable for the owls. This may be a result of ground squirrel and Badger control by agricultural interests, or other mortality factors affecting those mammals. Humans have contributed to Burrowing Owl mortality in many parts of their range. Some owls, particularly naive juveniles feeding on road-kills or on insects attracted by warm pavement at night, 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. Use of crop pesticides may also reduce the abundance of important prey, such as grasshoppers and mice. In past years, agricultural chemicals such as ddt may have adversely affected Burrowing Owl reproduction. It is not known how significant these factors presently are in British Columbia. Burrowing Owls also have to contend with many natural hazards, such as predators and weather-caused mortality. However, the addition of human-caused mortality and habitat degradation has caused population declines in many areas. What is their status? Because of its low numbers and restricted distribution, the Burrowing Owl has been placed on British Columbia’s Red List and is also legally designated under the Wildlife Act as an Endangered Species. Although information on historical occurrence of Burrowing Owls in British Columbia is limited, we know that there were several small nesting colon-ies present in the Okanagan and Thompson valleys from 1900 to 1928. Numbers dwindled after that, with only four nesting sites being recorded between 1928 and 1980, at which time they were thought to be extirpated as a breeding species in the province. Historical nesting areas include Osoyoos, Oliver, Penticton, White Lake, low-er Similkameen Valley, Cold-stream, Okan-agan Landing, Knutsford, Savona, Kamloops and Douglas Lake. As well, one or two pairs nested at Lulu Island in the Fraser Delta during most years from 1939 through 1976. Stragglers, probably non- breeding, have been seen intermittently 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 population status of Burrowing Owls in British Columbia improved through the 1980s, when about 500 individuals were transplanted, mostly from Washington State (see “What can we do?”). Elsewhere in Canada, Burrowing Owls breed only across the grassland region of the prairie provinces, where there are an estimated 2000 breeding pairs. The prairie population has been declining since at least 1930 due to grassland cultivation, pesticide use, traffic mortality, and related factors. Recent declines in eastern Saskatchewan and in Manitoba are particularly alarming. The species is nationally designated as “Threatened” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Burrowing Owls have a wide distribution outside of Canada, occurring in all states west of the Mississippi Valley, in Florida, and south into Mexico, Central America and South America. Populations have declined in many areas due to human-caused habitat loss or alteration. What do they look like? The often comical looking Burrowing Owl (Athene cunicularia) has been aptly described as a short fat owl on stilts. The long, almost bare legs and stubby tail of this plump-looking little owl are indeed distinctive, as is its habit of perching on the ground or on fenceposts. It is similar in size to the American Robin, with a total length (head to tail) of about 24 centimetres. 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 colouring, although males often appear faded, possibly from spending more time exposed to the sun. Adults are a rich sandy-brown colour, thickly spotted with whites and buffs on the upperparts; 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. What makes them unique? Within the owl family, Burrowing Owls are unusual in many respects: they live in underground burrows, in grassland rather than forest, are often active in broad daylight, and eat insects as well as rodents. These are adaptations for life in a grassland environment. The focus of activity for this owl is the burrow. Its main use is for nesting, but burrows also provide refuge from many predators and protection from extreme heat or cold, and are used in any season. Although capable of digging their own burrows in suitable soils, in British Columbia Burrowing Owls prefer to modify abandoned burrows of Badgers, ground squirrels, or marmots. 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. Burrowing 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 defence. 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. Burrowing Owls are often seen standing about in daylight, giving rise to the belief that they are largely active during the day. However, recent radiotracking studies indicate that most hunting activity occurs from dusk to sunrise. Daytime activity mostly involves loafing within 50 metres of the nest or a satellite burrow, although some daytime feeding by juveniles occurs near the burrow when insects become abundant in late summer. An amazing repertoire of about 17 vocalizations has been described for Burrowing Owls. The “primary song,” given only by adult males when near the burrow, is a two-syllable “who – who”. This call is associated with pair formation, breeding, and territory defense. Other sounds, called the “rasp,” “chuck,” “chatter,” and “scream” have been described. 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. An endearing feature of Burrowing Owls is their tolerance of non- threatening human activity. Nests are sometimes found in cow pastures near farm buildings, on airports, or on road rights-of-way. This tolerance, together with their habit of loafing around the nest burrow or on fenceposts in daylight, make this one of the most observable of all owl species. Most Burrowing Owls that occur in British Columbia during summer migrate south for the winter. They have been recorded in the Okanagan Valley in early March, but the majority arrive in April. Autumn migration is a gradual process extending from July to October. Wintering locations of birds from the interior are not known. The individuals occasionally seen on the south coast of British Columbia during winter are probably from nests in the Fraser River Delta. How do they reproduce? Recorded nesting sites in British Columbia include burrows of the Yellow- bellied Marmot, Badger, Striped Skunk and Belted Kingfisher, a natural crevice in a railway embankment and an old drain pipe. Nest burrows are usually 1 to 3 m long, with a downward slope of about 15 degrees, 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. Pair formation is believed to begin when the owls arrive at their nest sites. Males try to attract a female with their “primary song,” which is given at the entrance of a promising burrow. 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. Both sexes prepare the burrow for nesting, using feet, beaks and wings to scrape dirt out of it. They often begin these renovations at several burrows, eventually selecting the best one as a nest site. This is then lined with horse or cow dung or other material. It has been speculated that the lining material acts as an absorbent, attracts dung beetles eaten by the owls, masks odours produced by the birds (making detection by predators more difficult), or produces heat by decomposition, aiding in the incubation of the eggs. Egg-laying in interior British Columbia begins in late April and early May, but may be earlier on the coast. The clutch consists of six to ten white eggs. The female incubates the eggs for three to four weeks. The male brings food to the female during incubation, 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 for the parents to bring food. The young owls begin flying at four weeks and can fly quite well when six weeks old. They start to hunt for themselves seven or eight weeks after hatching, but can catch insects on the ground even before they can fly. During this period the female remains near the burrow and helps to distribute food brought in by her mate. Once the young owls are active above ground, the family often uses several burrows in the immediate area. What do they eat? The staple foods of Burrowing Owls throughout their range are mice and in-sects, although they will eat other things if available. Remains of a variety of small birds, reptiles, amphibians, fish, and crustaceans have been recorded at nest sites in the United States. In the Okanagan Valley, recorded prey items include the Great Basin Pocket Mouse, Western Harvest Mouse, voles, crickets, beetles, scorpions, and grasshoppers. Like other owls, this species probably relies on acute hearing as much as eyesight for capturing prey at night. Burrowing Owls daily consume about 15 percent of their body weight. Undigested food remains (mostly hair, bones, and insect parts) are regurgitated in the form of two or three pellets per day, and these accumulate around the burrow, providing an indication of what has been eaten. The pellets are cylindrical in shape, 3 to 4 cm long and about 1.5 cm thick. Burrowing Owls are versatile in the ways they capture prey. They chase down grasshoppers and beetles on the ground, use their talons to catch large insects in the air, or hover in mid-air before swooping down on unsuspecting prey. They also watch patiently from perches, then glide silently toward their target. Where do they live? The major habitat needs of Burrowing Owls are prairie-like terrain with low herbaceous vegetation, deep soil for burrows, the occurrence of mammals that excavate burrows, and a food supply. Burrowing Owls are adapted to open, usually dry country with short vegetation. Being ground-dwellers, it is difficult for them to detect approaching predators or find prey in brushland or forest. They are well adapted to grazed rangelands, but find croplands less suitable. The terrain is often flat, but rugged landscapes are also used. The extent of suitable habitat is quite restricted in British Columbia. Over much of its North American range, this owl is most abundant in active colonies of ground squirrels or prairie dogs, where numerous nesting and satellite burrows are available. This indicates that the availability of burrows is a major factor controlling the abundance of Burrowing Owls. Burrows dug by Badgers are also important in many areas. In British Columbia there are relatively few burrowing mammals in habitats that are otherwise 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 disturbing them. What can we do? An ambitious BC Environment program to increase Burrowing Owl abundance in British Columbia, financially supported by the Habitat Conservation Fund, began in 1983. Thanks to outstanding cooperation from Washington State wildlife officials, 82 adults and 348 juveniles (about three weeks old) were transplanted as family units from Wash- ington to recovery areas near Vaseux and Osoyoos lakes from 1983 to 1990. Broods were plac-ed in artificial burrows made from plastic pipe (donated by Big-O Inc.), with an inverted bucket at the end for a nest chamber. Adult owls showed a strong attachment to their broods and continued to care for them despite the disruption of the move. The program also included construction of satellite burrows to provide cover for adult males and to give the developing young space to spread out. The South Okanagan recovery program has been initially encouraging. During the years 1986 through 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 at the Owl Rehabilitation Centre in Ontario. The long-term success of these programs is dependent on whether self-sustaining populations are established. Emphasis of the Burrowing Owl recovery program is now on captive breeding in wildlife rehabilitation centres, including Stanley Park in Vancouver and the Kamloops Wildlife Park. Captive-bred owls will mostly be released as yearlings, thus avoiding the high mortality faced by hatchlings in the wild. Accompanying research on habitat quality, prey abundance, fledging success, and return rates is underway. The long-term goal of BC Environment 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 program is part of the National Recovery Plan developed in cooperation with Alberta, Saskatchewan, Manitoba, the Canadian Wildlife Service (CWS), and the World Wildlife Fund. The outlook for Burrowing Owls in British Columbia is reasonably good. Although habitat loss is an on-going problem, many human-caused impacts are lower now than in earlier years. With public support, these curious little ground-owls may become firmly and permanently established in our southern grasslands.