Observations on the breeding ecology of burrowing Owls in Saskatchewan
Haug, Elizabeth Anne
Observations regarding breeding biology of burrowing owls (Athene cunicularia) were collected on 98 breeding pairs during 1982 and 1983. Pairs of owls were first observed on the study area in late April with clutch initiation beginning in mid-May. Overall nest success averaged 59 percent with 2.6 young fledged per nest attempt. Pairs nesting on tame pasture had a higher nest success and a greater number of young fledged per nest attempt. It was believed that predation pressure was greater for those pairs nesting on native pasture, which caused more nest failures and higher nestling mortality. Vehicle collision accounted for 37 percent of the known morta1ity. Predation accounted for 41 percent, a1though it can be assumed that most victims of predation were never recovered. Loss of breeding habitat and lack of burrow availability is believed to represent major threats to burrowing owl populations. Organochlorides recovered from owl carcasses included DDT, DDD, DDE and heptachlor epoxide. Toxic chemicals represent a possible unknown cause of breeding failure or morta1ity. Food habits were determined from 178 pellets. Overall, arthropods comprised 93 percent and vertebrates 7 percent of total numbers of prey items identified. Small mammals dominated the prey items utilized in May and early June with grasshoppers (Acrididae) being taken during July and August. Problems inherent in food habit studies are discussed. Home range, activity patterns and foraging habitat utilization was determined with the aid of radio-telemetry. Six adult male owls were radio-marked and monitored during the peak foraging periods. Owls selected grass/forb areas more often than other habitat types for foraging. Crop and native pasture were avoided in comparison to their occurrence within the home ranges. Average home range size was 2.41 km2 and ranged from 0.14 to 4.81 km2. Activity patterns were monitored and it was determined that peak foraging hours occurred with long distance flights between 2000 and 0630 hours. Management implications and recommendations are discussed.