Observations on the breeding ecology of burrowing Owls in Saskatchewan
Abstract
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.