Treesearch

During a long-term Great Horned Owl (Bubo virginianus) banding program, 1946-1996, there were opportunities to band 507 Long-eared Owls (Asio otus) and 246 Short-eared Owls (Asio flammeus). No less than 35.1 percent of the Long-eared Owls and 63.5 percent of the Short-eared Owls were banded in two unusual years, 1960 and 1969, after Microtus had proliferated under swaths of grain that lay unharvested beneath the snow. Such numbers are strong but not conclusive support for nomadism. Five Long-eared Owls were recovered (1 percent of bandings) but no Short-eared Owls, and there have been no...

During 1993-1997, three adjacent nesting pairs of the Southern Boobook (Ninox novaeseelandiae) were located and observations made on their behavioral interactions, nests, and young in Canberra, Australia. Territory size was close to 100 ha; not the 4 to 10 ha reported in the literature. Males advertized territorial boundaries with the "boobook" call and 'duelled' using this and a "croaking" call. Neighboring males entered a rival's territory to challenge the resident male, sometimes near the resident's nest. Both sexes fed the young until 2 to 4 weeks after fledging, when females stopped....

Multiple logistic regression analysis was used to produce a prediction model for Flammulated Owl (Otus flammeolus) breeding habitat within the Kamloops Forest Region in south-central British Columbia. Using the model equation, a pilot habitat prediction map was created within a Geographic Information System (GIS) environment that had a 75.7 percent classification accuracy. Factors were identified indicating the quality of the modeling process; several limitations were also detected. Maps derived from the pilot model will be ground-truthed in coordination with field inventories. New habitat...

During the autumn of 1995 more than 5,900 migrant Northern Saw-whet Owls were banded in eastern and central North America. Though typical numbers of owls were banded at most Great Lakes stations during 1995, a record number were netted at Hawk Ridge, near Duluth, Minnesota and, when compared with more normal years, a remarkably disproportionate 40 percent of the total were banded at 5 stations in New Jersey, Maryland, and Virginia. The movement occurred throughout the eastern U.S. and may have been comparable to that of 1965 when unusually high numbers of Northern Saw-whet Owls were netted...

Using a hormone implant protocol, we created treatment groups in which circulating levels of testosterone (T) were increased, decreased, or maintained at normal levels (controls) in male Western Screech-owls (Otus kennicottii). Owls were exposed to tape-recorded vocalizations of a conspecific, to which territory holders responded with aggression. Several measures of the intensity of aggression (e.g., approach and vocal behavior) provided the basis for comparisons among treatment groups. Exogenous T elicited increased aggression during the breeding and nonbreeding seasons. Although male...

Prey use by Great Horned Owls (Bubo virginianus) is documented widely in North America, but not in the vast northern Great Plains. During spring through early summer 1986-1987, I recorded 2,900 prey items at 22 Great Horned Owl nesting areas in the prairie pothole farm- and rangelands of northwestern North Dakota. The owls relied heavily on wetland-dependent prey species (overall, 57 percent by number and 76 percent biomass) especially ducks (Anserinae) and rails (Rallidae). Far more avian (65 percent by number and 84 percent biomass) and less mammalian prey were used than typically...

During 1963-1996, 1,101 Barn Owl (Tyto alba) carcasses were received for autopsy and chemical analysis. Much larger numbers were received per month outside the breeding season than within it. A peak in the monthly mortality of first year birds occurred in autumn (November) and a peak in the mortality of adults in late winter (March).

Broadcast surveys are used to determine the presence and relative abundance of nocturnal owls, but there has been little effort to standardize such surveys. This paper examines broadcast survey data collected in 1995 and 1996 in the Foothills Model Forest, Alberta, Canada. Three hundred calls from six species of owls were recorded at 893 stops for a call rate of 0.34 calls per stop. Moon phase significantly affected the rate of owls calls. Owl call rate was significantly lower in the middle of the night (midnight to 3:59) compared to the early night (20:00 to 23:59) and early morning (4:00...

Belthoff and Dufty (in press) posed a model for dispersal in screech-owls and similar nonmigratory birds. The model is based on interactions among hormonal changes, body condition, and locomotor activity patterns. It predicts that corticosterone increases in blood plasma prior to dispersal under endogenous and exogenous influences, and this increase mediates the locomotor activity that underlies dispersal. Juveniles in good body condition (i.e., those with sufficient fat reserves) will disperse at that time, while birds in poor body condition will not. The latter will increase their...

We examined dispersal distance of young Western Screech-owls (Otus kennicottii) from nest sites to overwintering sites in relation to two hypotheses for sex-biased dispersal. Overall, young Screech-owls (N = 31) dispersed an average of 10.6 ± 1.8 km to overwintering sites, and females (14.7 ± 2.5 km; N = 13) dispersed farther than males (5.1 ± 2.3 km; N = 15). This result is not consistent with the behavioral dominance hypothesis, which predicts that individuals of the more dominant sex class (apparently females in Western Screech-owls) should be more philopatric. The mating system...