Treesearch

Monthly visits to Lanyu Island have been made to study Lanyu Scops Owls (Otus elegans botelensis) since 1986. This population has been surveyed by regular census and playback counts, by color banding, by monitoring the survival, reproduction and movements of individual owls, and by mapping and documenting the change in nest trees.

Tail-mounted radio transmitters were attached to 12 juvenile and 3 sub-adult (yearling) Mexican Spotted Owls (Strix occidentalis lucida) in southwestern New Mexico from 1993 to 1996. Most juveniles dispersed from their natal territories during September. Intervals between dispersal of siblings ranged from 3 to more than 15 days. Juveniles exhibited two types of dispersing behavior; moving rapidly across the landscape (up to 11.3 km/night) and extensive local exploration. Two juveniles moved between separate mountain ranges and crossed at least 25 km of grassland and pinon/ juniper (Pinus/Ju...

A Habitat Suitability Index (HSI) model was developed for the Barred Owl (Strix varia) in southeastern Manitoba. An initial validation of the model was performed within three sizes of circular plots (314, 1,256, and 2,827 ha) centered on 28 Barred Owl locations. The model was able to predict suitable habitat at the 314 ha scale. Forest habitat characteristics within the 314 ha plots were described to suggest improvements to the model's performance. The observed values of the three forest resource inventory variables used in the HSI model; cutting class, crown closure, and tree species...

Between 1994 and 1996 we located 15 active Barred Owl (Strix varia) nests in the boreal forest of central Saskatchewan, Canada. Eighty-seven percent of Barred Owl nests were located within old mixedwood forest stands. Nest tree species included white spruce (Picea glauca), trembling aspen (Populus tremuloides), balsam poplar (Populus balsamifera), and white birch (Betula papyrifera). The majority of nests were within natural cavities (67 percent), and the majority of nest trees were live (67 percent). Nest trees were of large diameter, averaging 47.4 cm. Nest site availability appears to...

The ecology and behavior of non-territorial owls are basically unknown. I studied the integration of young Great Horned Owls (Bubo virginianus) into the territorial breeding population from 1988-1993 in the southwestern Yukon, Canada, during a peak and decline of the population cycle of snowshoe hares (Lepus americanus). Fifty-five fledglings were equipped with radio-transmitters that allowed weekly monitoring of individuals for 2-3 years.

Barred Owl (Strix varia) nests are often very difficult to locate. We developed a method for locating Barred Owl nests within the boreal forest of central Saskatchewan, Canada. During the nesting period, we located pairs of Barred Owls through call-playback surveys. We returned to the survey location at sunset and listened for vocalizations from the pair. These vocalizations often occurred near the nest, providing an estimate of its location. The following day, prospective-looking nest trees in the area were hit with a stick in order to flush the incubating owl. We searched for seven nests...

Breeding of the Barn Owl was studied from 1990-1992 in the Lower Mainland of British Columbia, the northern limit of the species' North American range. Over 3 years, mean clutch size was 6.5 ± 3.5, mean brood size at time of banding was 3.3 ± 2.0, and mean number of nestlings fledged was 2.6 ± 2.1. Clutch size ranged from 2 to 18 eggs. There were no significant differences in fledging success rates between years. Severe weather in 1991 resulted in high Barn Owl mortality. If the number of nestlings banded per year is used as an index of productivity and the number of barn owl carcasses...

Stable isotope ratio analysis (SIRA) was used to analyze the trophic level of the diets of three owl species: Barred Owl (Strix varia), Northern Hawk Owl (Surnia ulula) and Great Horned Owl (Bubo virginianus). Barred Owl and Northern Hawk Owl had diets from a similar trophic level. Both the Barred Owl and Northern Hawk Owl had diets from trophic levels that differed significantly from that of the Great Horned Owl. Great Horned Owl had the most diverse isotope ratios indicating the greatest intraspecific variation in diets of the three species of owls. Results of SIRA can help with the...

Great Gray Owls (Strix nebulosa) have been banded and monitored west of Calgary in the foothills of Alberta from 1986 to 1996. Thirty-six adult owls have been banded: 16 males, 16 females and 4 of unknown sex. Great Gray Owls were captured during every month except August and October although the majority (56 percent) were banded from March-May (n=18). Four birds have been recaptured to date. A male was caught in the same location on 23 March and 9 May of 1986, a female was caught in the same location on 31 May 1987 and 18 November 1989, a female banded on 26 December 1988 was road-killed...

The first studies of nesting Flammulated Owls (Otus flammeolus) established the idea that the species needs ponderosa pine (Pinus ponderosa) forests for breeding. In northern Utah, Flammulated Owls nested in montane deciduous forests dominated by quaking aspen (Populus tremuloides). No pines were present but scattered firs (Abies and Pseudotsuga spp.) were on the study plot and groves of firs existed nearby. Using nest boxes, Flammulated Owls nested 34 times in 5 years (1992-1996). Sixty-five percent of nests produced fledglings. Mean clutch size was 2.6 (range 2-4). On average, 2.1 young...