Reintroduction of captive-bred Western Burrowing Owls (Athene cunicularia hypugaea) in the Nicola Valley, British Columbia, has had limited success in increasing the local breeding population. Traditionally, yearling captive-hatched Burrowing Owls that were paired and released into artificial burrows in the field, held overnight, and provided with supplemental food throughout the breeding season (hard release) have had high post-release dispersal and mortality. In 2005 and 2006, I used an alternative soft-release technique to test for an improvement upon the hard-release technique. The soft release followed the same procedure as the traditional hard release but also included enclosures around burrow entrances to contain the owls for a 2-week period in the field prior to release. I compared immediate post-release dispersal, seasonal survival, and reproductive success for 37 hard-released and 30 soft-released pairs. I radio-tagged 39 of these released owls in order to accurately monitor their activities, regardless of whether they remained at release sites or dispersed. The soft-release technique led to 20% more owls remaining at the release sites, 14% more owls surviving the breeding season, and 20% more owl pairs fledging juveniles. In addition to investigating adult survival and reproductive success, I examined post-fledging juvenile survival, local recruitment, and habitat use, and adult prey consumption behaviour in order to assess the potential of these aspects to limit the success of the reintroduction. Survival and local recruitment rates of the juveniles of captive-bred adults released with two different techniques were similar to that of juveniles of wild adults in the same study area or in other parts of the Burrowing Owl's range. Juvenile habitat-selection analyse sidentified the importance of rangeland, and comparisons of prey consumption revealed the rapid development of foraging abilities by captive-bred Burrowing Owls. I concluded that these aspects of the owl's ecology were not negatively affected by a captive upbringing, and therefore not likely limiting the success of the reintroduction. Overall, the use of an enclosure-based soft-release technique addresses major limitations to the success of releases, and shows promise for increasing the breeding population in this region. This approach can also be applied to recovery efforts throughout the Burrowing Owls' range, and provide guidelines for other species' reintroduction programs. / Land and Food Systems, Faculty of / Graduate

During the 1979 breeding season four pairs of northern harriers, or marsh hawks (Circus cyaneus) and four pairs of short-eared owls (Asio flammeus) were studied in Cache Valley, Utah. The study was concerned solely with diurnal resource utilization, and did not examine the owls' nocturnal activities. The home range of each harrier pair overlapped substantially with that of an owl pair. Percent habitat overlap for hawk-owl pairs varied from 39 percent to 72 percent. Observations were made to determine if differences existed in their utilization of habitat and food resources, or in their daily and seasonal activity patterns. Both species utilized mainly wet old field and pasture habitat types for their hunting efforts. In general wet old fields were utilized more than expected based on their availability, while pasture, bare ground, and harvested field habitats were used less than expected. Pairs of hawks and owls sharing common habitats generally showed differences in preferred hunting habitats. An analysis of variance showed that hawks and owls were making strikes in different habitat types and to some extent in different parts of the habitat. Harriers and owls nested in different habitat types. Breeding seasons of the two species overlapped almost totally, but interspecific differences were detected in time-activity budgets. Overall, the owls were more sedentary than the hawks. Both species spent approximately 10 percent of the day in hunting-related activites, but timing of hunting varied from pair to pair. Overlapping pairs generally differed in their daily distribution of hunting time. The analysis of variance showed that there was a significant difference in the timing of strikes made by harriers and owls. Both species were feeding primarily on small mammals in the study area, and food resources were probably not a limiting factor for either population. Though northern harriers and short-eared owls appear to have a high degree of niche overlap, this study showed that where eight individual pairs of the two species came into contact they differed in time-activity budgets and habitat utilization. Coexistence between these two species may be enhanced by the fact that they both feed on an abundant prey resource. By subtle habitat and time budget preferences, reinforced through interspecific aggression, they can avoid competition.

No description available.

A review of energetics studies of raptorial species introduces four separate studies of temperature regulation by raptors. Golden Eagle (Aquila chrysaetos) nest site selection, as influenced by direction of exposure, is discussed. The data show strong directional preferences to the NNW by southern populations and SSE by northern populations. The tarsometatarsus is shown to have a thermoregulatory function in large falcons, and adaptations of this mechanism to varied habitats are examined. Color phase in Screech Owls (Otus asio) is shown to be related to metabolic differences that may explain the distributions of the color morphs. Development of thermoregulation in Flammulated Owls (Otus flammeolus) is examined.

Durante la época lluviosa del año 2010 y la época seca del año 2011 fue examinada la composición de especies de lechuzas en la Vertiente Pacífica de Costa Rica. Se utilizó el método de estimulación con vocalizaciones coespecíficas para estimar la composición, frecuencia de detección y abundancia relativa de especies de ensamblajes de búhos y lechuzas en tres núcleos de bosque tropical secundario distribuidos en un rango de 0 m hasta 2100 m. El estudio se basó en la clasificación de zonas de vida desarrollado por Holdridge. Se registraron un total de siete especies de aves rapaces nocturnas. Se colocaros 16 puntos de muestreo en dos senderos de cada núcleo de bosque, ocho puntos por sendero. Los tres sitios variaron en cuanto a la riqueza de especies detectadas y esperadas. Las diferencias no fueron significativas entre los núcleos durante la época lluviosa, sin embargo para Strix nigrolineata y Strix virgata si hubieron diferencias durante la época seca. La similitud de especies fue mayor entre los núcleos de alturas menores, y más baja entre el bosque de tierras bajas y el bosque de tierras altas. La frecuencia de detección varía entre especie y entre núcleos de bosque, siendo Strix virgata la lechuza con mayor frecuencia de detección en tierras bajas e intermedias, y mayor abundancia en los tres núcleos de bosque. Por el contrario Lophostrix cristata tuvo menor frecuencia de detección y menor abundancia en dos de los tres núcleos de bosque estudiados durante la época lluviosa. No se detectó ningún individuo de Pulsatrix perspicilata dentro de los puntos de muestreo durante la época lluviosa, sin embargo fuera de los puntos si hubo registros / During the rainy season of 2010 and the dry season of 2011, We examined the composition of owl species within in the Pacific Slope of Costa Rica. We employed the playback survey method using conspecific vocalizations of owl species to estimate their composition, frequency of detection and relative abundance of owl species in three secondary tropical stands of forest distributed from sea level to 2100m. The study was based on the classification of life zones developed by Holdridge. A total of seven owl species were detected. We set up 16 points in two trails at each forst fragment, eight points per trail. The detected and expected species richness was different at the three forest fragments. While differences were not significant, the three stands differed in species richness; nevertheless there were differences in the dry season for Strix virgata and Strix nigrolineata, with a greater overlap of owl species among the middle/lower forest areas, and lower among the lowland forest and upland forest. The detection rate varied between species and between forest stands, with Strix virgata detected most frequently in the lowlands and intermediate lands, and with higher abundance than other owls in the three stands of forest. By contrast, Lophostrix cristata had lower frequency of detection and lower abundance in two of the three studied forests during the rainy season. We found no Pulsatrix perspicilata individuals within the sampling sites in the rainy season, however there were records outside the sample areas

Durante la época lluviosa del año 2010 y la época seca del año 2011 fue examinada la composición de especies de lechuzas en la Vertiente Pacífica de Costa Rica. Se utilizó el método de estimulación con vocalizaciones coespecíficas para estimar la composición, frecuencia de detección y abundancia relativa de especies de ensamblajes de búhos y lechuzas en tres núcleos de bosque tropical secundario distribuidos en un rango de 0 m hasta 2100 m. El estudio se basó en la clasificación de zonas de vida desarrollado por Holdridge. Se registraron un total de siete especies de aves rapaces nocturnas. Se colocaros 16 puntos de muestreo en dos senderos de cada núcleo de bosque, ocho puntos por sendero. Los tres sitios variaron en cuanto a la riqueza de especies detectadas y esperadas. Las diferencias no fueron significativas entre los núcleos durante la época lluviosa, sin embargo para Strix nigrolineata y Strix virgata si hubieron diferencias durante la época seca. La similitud de especies fue mayor entre los núcleos de alturas menores, y más baja entre el bosque de tierras bajas y el bosque de tierras altas. La frecuencia de detección varía entre especie y entre núcleos de bosque, siendo Strix virgata la lechuza con mayor frecuencia de detección en tierras bajas e intermedias, y mayor abundancia en los tres núcleos de bosque. Por el contrario Lophostrix cristata tuvo menor frecuencia de detección y menor abundancia en dos de los tres núcleos de bosque estudiados durante la época lluviosa. No se detectó ningún individuo de Pulsatrix perspicilata dentro de los puntos de muestreo durante la época lluviosa, sin embargo fuera de los puntos si hubo registros / During the rainy season of 2010 and the dry season of 2011, We examined the composition of owl species within in the Pacific Slope of Costa Rica. We employed the playback survey method using conspecific vocalizations of owl species to estimate their composition, frequency of detection and relative abundance of owl species in three secondary tropical stands of forest distributed from sea level to 2100m. The study was based on the classification of life zones developed by Holdridge. A total of seven owl species were detected. We set up 16 points in two trails at each forst fragment, eight points per trail. The detected and expected species richness was different at the three forest fragments. While differences were not significant, the three stands differed in species richness; nevertheless there were differences in the dry season for Strix virgata and Strix nigrolineata, with a greater overlap of owl species among the middle/lower forest areas, and lower among the lowland forest and upland forest. The detection rate varied between species and between forest stands, with Strix virgata detected most frequently in the lowlands and intermediate lands, and with higher abundance than other owls in the three stands of forest. By contrast, Lophostrix cristata had lower frequency of detection and lower abundance in two of the three studied forests during the rainy season. We found no Pulsatrix perspicilata individuals within the sampling sites in the rainy season, however there were records outside the sample areas