A heterogeneidade do habitat pode afetar diretamente ou indiretamente a disponibilidade de recursos necessários para a sobrevivência e reprodução das aves, uma vez que estas selecionam micro-habitats para forrageamento e sítios reprodutivos. As corujas são aves noturnas que desempenham um importante papel no equilíbrio do ecossistema, por evitar superpopulações de presas e eliminar indivíduos defeituosos. Essas aves são de pouquíssimo conhecimento e principalmente em relação ao uso de habitat. Entretanto, alguns trabalhos mostraram relações entre a distribuição e presença de corujas com características da estrutura da vegetação e com diferentes paisagens. Realizamos um estudo de revisão sobre o status da pesquisa cientifica em relação as corujas e podemos confirmar a carência em estudos com corujas que ocorrem no Brasil. A maior parte das pesquisas relacionadas com esse grupo de aves foram realizadas na América do Norte com apenas a citação de 4 espécies das 21 que ocorrem no Brasil. O tema seleção de habitat, genética e evolução, sistemática e técnicas foram pouquíssimos relatados nas publicações utilizadas nesta revisão. Por outro lado os nossos resultados sobre a influência de algumas variáveis da vegetação em relação à presença de corujas em diferentes fisionomias de Floresta Atlântica, mostraram a importância do uso de micro-habitats na floresta diferenciado por algumas corujas. As diferentes fisionomias da vegetação suportaram assembléias de corujas diferentes e as espécies Corujinha do mato (Ottus choliba), Murucututu da barriga amarela (Pulsatrix koeniswaldiana), Caburé miudinho (Glaucidium minutissimum) e a Coruja do mato (Ciccaba virgata) utilizaram significativamente alguns componentes da estrutura da vegetação. Os nossos resultados sugerem que diferentes fisionomias e estrutura da vegetação influenciam na ocorrência e na variação de espécies de corujas. Isso indica que a estrutura e a densidade da vegetação são importantes para a escolha de alguns tipos de micro-habitats na floresta produzidos por variações na distribuição espacial nos componentes de estrutura e densidade da vegetação. / The habitat heterogeneity can affect directly or indirect resources availability of necessary for the survival and reproduction the birds, a time that these selection micro-habitats for foraging and nest-sites. The owls are nocturnal birds that to play an important role in the balance of ecosystem, for preventing overpopulations of preys and eliminate faulty individuals. These birds were of very little knowledge and mainly in relation to the habitat use. However, some research had show to relations among the owls distributions and presence with characteristics of the structure of the vegetation and different landscape. We carry through a revision study about the status of scientific research in relations the owls and can confirm the really poor of the studies with owls that occur in Brazil. The great part of the research founded had been realized in North American with only the citation 4 species of the 21 that its occur in Brazil. The subject habitat selection, genetc and evolution, systematic and methods are very little related in publications used in this revision. However ours results on the influence among the owls presence with components of the structure of the vegetation in different Atlantic forest physiognomy, showed the importance of the use the microhabitat in the florest. The different physiognomy of the vegetation had supported assemblies of different owls composition of owls and the species Tropical screech-owl, Tawny-browed, Least pygmy-owl, Mottled owl had used significantly some components of the structure of the vegetation. Ours results suggest that different physiognomy and structure of the vegetation influence in the occurrence and variation of the composition of the owls. This indicates that the structure and the density of the vegetation are important for the choice of this habitat in the forest, so that the species can satisfy its biologic cycle and keep its populations.

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

There has been a global decline of specialist species observed in recent decades due to the impacts of climate change, invasive species, and habitat loss. Habitat loss and degradation may lead to a mismatch between habitat attractiveness and actual quality, otherwise known as an ecological trap. Ecological traps occur when an organism is constrained by its evolutionary past to select for cues that no longer accurately predict habitat quality. Specialist species are more susceptible to ecological traps due to greater reliance on and fidelity to historic sites and resources. The burrowing owl (Athene cunicularia), a specialist bird species adapted to open ecosystems, has declined throughout its extent. Anthropogenic activity has drastically and rapidly altered burrowing owl native habitat, exposing their habitat to disturbances such as cheatgrass (Bromus tectorum) invasion. The presence of cheatgrass is known to impact the biota of a region and understanding those impacts is becoming increasingly important. The purpose of this study was to quantify the impact of cheatgrass on burrowing owl populations. By assessing how cheatgrass influences the resource selection, nesting success, and food habits of burrowing owls, we provided information that can be utilized to make more informed decisions on how to conserve burrowing owls and their critical nesting habitat. In addition, this information can provide insight into the risk of ecological traps occurring to all specialist species experiencing degradation of their native habitat.