Thesis (M.S.)--Oregon State University, 2004. / Includes bibliographical references (p. 94-97). Also available via the World Wide Web.

Thesis (M.S. in environmental science)--Washington State University, August 2009. / Title from PDF title page (viewed on Sept. 17, 2009). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 35-42).

Thesis (M.S.)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Mark Taper. Includes bibliographical references.

I used a comparative and experimental approach to examine nest habitat selection, reproductive success, and nest site fidelity of burrowing owls (Athene cunicularia) in a large, non-fragmented grassland in southwest California. In 1999, I compared habitat characteristics between nest sites (n = 31) and randomly selected, unoccupied burrows (n = 31) in the local vicinity of the nest (paired burrows). In 2000, I compared habitat characteristics between nest sites (n = 33) and randomly selected, unoccupied burrows (n 32) within the study area (unpaired burrows). I examined reproductive success and variation in nest habitat characteristics, diet quality, and intraspecific competition using data from 1998, 1999, and 2000. I experimentally (n = 11 control and 11 treatment nests) assessed the effect of satellite burrow (multiple auxiliary burrows near the nest) use on productivity and behavior. I found little variation in habitat between nest sites and unoccupied burrows. Habitat selection was not strong when nests and unoccupied burrows were spatially correlated (paired burrows). However, nest sites had a larger number of large diameter burrows, satellite burrows, and perches than the unpaired burrows. Nest success ( I young fledged) and productivity (the number of young alive at 14 -21 days) varied substantially among some years, though the habitat variables I tested did not explain reproductive success when both failed and successful nests were evaluated. When nests were successful, productivity was influenced by rodent consumption. Nest fidelity within the breeding season was highly correlated with nest success. Nest abandonment occurred at 83% (n = 15 of 18), 92% (n = 12 of 13), and 83% (n = 20 of 24) of the failed nests in 1998, 1999, and 2000, respectively. Results of the experimental manipulation of satellite burrow access showed that productivity did not differ between groups but demonstrated that burrowing owls will adjust their behavior to use satellites. Owls in the treatment group (71%; n = 5 of 7) responded by moving their families to areas with access to satellite burrows but none of the control group owl families moved. This study illustrates the importance of identifying critical factors affecting reproductive success of burrowing owls in large grasslands. Maintenance of burrowing mammal populations to provide nest and satellite burrows will be important for protecting burrowing owls. Also, temporal dynamics influenced reproductive success. Habitat characteristics that enhance foraging ability may benefit productivity, especially in years of low rodent numbers. Furthermore, temporal variation in nest success may lead to low nest site fidelity. / Graduation date: 2002

Large burrowing owl (Aihene cunicularia) populations exist in areas of intensive agriculture in California, and pesticide exposure has been identified as a potential threat to population persistence. I evaluated breeding season use of agricultural fields by adult male owls using radio telemetry, and examined egg contaminant residues to estimate population-level effects on reproduction and survival. Reproduction and survival were estimated annually, and an index of diet was inferred from pellet samples. A total of 11 adult males in 1998 and 22 in 1999 were successfully radio-tracked. Mean fixed kernel home range sizes were 172 ha (SE=68) in 1998 and 98 ha (SE=16) in 1999. Pellet analyses indicated a substantial increase in the numbers of rodents consumed in 1999, associated with an observed population explosion of California voles (Microtus calfornicus). Distance to the nest was the most important factor in differentiating between foraging and random locations, and there was no tendency to select or avoid any cover type. Owls did forage in agricultural fields, but I failed to find evidence of selection or avoidance of fields recently treated with pesticides. A total of 92 eggs were collected over 5 years. Egg contaminants were generally limited to the presence of p,p'DDE, which fluctuated by 4 orders of magnitude among years, from 0.05 ug/g to 33 ug/g fresh weight p,p'DDE. There was a general pattern of decline in egg residues over time for individual birds. The levels of p,p'DDE I documented did not appear to have any effect on either productivity or survival of adult females, nor were they clearly related to diet. I modeled the effects of various pesticide exposure impacts on demographic rates and determined that exposure rates based on field data would lead to relatively minor declines in population growth rate. An elasticity analysis of burrowing owl demographic parameters revealed a variable pattern, but generally indicated that factors influencing anyone of the demographic parameters of burrowing owls can have a substantial impact on population growth rate. / Graduation date: 2002

Recent observed changes in bird distributions provide an unprecedented opportunity to gain a deeper understanding of the processes that influence species' persistence. By modelling presence-absence data from the North American Breeding Bird Survey, we found evidence that the breeding range of the western burrowing owl has contracted at its northern, western, and eastern boundaries since 1967. We suggest that the species' breeding distribution is also expanding southwards to former wintering grounds into northern Mexico, facilitated by the appearance of new breeding habitat created by irrigated agriculture in the arid areas of southwestern United States and northwestern Mexico. This dissertation explores the hypothesis that burrowing owls from northern migratory populations have become resident breeders in areas of northwestern Mexico that were formerly used only by migratory owls during winter, contributing to both population declines near the northern extent of the species' breeding range and population increases in the southern half of the species' range. We used novel DNA microsatellite markers to test patterns of gene flow predicted by this migration-mediated range-shift hypothesis. We genotyped 1,560 owls from 36 study locations in Canada, Mexico, and the United States. Analyses of molecular variance provided evidence that burrowing owl populations in both northwestern Mexico and Canada are genetically different from the rest of the populations in the breeding range, lending some support to the migration-mediated range-shift hypothesis. We found evidence of subtle genetic differentiation associated with subtropical irrigated agricultural areas in southern Sonora and Sinaloa, demonstrating that land use can produce location-specific population dynamics leading to genetic structure even in the absence of dispersal barriers. We also used stable isotopes 2/H, 13/C, and 15/N in feathers to test philopatry and breeding dispersal patterns predicted by this migration-mediated range-shift hypothesis. Burrowing owl populations near the northern edge of the species' breeding range had a high proportion of immigrants compared to interior populations, while other populations had high levels of philopatry. Stable isotopes also provided evidence of breeding dispersal events from Canadian populations to northwestern Mexico in support of the migration-mediated range-shift hypothesis, but similar isotope signatures in nestling feathers between these two regions prevent stronger inferences.

O cerrado é a maior, mais rica e provavelmente a mais ameaçada savana tropical do mundo. No entanto, grande parte de sua área foi ocupada por empreendimentos de agropecuária, nos quais não foram respeitados princípios básicos de conservação, sendo que cada grupo ou táxon reage de forma diferente a mudanças ambientais desse tipo. As aves de rapina, como os Falconiformes e os Strigiformes, são especialmente prejudicadas, pois são considerados predadores de topo de muitas teias alimentares. Porém, para saber como essas aves são afetadas pelas mudanças ambientais causadas pela ação do homem é necessário entender quais fatores são relevantes na \"escolha\" do ambiente de determinada espécie e assim compreender a razão de uma possível seletividade de hábitat. Sendo assim, o presente estudo observou características ecológicas de duas espécies de corujas comuns e bem distribuídas no Brasil, Megascops choliba e Athene cunicularia. Dentre os objetivos estão analisar a metodologia de estudo dessas aves de rapina, com possíveis efeitos na detecção de contatos e verificar o uso de hábitat, em diferentes fisionomias de cerrado, por parte das duas espécies de corujas. O estudo foi realizado na região da Estação Ecológica de Itirapina, no interior do estado de São Paulo. Para contatar as corujas foram realizados experimentos de playback em pontos de amostragem distribuídos em quatro fisionomias (neste estudo consideradas habitats) de cerrado. A atividade vocal de M. choliba variou conforme a temperatura e a umidade relativa. Esta espécie respondeu mais ao playback em condições de temperatura e umidade relativa altas. Athene cunicularia mostrou variar sua atividade vocal conforme a fase da lua e a intensidade do vento. Indivíduos desta espécie respondem mais intensamente ao playback em noites de lua cheia e menos em noites com ventos mais fortes. As duas espécies de corujas se distribuem diferentemente entre as fisionomias de cerrado. Athene cunicularia distribui-se distintamente entre fisionomias fechadas e abertas (Hk-w = 9,976; p = 0,0188), utilizando mais frequentemente as os campos limpo e sujo. Megascops choliba também se distribui diferentemente entre as fisionomias de cerrado (Hk-w = 10,88; p = 2 0,0137), utilizando preferencialmente o campo cerrado e o cerrado s.s.. Segundo os modelos tidos como os melhores, pela seleção de modelos feita através do AIC (Aikaike\'s Information Criterion), a variável com maior poder explicativo é o número de arbóreas para as duas espécies. Megascops choliba e A. cunicularia se segregam ecologicamente, havendo partição divergente de recursos espaciais, devido a seus requisitos para nidificação e forrageamento. Ocorre sobreposição intermediária no uso do habitat entre ambas espécies (O = 0,466). Já quanto a amplitude de nicho espacial (uso de habitat) M. choliba foi generalista (Bst = 0,753) e A. cunicularia intermediária (Bst = 0,453). Sendo assim, estas espécies divergem na seleção de habitat, se distribuindo diferentemente entre as fisionomias de cerrado de acordo com o número de arbóreas. Este estudo sugere, ainda, a importância de se levar em consideração as variáveis climáticas em estudos com o uso de vocalizações de aves de rapina noturnas, servindo também de subsídio para pesquisas futuras sobre censo dessas aves. / The Cerrado biome is the largest, richest and perhaps the most threatened tropical savannah of the world. However, most part of its natural areas has been transformed on agrosystems and pastures where basic principles of conservation weren\'t respected. Each biological group or taxa are affected on different ways by this change. Birds of prey are particularly affected because of its position in trophic webs, as they are top predators. To understand how these birds are affected by change caused by human land use, it is necessary to understand which factors are important for habitat selection, and then understand the species-habitat relationship. Thus, we observed ecological aspects of two widespread and common owls on Brazil: Tropical Screech-Owls (Megascops choliba) and Burrowing Owl (Athene cunicularia). The main objectives of this study included an analysis of methodological aspects of studying these owls species through playback and observe their habitat use. The study was conducted in the Estação Ecológica de Itirapina, State of São Paulo, Brazil. For doing it, we used playback experiments to detect these owls on four different cerrado physiognomies Vocal activities of Tropical Screech-owls were more detected in conditions of higher temperature and humidity. On the other hand, the Athene cunicularia answered more to playback in lower wind speed conditions and/or at full moon nights. The Burrowing Owl explored more frequently open physiognomies of cerrado, as campo limpo and campo sujo (Hk-w = 9.976; p = 0.0188). Conversely, Megascops choliba is more often found on campo cerrado, avoiding campo limpo (Hk-w = 10.88; p = 0.0137). According to Aikaike\'s Information Criterion (AIC) selection model, the most important variable to explain the distribution of both species in cerrado is the number of trees. There was ecological segregation between Megascops choliba and A. cunicularia. The spatial niche was intermediarily segregated (Pianka´s niche overlap measure O = 0.466), according their different needs for nesting and foraging. Additionally, these owls displayed broader (M. choliba Bst = 0.753) or intermediate (A. cunicularia Bst = 0.453) spatial niche breadths. On this sense, these owls have different needs on habitat selection, and their different distributions in cerrado were related more intrinsically to the number of trees present on each physiognomy, which is related to their nesting and foraging requirements. Aditionally, this study suggests, the importance to consider the influence of weather conditions on broadcast survey techniques for nocturnal raptors, which may be considered in further studies on census of these birds.

No description available.

From 1988 to 1990 a study of the reproductive ecology of the burrowing owl was conducted to determine seasonality and reproductive success in Dade and Broward Counties. Reproductive data for each of the three years (1988- 1990) reveal a higher reproductive success rate (54%) for 1990 than 1989 (40%) and 1988 (40%). Owls using previously used burrows had a higher success in fledging young (63%) than newly excavated burrows (19%). T-tests were conducted on several appendage measurements of male and female owls to determine sexual dimorphic traits. Metatarsus lengths of males and females were different (t=2.36, p=0.02). As of 1990,197 owls had been banded in the study area. In 1989, 75% and in 1990, 83% of the banded adults were found on the same territory. Only 4 of 129 banded nestlings have been reencountered in the study sites.

O cerrado é a maior, mais rica e provavelmente a mais ameaçada savana tropical do mundo. No entanto, grande parte de sua área foi ocupada por empreendimentos de agropecuária, nos quais não foram respeitados princípios básicos de conservação, sendo que cada grupo ou táxon reage de forma diferente a mudanças ambientais desse tipo. As aves de rapina, como os Falconiformes e os Strigiformes, são especialmente prejudicadas, pois são considerados predadores de topo de muitas teias alimentares. Porém, para saber como essas aves são afetadas pelas mudanças ambientais causadas pela ação do homem é necessário entender quais fatores são relevantes na \"escolha\" do ambiente de determinada espécie e assim compreender a razão de uma possível seletividade de hábitat. Sendo assim, o presente estudo observou características ecológicas de duas espécies de corujas comuns e bem distribuídas no Brasil, Megascops choliba e Athene cunicularia. Dentre os objetivos estão analisar a metodologia de estudo dessas aves de rapina, com possíveis efeitos na detecção de contatos e verificar o uso de hábitat, em diferentes fisionomias de cerrado, por parte das duas espécies de corujas. O estudo foi realizado na região da Estação Ecológica de Itirapina, no interior do estado de São Paulo. Para contatar as corujas foram realizados experimentos de playback em pontos de amostragem distribuídos em quatro fisionomias (neste estudo consideradas habitats) de cerrado. A atividade vocal de M. choliba variou conforme a temperatura e a umidade relativa. Esta espécie respondeu mais ao playback em condições de temperatura e umidade relativa altas. Athene cunicularia mostrou variar sua atividade vocal conforme a fase da lua e a intensidade do vento. Indivíduos desta espécie respondem mais intensamente ao playback em noites de lua cheia e menos em noites com ventos mais fortes. As duas espécies de corujas se distribuem diferentemente entre as fisionomias de cerrado. Athene cunicularia distribui-se distintamente entre fisionomias fechadas e abertas (Hk-w = 9,976; p = 0,0188), utilizando mais frequentemente as os campos limpo e sujo. Megascops choliba também se distribui diferentemente entre as fisionomias de cerrado (Hk-w = 10,88; p = 2 0,0137), utilizando preferencialmente o campo cerrado e o cerrado s.s.. Segundo os modelos tidos como os melhores, pela seleção de modelos feita através do AIC (Aikaike\'s Information Criterion), a variável com maior poder explicativo é o número de arbóreas para as duas espécies. Megascops choliba e A. cunicularia se segregam ecologicamente, havendo partição divergente de recursos espaciais, devido a seus requisitos para nidificação e forrageamento. Ocorre sobreposição intermediária no uso do habitat entre ambas espécies (O = 0,466). Já quanto a amplitude de nicho espacial (uso de habitat) M. choliba foi generalista (Bst = 0,753) e A. cunicularia intermediária (Bst = 0,453). Sendo assim, estas espécies divergem na seleção de habitat, se distribuindo diferentemente entre as fisionomias de cerrado de acordo com o número de arbóreas. Este estudo sugere, ainda, a importância de se levar em consideração as variáveis climáticas em estudos com o uso de vocalizações de aves de rapina noturnas, servindo também de subsídio para pesquisas futuras sobre censo dessas aves. / The Cerrado biome is the largest, richest and perhaps the most threatened tropical savannah of the world. However, most part of its natural areas has been transformed on agrosystems and pastures where basic principles of conservation weren\'t respected. Each biological group or taxa are affected on different ways by this change. Birds of prey are particularly affected because of its position in trophic webs, as they are top predators. To understand how these birds are affected by change caused by human land use, it is necessary to understand which factors are important for habitat selection, and then understand the species-habitat relationship. Thus, we observed ecological aspects of two widespread and common owls on Brazil: Tropical Screech-Owls (Megascops choliba) and Burrowing Owl (Athene cunicularia). The main objectives of this study included an analysis of methodological aspects of studying these owls species through playback and observe their habitat use. The study was conducted in the Estação Ecológica de Itirapina, State of São Paulo, Brazil. For doing it, we used playback experiments to detect these owls on four different cerrado physiognomies Vocal activities of Tropical Screech-owls were more detected in conditions of higher temperature and humidity. On the other hand, the Athene cunicularia answered more to playback in lower wind speed conditions and/or at full moon nights. The Burrowing Owl explored more frequently open physiognomies of cerrado, as campo limpo and campo sujo (Hk-w = 9.976; p = 0.0188). Conversely, Megascops choliba is more often found on campo cerrado, avoiding campo limpo (Hk-w = 10.88; p = 0.0137). According to Aikaike\'s Information Criterion (AIC) selection model, the most important variable to explain the distribution of both species in cerrado is the number of trees. There was ecological segregation between Megascops choliba and A. cunicularia. The spatial niche was intermediarily segregated (Pianka´s niche overlap measure O = 0.466), according their different needs for nesting and foraging. Additionally, these owls displayed broader (M. choliba Bst = 0.753) or intermediate (A. cunicularia Bst = 0.453) spatial niche breadths. On this sense, these owls have different needs on habitat selection, and their different distributions in cerrado were related more intrinsically to the number of trees present on each physiognomy, which is related to their nesting and foraging requirements. Aditionally, this study suggests, the importance to consider the influence of weather conditions on broadcast survey techniques for nocturnal raptors, which may be considered in further studies on census of these birds.