As escolhas de um predador podem variar de acordo com a abundância da presa no ambiente, atributos físicos e comportamentais da presa e do predador, além do custo energético, resultando na seleção de determinadas presas em detrimento de outras. Os raros estudos de seletividade na dieta da coruja-buraqueira (Athene cunicularia) realizados no Brasil tiveram como foco a seleção de roedores. Por este motivo o presente estudo tem como objetivos, além do estudo quantitativo da dieta, verificar se ocorre seletividade de coleópteros copro-necrófagos por A. cunicularia e se atributos da presa e/ou do predador, além de parâmetros climáticos, podem influenciar na predação e seletividade. Foram utilizados restos de presas (ossos, mandíbulas, cinturas pélvicas, élitros, pronotos e cabeças) encontrados nas pelotas e ao redor dos ninhos nos campos do Cerrado da Estação Ecológica de Itirapina (São Paulo) para identificação das espécies, quantificação do número de indivíduos consumidos e biomassa bruta ingerida. A sazonalidade na dieta foi testada por meio do teste-G de independência (tabela de contingência). Foram calculados os índices de amplitude de nicho trófico de Levins (Bst) para cada coleta, e efetuado o teste de Mann-Whitney para avaliar sazonalidade na amplitude da dieta entre a estação chuvosa e seca. Dados climáticos como temperatura máxima e média, umidade e pluviosidade médias foram relacionados com os números de indivíduos dos grupos predominantes na dieta e no campo por meio da correlação de Pearson. A análise da seleção de besouros escarabeíneos (copro-necrófagos) foi realizada por meio do intervalo de confiança de Bailey. Foram coletadas 421 pelotas e 183 debris que resultaram em 4341 presas individuais e uma biomassa total de 6.184,75 g. A dieta da A. cunicularia numericamente é predominantemente composta por insetos (92,88%), principalmente Coleoptera (48,4%), Orthoptera (10,1%) e Blattaria (16,7%). As famílias mais frequentes de coleópteros foram Scarabaeidae (26,2%) e Carabidae (8,7%). Por outro lado, em termos de biomassa bruta ingerida, os vertebrados foram importantes com 40,20%. Não houve diferenças sazonais na amplitude de nicho trófico (U = 11; p = 0,153), porém ao se considerar as frequências absolutas (número de indivíduos) houve significantemente, maior consumo de insetos (principalmente besouros escarabeídeos) e anuros na estação chuvosa e de roedores na estação seca (G independência = 644,9; g.l. = 11; p < 0,0001). Em alguns casos, a predação e a abundância das presas foram positivas e diretamente relacionadas com a temperatura, umidade e precipitação. Os escarabeíneos foram mais coletados e consumidos com o aumento da temperatura, umidade e pluviosidade médias. A amplitude da dieta para A. cunicularia na EEI foi considerada ampla, apesar dos valores de Bst próximos à zero. As corujas estudadas selecionaram alguns coleópteros copro-necrófagos (Scarabaeidae: Scarabaeinae) encontrados na EEI, selecionando três espécies do gênero Dichotomius (sp. 1, sp. 2 e sp. 3) na estação chuvosa e Dichotomius glaucus, (sp. 1 e sp. 3) e Coprophanaeus ensifer na seca. Estes escarabeídeos podem ser vulneráveis a predação por causa de aspectos de sua biologia, como hábito terrícola, atividade nas horas crepusculares-noturnas, movimento lento, falta de defesa ativa, e tamanho adequado (15-25 mm; 0.8-2.0 g) ao consumo para o porte da coruja-buraqueira. / Predator\'s choice can change according to prey abundance in the environment, physical and behavioral traits both of predator and prey, and energy cost whose influences may result in selection of some prey. The rare prey selection studies of the Burrowing-Owl in Brazil were focused only in small mammals. The aims of this research were to study quantitatively the diet of the Burrowing-Owl and to analyze dung beetle prey selection, searching if any prey and/or predator traits, as well as if climatic parameters may influence on selectivity and predation. Prey remains (bones, mandibles, pelvic girdles, elytron, and heads) found in pellets and in the nest sites at the grasslands of Ecological Station of Itirapina (State of São Paulo, southeast Brazil) were utilized to identify prey species, to quantify number of consumed individuals and ingested biomass. The seasonality in the diet was evaluated by G-test (table of contingency). The index of food niche breadth (Bst) was calculated for each month and its seasonality between rainy and dry season was evaluated by Mann-Whitney\'U-test. Weather variables such as mean figures of maximum and mean temperature, mean precipitation and air relative humidity were analyzed to reveal possible correlations with number of prey items collected in pellets and in the environment. For this analysis the Pearson\'s correlation (r) was calculated. The analysis of dung bettles selection was conducted by Bailey\'s confidence intervals. A total of 421 pellets and 183 debris were collected yielding 4341 prey individuals and 6,184.75 g of estimated biomass. Insects were the most frequent prey in the Burrowing-Owl\'s diet (92.88%), mainly Coleoptera (48.4%), Orthoptera (10.1%) and Blattaria (16.7%). The most frequent beetle families were Scarabaeidae (26.2%) and Carabidae (8.7%). On the other hand, vertebrates were important in terms of biomass (40.20%). There was no seasonality on the food-niche breadth (U = 11, p = 0.153), but by absolute frequencies (number of prey) there was a significantly higher consumption of insects (mainly scarabs) and frogs in the wet season, and rodents in the dry season (G = 644.9; d.f. = 11; p < 0.0001). In some instances predation and abundance of prey had positive and directly proportional correlation with temperature, humidity and rainfall. The dung beetles were more consumed and available in the environment with increasing temperature, humidity and rainfall averages. The food-niche breadth was wide despite of the Bst values near zero. The Burrowing-owl selected some dung beetles (Scarabaeidae: Scarabaeinae) these being Dichotomius (sp. 1, sp. 2 and sp. 3) at rainy and Dichotomius glaucus, (sp. 1 e sp. 3) and Coprophanaeus ensifer at the dry season. These scarabs may be vulnerable because some of its biological traits. Dichotomius are ground medium beetles which forage at twilight/night, and has an adequate size (15-25 mm; 0.8-2.0 g) for the Burrowing-Owl size.

As escolhas de um predador podem variar de acordo com a abundância da presa no ambiente, atributos físicos e comportamentais da presa e do predador, além do custo energético, resultando na seleção de determinadas presas em detrimento de outras. Os raros estudos de seletividade na dieta da coruja-buraqueira (Athene cunicularia) realizados no Brasil tiveram como foco a seleção de roedores. Por este motivo o presente estudo tem como objetivos, além do estudo quantitativo da dieta, verificar se ocorre seletividade de coleópteros copro-necrófagos por A. cunicularia e se atributos da presa e/ou do predador, além de parâmetros climáticos, podem influenciar na predação e seletividade. Foram utilizados restos de presas (ossos, mandíbulas, cinturas pélvicas, élitros, pronotos e cabeças) encontrados nas pelotas e ao redor dos ninhos nos campos do Cerrado da Estação Ecológica de Itirapina (São Paulo) para identificação das espécies, quantificação do número de indivíduos consumidos e biomassa bruta ingerida. A sazonalidade na dieta foi testada por meio do teste-G de independência (tabela de contingência). Foram calculados os índices de amplitude de nicho trófico de Levins (Bst) para cada coleta, e efetuado o teste de Mann-Whitney para avaliar sazonalidade na amplitude da dieta entre a estação chuvosa e seca. Dados climáticos como temperatura máxima e média, umidade e pluviosidade médias foram relacionados com os números de indivíduos dos grupos predominantes na dieta e no campo por meio da correlação de Pearson. A análise da seleção de besouros escarabeíneos (copro-necrófagos) foi realizada por meio do intervalo de confiança de Bailey. Foram coletadas 421 pelotas e 183 debris que resultaram em 4341 presas individuais e uma biomassa total de 6.184,75 g. A dieta da A. cunicularia numericamente é predominantemente composta por insetos (92,88%), principalmente Coleoptera (48,4%), Orthoptera (10,1%) e Blattaria (16,7%). As famílias mais frequentes de coleópteros foram Scarabaeidae (26,2%) e Carabidae (8,7%). Por outro lado, em termos de biomassa bruta ingerida, os vertebrados foram importantes com 40,20%. Não houve diferenças sazonais na amplitude de nicho trófico (U = 11; p = 0,153), porém ao se considerar as frequências absolutas (número de indivíduos) houve significantemente, maior consumo de insetos (principalmente besouros escarabeídeos) e anuros na estação chuvosa e de roedores na estação seca (G independência = 644,9; g.l. = 11; p < 0,0001). Em alguns casos, a predação e a abundância das presas foram positivas e diretamente relacionadas com a temperatura, umidade e precipitação. Os escarabeíneos foram mais coletados e consumidos com o aumento da temperatura, umidade e pluviosidade médias. A amplitude da dieta para A. cunicularia na EEI foi considerada ampla, apesar dos valores de Bst próximos à zero. As corujas estudadas selecionaram alguns coleópteros copro-necrófagos (Scarabaeidae: Scarabaeinae) encontrados na EEI, selecionando três espécies do gênero Dichotomius (sp. 1, sp. 2 e sp. 3) na estação chuvosa e Dichotomius glaucus, (sp. 1 e sp. 3) e Coprophanaeus ensifer na seca. Estes escarabeídeos podem ser vulneráveis a predação por causa de aspectos de sua biologia, como hábito terrícola, atividade nas horas crepusculares-noturnas, movimento lento, falta de defesa ativa, e tamanho adequado (15-25 mm; 0.8-2.0 g) ao consumo para o porte da coruja-buraqueira. / Predator\'s choice can change according to prey abundance in the environment, physical and behavioral traits both of predator and prey, and energy cost whose influences may result in selection of some prey. The rare prey selection studies of the Burrowing-Owl in Brazil were focused only in small mammals. The aims of this research were to study quantitatively the diet of the Burrowing-Owl and to analyze dung beetle prey selection, searching if any prey and/or predator traits, as well as if climatic parameters may influence on selectivity and predation. Prey remains (bones, mandibles, pelvic girdles, elytron, and heads) found in pellets and in the nest sites at the grasslands of Ecological Station of Itirapina (State of São Paulo, southeast Brazil) were utilized to identify prey species, to quantify number of consumed individuals and ingested biomass. The seasonality in the diet was evaluated by G-test (table of contingency). The index of food niche breadth (Bst) was calculated for each month and its seasonality between rainy and dry season was evaluated by Mann-Whitney\'U-test. Weather variables such as mean figures of maximum and mean temperature, mean precipitation and air relative humidity were analyzed to reveal possible correlations with number of prey items collected in pellets and in the environment. For this analysis the Pearson\'s correlation (r) was calculated. The analysis of dung bettles selection was conducted by Bailey\'s confidence intervals. A total of 421 pellets and 183 debris were collected yielding 4341 prey individuals and 6,184.75 g of estimated biomass. Insects were the most frequent prey in the Burrowing-Owl\'s diet (92.88%), mainly Coleoptera (48.4%), Orthoptera (10.1%) and Blattaria (16.7%). The most frequent beetle families were Scarabaeidae (26.2%) and Carabidae (8.7%). On the other hand, vertebrates were important in terms of biomass (40.20%). There was no seasonality on the food-niche breadth (U = 11, p = 0.153), but by absolute frequencies (number of prey) there was a significantly higher consumption of insects (mainly scarabs) and frogs in the wet season, and rodents in the dry season (G = 644.9; d.f. = 11; p < 0.0001). In some instances predation and abundance of prey had positive and directly proportional correlation with temperature, humidity and rainfall. The dung beetles were more consumed and available in the environment with increasing temperature, humidity and rainfall averages. The food-niche breadth was wide despite of the Bst values near zero. The Burrowing-owl selected some dung beetles (Scarabaeidae: Scarabaeinae) these being Dichotomius (sp. 1, sp. 2 and sp. 3) at rainy and Dichotomius glaucus, (sp. 1 e sp. 3) and Coprophanaeus ensifer at the dry season. These scarabs may be vulnerable because some of its biological traits. Dichotomius are ground medium beetles which forage at twilight/night, and has an adequate size (15-25 mm; 0.8-2.0 g) for the Burrowing-Owl size.

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.

Made available in DSpace on 2014-06-11T19:30:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-06-14Bitstream added on 2014-06-13T19:00:00Z : No. of bitstreams: 1 zilio_f_me_rcla.pdf: 677952 bytes, checksum: 730aacd8d898fa3703faa38025012043 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Duas espécies só podem coexistir durante um longo período de tempo se diferirem em alguns aspectos ecológicos. Essas são premissas do conceito de nicho ecológico de uma espécie. Falco sparverius e Athene cunicularia são aves de rapina de ocorrência comum na maioria da região neotropical. Usualmente encontradas em simpatria, ocorrem em ambientes abertos, com pouca vegetação e apresentam uma dieta similar, baseada em insetos, e comportamentos de caça semelhantes. Os ambientes costeiros do Rio Grande do Sul são sistemas frágeis, protegidos pela legislação nacional e pouco estudados. Os objetivos deste estudo são analisar como estas espécies segregam ecologicamente no ambiente em questão, avaliando as dimensões trófica, espacial e temporal de nicho. Adicionalmente, objetiva-se contribuir para o conhecimento da ecologia destas espécies. Entre março/2000 e janeiro/2004 foram realizadas 31 excursões mensais à área de estudo quando se coletaram pelotas de regurgitação e restos de presas. Realizaram-se ainda observações de captura de presas, análise de comportamento circadiano e uso de hábitat de F. sparverius e A. cunicularia. Corroborando outros estudos, ambas espécies mostraram-se predadores generalistas e oportunistas, consumindo predominantemente invertebrados, com baixo consumo de vertebrados, havendo, aparentemente, variação sazonal na dieta. / Two species can coexist during a long time period only if both differ in some ecological aspect. This is a premise of the ecological niche theory. Falco sparverius and Athene cunicularia are two most common raptors in the neotropical region. Usually sympatric, these species inhabit open countries, with few vegetation and have similar diets, including mainly insects, and similar foraging behaviors. The coastal habitats of Rio Grande do Sul are fragile and poorly studied ecosystems under Brazilian legislation protection. This study aims to analyze how these species segregate themselves in coastal habitats by investigating the trophic, spatial and temporal niche dimensions. Additionally, it is our intention to contribute to knowledge of the ecology of these species. Between March/2000 and January/2004, 31 monthly field expeditions were conducted to the study area during which pellets and prey remains were collected. Further, captures attempts were recorded and daily behavior and foraging habitat use of the F. sparverius and A. cunicularia were analyzed. Corroborating previous studies, both species showed to be generalist and opportunist predators, eating mainly invertebrates, with little vertebrate consumption, having, apparently, seasonal variation in their diet.

Orientador: Marco Aurélio Pizo Ferreira / Banca: José Carlos Motta Júnior / Banca: Roberto Goitein / Resumo: Duas espécies só podem coexistir durante um longo período de tempo se diferirem em alguns aspectos ecológicos. Essas são premissas do conceito de nicho ecológico de uma espécie. Falco sparverius e Athene cunicularia são aves de rapina de ocorrência comum na maioria da região neotropical. Usualmente encontradas em simpatria, ocorrem em ambientes abertos, com pouca vegetação e apresentam uma dieta similar, baseada em insetos, e comportamentos de caça semelhantes. Os ambientes costeiros do Rio Grande do Sul são sistemas frágeis, protegidos pela legislação nacional e pouco estudados. Os objetivos deste estudo são analisar como estas espécies segregam ecologicamente no ambiente em questão, avaliando as dimensões trófica, espacial e temporal de nicho. Adicionalmente, objetiva-se contribuir para o conhecimento da ecologia destas espécies. Entre março/2000 e janeiro/2004 foram realizadas 31 excursões mensais à área de estudo quando se coletaram pelotas de regurgitação e restos de presas. Realizaram-se ainda observações de captura de presas, análise de comportamento circadiano e uso de hábitat de F. sparverius e A. cunicularia. Corroborando outros estudos, ambas espécies mostraram-se predadores generalistas e oportunistas, consumindo predominantemente invertebrados, com baixo consumo de vertebrados, havendo, aparentemente, variação sazonal na dieta / Abstract: Two species can coexist during a long time period only if both differ in some ecological aspect. This is a premise of the ecological niche theory. Falco sparverius and Athene cunicularia are two most common raptors in the neotropical region. Usually sympatric, these species inhabit open countries, with few vegetation and have similar diets, including mainly insects, and similar foraging behaviors. The coastal habitats of Rio Grande do Sul are fragile and poorly studied ecosystems under Brazilian legislation protection. This study aims to analyze how these species segregate themselves in coastal habitats by investigating the trophic, spatial and temporal niche dimensions. Additionally, it is our intention to contribute to knowledge of the ecology of these species. Between March/2000 and January/2004, 31 monthly field expeditions were conducted to the study area during which pellets and prey remains were collected. Further, captures attempts were recorded and daily behavior and foraging habitat use of the F. sparverius and A. cunicularia were analyzed. Corroborating previous studies, both species showed to be generalist and opportunist predators, eating mainly invertebrates, with little vertebrate consumption, having, apparently, seasonal variation in their diet / Mestre

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.

The first observations of Florida burrowing owls (Athene cunicularia floridana) occurred in the 19th century on historical dry prairie habitat in south central Florida. These early observations documented the ecology of burrowing owls in rural environments. Since then the vast majority of research on this subspecies has been undertaken in suburban and urban environments during the breeding period. The research undertaken on burrowing owls in suburban and urban environments includes determining natal dispersal distance, assessing female fecundity, mate fidelity, territory fidelity, date of juvenile and adult dispersal from breeding habitat, date of clutch initiation, nesting success, density of breeding pairs, causes of mortality, prey preference, and minimum annual survival of fledglings, juveniles, and adults. Very little research has been undertaken on burrowing owls in rural environments. The purpose of this thesis was to elucidate the behavior and ecology of burrowing owls in a rural environment. The topics researched in this thesis include home range in breeding habitat, dispersal distance to post-breeding habitat, location of post-breeding habitat, behavior during the breeding period, diet of rural versus urban owls, and the evaluation of three methods to trap burrowing owls. The results of this thesis indicate that, during the daytime, juvenile burrowing owls utilized habitat very close to the main and satellite burrows during the breeding period. At night juvenile owls foraged in an extensive saw palmetto patch surrounding the breeding habitat. The predominant prey of both rural and urban burrowing owls during the breeding period was insects. Dispersal of juvenile burrowing owls from breeding habitat coincided with the flooding of the breeding habitat during the rainy season.

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.

The full geographic distribution and habitat use of the Florida Burrowing Owl, a state "Species of Special Concern," is not well-understood, particularly in remote, non-urban areas. This thesis aimed to expand and improve knowledge about non-urban burrowing owls. We first compiled databases of historic sighting observations. Fieldwork verified and updated existing breeding observation point records and also yielded new breeding locations. Using a GIS, we characterized observed land use, landcover, relevant soil attributes, projected future land use and managed area status for selected points. We quantified landcover within biologically-determined buffer distances around burrows from our own field-verified records. Using standard resource selection methods, we compared observed and available proportions, calculated selection indices, and determined selection/avoidance for each landcover class. These empirical results were used in combination with expert opinion and literature review to finalize criteria for and map "suitable" landcover. Suitability of relevant soil attributes were also empirically-determined and used to further reduce the overall "suitable" area. The final suitable habitat maps appear to relate well to the overall distribution of known non-urban burrowing owl records and demonstrate that a great deal of potentially-suitable breeding habitat exists throughout Florida's central interior. Improved pasture, the most prevalent landcover class, also appears to be the most strongly selected in this study and may be of high importance to non-urban, breeding burrowing owls. Our results could be useful to wildlife officials managing this species. Recommendations include improving surveys and conservation efforts in non-urban areas and enhancing cooperation with landowners, particularly ranchers, as success on private lands seems critical to the long-term persistence of this species.