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- Ecologia e demografia de uma população de águia de Bonelli Aquila Fasciata em meio florestalPublication . Palma, Luis; Fonseca, Luís Cancela da; Palmeirim, JorgeA presente tese tem como objecto a população de Aquila fasciata do Sudoeste Serrano português, caracterizada pela nidificação exclusivamente arborícola, encontrar-se em acentuada expansão e apresentar marcada divergência genética em relação às populações ibéricas vizinhas. Pretendeu-se contribuir para uma base científica de uma estratégia de conservação, tendo como objectivos específicos: a) conhecer a ecologia alimentar da população, b) estudar a selecção de habitat de uma presa fundamental, o coelho-bravo; c) avaliar os níveis de contaminação ambiental da população; d) desenvolver métodos expeditos de sexagem de juvenis; e) rastrear agentes infecciosos potencialmente letais e f) avaliar metodologias de análise demográfica. No respeitante à dieta da população, constatou-se um elevado consumo de presas domésticas, sobretudo pombos rurais, em especial no início da época reprodutiva. Ao longo da reprodução, o coelho-bravo, a perdiz, o gaio e outras aves selvagens adquirem progressivamente maior importância. A selecção entre pombos e coelhos é inversamente denso-dependente, sendo o pombo rural uma presa complementar aos coelhos e perdizes e não unicamente uma presa alternativa em situação de escassez destes. O estudo da selecção de habitat do coelho-bravo mostrou que prefere estevais de densidade intemédia, por fornecerem simultaneamente abrigo contra predadores e recursos alimentares nos estratos herbáceo e arbustivo. O estudo dos níveis de mercúrio na população evidenciou uma forte variação espacial, indiciando uma fonte poluidora em Sines. Desenvolveram-se dois métodos expeditos de sexagem morfométrica, validados por métodos moleculares, os quais permitem comprovar a sexagem em aves subnutridas. Esta ocorrência está associada à elevada prevalência de tricomoníase, potencialmente letal em juvenis nidícolas, devido à frequente ingestão de pombos rurais infectados. A análise dos parâmetros demográficos mostrou não ser possível inferir qualquer padrão de fecundidade denso-dependente na população estudada. Considerar apenas os dois mecanismos usualmente utilizados para explicar a fecundidade densodependente em populações naturais pode não ser o mais adequado.
- Why do raptors take domestic prey? The case of Bonelli's eagles and pigeonsPublication . Palma, Luis; Beja, Pedro; Pais, Miguel; Cancela Da Fonseca, LuísPredator conservation management requires detailed understanding of the ecological circumstances associated with predation, especially that on economically valuable prey. We examined the mechanisms behind Bonelli's eagle Hieraaetus fasciatus predation on prey of domestic origin, using dietary data from 22 pairs breeding in south-west Portugal (1992-2001) together with information on landscape composition and prey availability. 2. Numerically, 42.7% (37.7% in biomass) of eagle prey comprised domestic species, about 70% of which were rural pigeons Columba livia and the remainder were racing pigeons Columba livia and domestic fowl Gallus gallus. Rabbits Oryctolagus cuniculus, red-legged partridges Alectoris rufa and jays Garrulus glandarius were the most frequent wild prey (43.1%; 50.8% in biomass). This dietary pattern was remarkably stable over a decade, but within each year the intake of pigeons almost halved over the course of the breeding season. 3. Landscape composition significantly affected the dietary proportion of wild and domestic prey items. This was particularly evident in territories dominated by eucalyptus Eucalyptus globulus plantations, where there was reduced consumption of rural pigeons and partridges, an increased intake of minor avian prey items and greater diversity in the diet overall. 4. Bonelli's eagles showed type II functional responses while preying on the most important wild (rabbit) and domestic (rural pigeon) prey, although the former was much stronger. Eagle predation on rabbits declined with increasing abundance of pigeons, and vice versa, but there was no switching in the traditional sense, as selection between these two species was inversely frequency dependent. 5. Synthesis and applications. Predation by Bonelli's eagle on domestic pigeons results from a combination of high vulnerability of the pigeons to eagles and a shortage of key wild prey such as rabbits and partridges, especially during the early breeding season. Given the relatively low economic value of rural pigeons and their importance in the diet of Bonelli's eagles, they could probably be used as a conservation tool to enhance food resources in breeding territories and to deflect predation from more valuable prey such as partridges and racing pigeons.
- The use of sighting data to analyse Iberian lynx habitat and distributionPublication . Palma, Luis; Beja, Pedro; Rodrigues, Miguel1. Over a large part of its very restricted and fragmented range, Iberian lynx Lynx pardinus occur in remote mountainous country at low density, where the only information about the species comprises records of incidental sightings obtained by inquiry. In this study we developed an approach for quantifying lynx-habitat relationships and distribution patterns from sighting data, using records from western Algarve (Portugal) in 1990-95. 2. Habitat was described in terms of land cover, topography, human disturbance and rabbit abundance, in 25-km(2) cells surrounding lynx sightings and at random locations within the study area. 3. Lynx sightings were consistently associated with predictable habitat features. Sighting probabilities estimated from a logistic regression model increased with the abundance of rabbits and the proportion of land covered by tall Mediterranean maquis, and declined with road density and the amount of developed land. This model identified correctly 85.7% of lynx sightings; at the same time only 20.7% of the random locations were misclassified. 4. Indices of human presence were never associated positively with lynx sightings, suggesting that observation patterns were not influenced by the spatial distribution of potential observers. 5. Kriging was used to interpolate spatially between sighting probabilities derived from the logistic model in order to produce a map of sighting potential for the Iberian lynx in western Algarve. Jack-knife resampling assessed the accuracy of this map. Three well-defined areas of high sighting potential were identified, probably representing the lynx core areas in this region. 6. Our analysis of lynx sighting records suggests that these data may provide a first approximation to lynx habitat and distribution when further information is lacking. The application of this approach to other ran and reclusive species is discussed.