61 research outputs found
Assessment of the distribution of two sympatric rail species in relation to habitat composition and disturbance on Santa Cruz Island, Galápagos
No full textThe Galápagos archipelago is a biodiversity hotspot with relatively few extinctions recorded. However, a negative trend for Galápagos rail’s population in Santa Cruz Island was confirmed. We aim to evaluate the species’ population status, assess the role of habitat composition on its distribution and describe the first insights about which factors affects its distribution and the paint-billed crake’s distribution. Point counts with fixed distance were used in four areas to census both species, using 197 points from 2007 and an additional 111 points. We also assessed the vegetation cover in the tree, shrub, and ground layers. The Galápagos rail detection and abundance significantly increased in Highlands Media Luna since 2007 due to a significant decrease in the occurrence of the red-barked quinine tree. However, the hill blackberry had significantly increased. The Galápagos rail seems to be related with dense ground vegetation. Its population is at the same levels as in 1986, but there is little evidence of about the factors influencing the distribution of both species, based only on habitat requirements; Avaliação da distribuição de Laterallus spilonota em relação ao habitat e a Mustelirallus erythrops, na ilha de Santa Cruz, Galápagos - Resumo:
As ilhas Galápagos são consideradas um “hotspot” de biodiversidade onde ocorreram poucas extinções, apesar da população de Laterallus spilonota ter reduzido acentuadamente em Santa Cruz. Os nossos objetivos são avaliar o status da sua população e o papel que a composição do habitat tem na sua distribuição, bem como apresentar as primeiras evidências sobre quais os fatores que afetam a distribuição de L. spilonota e Mustelirallus erythrops. Para realizar os censos de ambas as espécies foram utilizados pontos com distância fixa em 4 áreas de Santa Cruz. Foram usados os mesmos 197 pontos de 2007 e 111 pontos adicionais. Foi também avaliada a cobertura vegetal no estrato arbóreo, arbustivo e herbáceo. A deteção e abundância de L. spilonota aumentaram significativamente em Highlands Media Luna desde 2007, devido a uma diminuição significativa da ocorrência de Cinchona pubescens. Porém, a ocorrência de Rubus niveus aumentou significativamente. Laterallus spilonota parece ser mais abundante em locais onde a vegetação herbácea é densa, estando a sua população nos mesmos níveis de 1986. Além disso, existem poucos indícios sobre a distribuição das duas espécies apenas com base na composição do habitat; Evaluación de la distribución del Pachay en relación con el hábitat y la Gallareta de Pico Rojo, en la isla Santa Cruz, Galápagos - Resumen:
Las islas Galápagos son un “hotspot” de biodiversidad con pocos registros de extinciones, aunque la población del pachay se ha reducido notablemente en Santa Cruz. Nuestros objetivos son evaluar el estado de su población y el papel que la composición del hábitat tien en su distribución, así como presentar las primeras pruebas sobre qué factores afectan a la distribución del pachay e de la gallareta de pico rojo. Para realizar los censos de ambas especies se utilizaron puntos con distancia fija en 4 zonas de Santa Cruz. Se utilizaron los mismos 197 puntos de 2007 y 111 puntos adicionales. También se evaluó la cobertura vegetal en el estrato arbóreo, arbustivo y herbáceo. La detección y la abundancia del pachay aumentaron significativamente en Media Luna desde 2007, debido a una disminución significativa de la presencia de cascarilla. Sin embargo, la presencia de mora aumentó significativamente. El pachay parece ser más abundante en los lugares donde la vegetación herbácea es densa y su población se encuentra en los mismos niveles que en 1986. Además, hay pocas pruebas sobre la distribución de las dos especies basándose únicamente en la composición del hábitat
Philornis downsi - a recently discovered parasite on the Galápagos archipelago - a threat for Darwin's finches?
No full textThe obligate dipterian bird parasite Philornis downsi and the facultative parasitic fly Sarcodexia lambens were, until recently, unknown on the Galapagos archipelago. The first sign of parasitism of P. downsi on Darwin's finches was found in 1997. Parasitism data were collected from 177 nests of 12 bird species, including eight endemic species. In this study we examined host specificity, infection prevalence (percentage of infested nests), parasite load per nest and per nestling, and breeding success for two climatically different years, 1998 and 2000. We found Philornis downsi in 97% of the investigated nests, Sarcodexia lambens in 32% of the nests and a still unidentified endoparasitic Muscidae in 87% of the clutches investigated. The first two ectoparasites showed no host preference and were found in the dry deciduous coastal zone as well as in the evergreen moist forest. Parasite load per nest varied through the breeding stages, with no parasites during incubation, but with numbers increasing with nestling development. Parasite load per nest showed little variation, but variation in brood size led to different infestation rates per nestling. Small broods suffered higher parasite loads and higher nestling mortality, thus inducing a possible impact on population dynamics.</p
Interannual and interspecific variation in intensity of the parasitic fly, Philornis downsi, in Darwin's finches
No full textExploration and ecology in Darwin’s finches
No full textOne of the main functions of exploratory behaviour is to gain information about the environment. The adaptive value of such behaviour should vary with ecological conditions influencing the diversity and stability of resources, as well as with the costs associated with gathering information. Consequently, predictions can be made about environmental factors influencing the evolution of exploration. We used comparative methods, combining a field experiment with literature data, to study correlated evolution between explorative behaviour and ecology among 13 species of Darwin’s finches. Controlling for phylogenetic influences, we found that exploration (measured as the proportion of individuals responding in the experiment) increased with diet diversity and the amount of fruit in diet, consistent with theories stating that exploration aimed at finding new food types should be more beneficial for generalists than for specialists. However, our study is the first to demonstrate a correlation between neophilia and food diversity. Contrary to our prediction, species with a high percentage of concealed food in their diet were less explorative. A possible explanation for this novel finding is that in our study system concealed food may be a stable resource, and species using such resources should be less dependent on the discovery of new food types
Avian nest defence behaviour: assessment in relation to predator distance and type, and nest height
No full textEffects of the introduced ectoparasite Philornis downsi on haemoglobin level and nestling survival in Darwin's Small Ground Finch (Geospiza fuliginosa)
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No full textInsects, mammals and birds are known to use tools, but empirical evidence of the ecological importance of tool-use is scarce. Here, we present the first ecological study of tool-use by a bird species. Woodpecker finches use twigs or cactus spines to pry arthropods out of tree-holes. We compared tool-use during wet and dry seasons in two different vegetation zones: the Arid Zone and the humid Scalesia Zone. In the Scalesia Zone, where food was abundant and easily accessible, woodpecker finches rarely used tools. In contrast, in the Arid Zone, where food was limited and hard to access, they obtained half of their prey using tools during the dry season. Tool-use enabled the birds to reach particularly large and otherwise inaccessible prey hidden in tree-holes. Our data suggest that tool-use in the woodpecker finch has evolved in response to the dry and unpredictable conditions in the coastal zone of the Galapagos Islands.</p
Evolutionary dead end in the Galápagos: divergence of sexual signals in the rarest of Darwin's finches.
No full textUnderstanding the mechanisms underlying speciation remains a challenge in evolutionary biology. The adaptive radiation of Darwin's finches is a prime example of species formation, and their study has revealed many important insights into evolutionary processes. Here, we report striking differences in mating signals (songs), morphology and genetics between the two remnant populations of Darwin's mangrove finch Camarhynchus heliobates, one of the rarest species in the world. We also show that territorial males exhibited strong discrimination of sexual signals by locality: in response to foreign songs, males responded weaker than to songs from their own population. Female responses were infrequent and weak but gave approximately similar results. Our findings not only suggest speciation in the mangrove finch, thereby providing strong support for the central role of sexual signals during speciation, but they have also implications for the conservation of this iconic bird. If speciation is complete, the eastern species will face imminent extinction, because it has a population size of only 5-10 individuals
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