Flora Bittermann



PDF im Hochschulschriften-Service der Universit├Ąt Wien

Habitat use and niche separation in Kingfisher species in the Pacific lowlands of Costa Rica.

Four kingfisher species can be observed throughout the year along rivers in the southern Pacific lowlands of Costa Rica. These closely related species forage mainly on fish but also on other aquatic organisms. Because of their similar prey and foraging behavior we expected to find at least weak evidence for niche separation, in order to avoid interspecific competition. From May to July 2010 a total of 33 stream kilometers in vicinity of the Tropical Research Station La Gamba were surveyed for kingfishers.
For each individual we recorded its sex, age and its exact geographical position. Furthermore, we measured or estimated various parameters of perching sites. Additionally a variety of habitat parameters were measured along surveyed streams on two different spatial scales, 100 m und 400 m river sections. Because the American Pygmy Kingfisher was only seen once, it was excluded from all data analyses. The remaining three species differed significantly in density (birds/stream km) and size of territories. The smallest species, the Green Kingfisher, was most abundant and occupied the smallest territories, whereas the largest Ringed Kingfisher had the lowest density and the largest territories. The three species also differed significantly in perch height. The largest species (Ringed Kingfisher) preferred higher perches than the two smaller co-occurring species, Amazon and Green Kingfisher.
Due to multicollinearity of habitat parameters a principal component analysis was calculated. The five best principal components were tested for effects on kingfisher occurrence on the two different spatial scales using generalized linear models. We only found weak evidence that the quantified habitat variables differentially affected the occurrence of the three kingfisher species along streams and rivers. Our study confirms the theory that the density of predators is negatively correlated with body size. The largest kingfisher, certainly depending on bigger prey, occupied larger territories and therefore had a lower density, than the smaller species. Otherwise, besides different perch height preferences, our data does not indicate prominent niche segregation in the three studied kingfisher species, at least during the non-breeding season.