Jessica Cornils


PDF im Hochschulschriften-Service der Universität Wien

Population density and habitat preferences of the Black-cheeked Ant-Tanager Habia atrimaxillaris.

The Pacific tropical lowland forest in the southwestern part of Costa Rica has an extremely diverse avifauna. Our study object the Black-cheeked Ant-Tanager (Habia atrimaxillaris) is a highly range-restricted species with a remaining population in the area of Piedras Blancas and Corcovado National Park. It is assumed that the population is decreasing due to habitat loss and fragmentation. We assessed the population density of this species in the vicinity of the Tropical Research Station La Gamba using the method of distance sampling (two survey periods: February-April 2009 and November 2010 to January 2011) and territory mapping (November 2010 to January 2011). Furthermore the point count method and data on vegetation structure were used to study its habitat preferences. Therefore, 40-44 point counts were conducted per census point between 1 November 2008 and 4 October 2010 at the interior of old-growth forest (10 census points), the margin of old-growth forest (10), young secondary forests (5), gallery forest strips connected to and isolated from closed forest (both 10), oil palm plantations (5), fallows (5) and pastures (5). The species’ occurrence at old-growth forest sites was then related to forest cover (within a radius of 200 m around census points) and vegetation structure. Black-cheeked Ant-Tanagers were exclusively found in old growth forest where the species’ likelihood of occurrence at census points increased with forest cover, canopy cover and density of trees (with diameter at breast height >10 cm). An average population density between 24 and 27 individuals per km² was estimated by distance sampling, which is in accordance with the population size estimated by territory mapping (17-25 birds per km²). Based on these estimates an overall population size of 12,432 to 20,720 birds is predicted for the remaining 592 km² lowland forest area of the Golfo Dulce region. Since the Black-cheeked Ant-Tanager was only recorded in old-growth forest, apparently does not use strips of gallery forests embedded in a human-dominated landscape matrix as stepping stones or corridors and appears to avoid the forest edge, further forest degradation and fragmentation will have a strong negative impact and should be rapidly reduced by adequate conservation measures.