Structure, density and rarity in an Amazonian rainforest bird community

Abstract

ABSTRACT A 100-ha quadrat of primary rainforest in French Guiana was ccnsused over two consecutive years by the mapping method, and a 24-ha core area was intensively mistnetted at the same time. More extensive surveys were conducted in successively larger areas including up to a large part of the forested interior of the country. From a total of 441 resident species found in the rainforest zone, 248 were regularly recorded within the 100-ha plot, 157 of which had mean densities of more than 1 pair km -2 . The total estimated density of birds was at least 829 pairs km -2 . Only two dominant species exceeded 20 pairs km -2 , while 52% of all the species were represented by less than 2 pairs km -2 . The distribution of body masses and niche characteristics among the bird community is given as well as the sample bias of the mistnet captures. Rare species were a key component of this primary rainforest community. Several patterns of rarity were described and no marked and constant relationships were found between rarity and body size, habitat, diet, foraging behaviour or social system. Among a wide set of environmental constraints, the population of each species may be limited by a different combination of factors. Habitat heterogeneity, low, irregular and seasonal food availability, interspecific competition or heavy predation pressure were prominent and likely causes of the low density of most species which in turn facilitated the high species richness.