A comparison of nest-site characteristics for two sympatric Estrildid finches ( Uraeginthus spp.) in Tanzania.

It is well known that birds have great diversity in nesting strategies, but we still have limited knowledge of the variation among species that share the habitat. Here, I will report and compare the nesting strategies between the two sympatric songbirds. Blue-capped ( Uraeginthus cyanocephalus ) and red-cheeked cordon-bleus ( Uraeginthus bengalus ) are socially monogamous, biparental songbirds (family Estrildidae) that sympatrically inhabit arid landscapes with trees and bushes in East Africa. Both species build domed nests with grasses that are often located near wasp nests. They also sometimes take over old weaver (family Ploceidae) nests. While these nesting strategies are already described as common behavioral traits in both species in the literature, interspecies variation in these nesting strategies in areas of sympatry is not reported. My initial field observation during their breeding season suggested that whether these nesting strategies were adopted or not varied somewhat between the sympatric cordon-bleus. Thus, I carried out a more formal investigation to test these differences. I found that red-cheeked cordon-bleus built their nests near wasp nests more frequently than blue-capped cordon-bleus, while I did not find any other significant differences between the nesting sites of the two species, such as the use of weaver nests, the types of nesting plants, or nest heights. These results suggest that the sympatric cordon-bleus share several nest-site characteristics, but that red-cheeked cordon-bleus have an affinity for nesting near wasp nests. Further studies will be required to elucidate the costs and benefits of these nesting strategies or the role that adjacency to wasp nests might play in the sympatry of the two species.