Compensation strategy: avian cup shaped nests are more exposed but better concealed than dome shaped nests

Abstract

Dome shaped nests in birds is assumed to have evolved as a strategy to reduce predation pressure on offspring. Hence, this study postulates that bird species which lack the skill to weave such nests should adopt other strategies to conceal their young from predators as they are under more selective pressure due to the exposed nature of their nests. Thus, if this hypothesis is true, it was expected that species building such nests would place them at such sites having more dense vegetation cover as compared to species with dome shaped nests. Thus, using quadrates placed around each nests found in the study, the following vegetation variables were estimated at each nest site; shrub cover, grass cover, tree cover and bare ground. In addition, attributes of nest location on substrate such as distance of nest from ground level, distance from canopy top and to the edge of the canopy were also quantified. Cup shaped nests were observed to be placed more significantly around areas with high shrub cover, grass cover and areas with less bare ground suggestive of a strategy by birds building such nests to compensate for their exposed nature by concealing them around dense vegetation areas.