Examination of parental investment in nest defence in a tropical songbird, the Pied Bush Chat (Saxicola caprata)

Most animals that demonstrate parental care are also engaged in such behaviour that increases their offspring chance of survival when confronted by a predator. The present study is equipped with a detailed account of the parental investment in nest defence behaviour of a tropic zone (Haridwar, Himalayan foothills, India) inhabiting species, the Pied Bush Chat (Saxicola caprata) (PBC). During simulated nest defence treatments, we recorded two distinct types of calls which were used during the display of parental aggression by PBCs, threat calls and alarm calls. Significant differences were noted for the usage of the threat calls over the alarm calls during nest defence. For the most part males were found to be more aggressive than females (on the basis of their call rates) during the simulated attacks of the decoy predator. Results also indicated that parental aggression was more inclined towards nestlings than that of the eggs. The results were consistent with the hypothesis that the nest protection intensity increases with the progression of the nesting cycle.