Alteration of the clutch size of raptors in response to a change in prey availability: evidence from control of a broad-scale rabbit infestation.

Abstract

The claim that the clutch size of three species of raptor-the wedge-tailed eagle (Aquila audax), little eagle (Hieraaetus morphnoides) and brown goshawk (Accipiter fasciatus)-increased following the introduction and spread of the rabbit (Oryctolagus cuniculus) in Western Australia was tested by comparing historical data contained in oological collections for all 24 Australian diurnal raptors and eight owls over three time-periods: before introduction of the rabbit, during the heyday of the rabbit, and after successful broad-scale control. No significant changes were found in clutch size of the little eagle either in Western Australia or more-southerly Australia in general. Clutch size of the wedge-tailed eagle, brown goshawk and whistling kite (Haliastur sphenurus) decreased significantly after rabbit control. Clutches of two eggs were more common for the wedge-tailed eagle and those of three and four eggs were more prevalent for the brown goshawk when rabbits were uncontrolled than when controlled. These changes were not due to a shift in laying date, suggesting instead an adaptive response to changes in food availability.