Frequency and Timing of Successive Broods in Captive African and European Stonechats Saxicola torquata axillaris and S. t. rubicola

Abstract

African Stonechats at the equator in Kenya breed only once per season, whereas European Stonechats breed two or three times. To learn whether this difference in annual brood number results mainly from the differences in environmental conditions in the field or is endogenously determined, pairs of both subspecies were kept in controlled conditions and their behaviour was monitored. In the laboratory the difference between the subspecies found in the field was no longer observed: both the European and the African Stonechats were multi-brooded. In both subspecies the second or third clutches were laid while the preceding brood was still being raised (telescoping). However, the inter-brood intervals were longer for African than for European pairs. A possible functional implication of this difference is discussed. The finding that African Stonechats are just as capable as those of the European subspecies of producing multiple broods suggests that brood number in the field is limited by particular environmental factors. Canditates considered include limitation of a favourable food supply to the rainy season and the timing of the latter with respect to the endogenous breeding window. Field observations suggest that in certain exceptional conditions African Stonechats might be able to produce two broods.