Methods for ageing juvenile Red-billed Queleas, Queleo queleo, and their potential for the detection of juvenile dispersal patterns

Abstract

This paper evaluates potential methods for estimating the hatching dates of free-flying juvenile Red-billed Queleas, Quelea quelea, and hence establishing their likely geographical origins and patterns of post-natal dispersal. Based on studies of captive juveniles, the progress of the post-juvenile moult can discriminate up to three differently aged cohorts of young in the same population. Bill colour can help to differentiate very young birds from older ones before post-juvenile moult begins. Skull pneumatization is not useful for precise ageing; it proceeds significantly more slowly in moles than females and may not be complete by one year of age. Iris colour remains to be properly evaluated as an ageing criterion. Collections from the Okavango region of northwestern Botswana indicated that juvenile Red-billed Queleas started to arrive there as the local breeding season began. Such birds could only have originated outside Botswana in colonies established in regions of earlier rainfall, probably in those areas of South Africa or Mozambique that form the birds' 'early-rains quarters'. By the beginning of the dry season three months later, the juvenile population of northwestern Botswana comprised up to 40% of such young born elsewhere, indicating widespread long-distance natal dispersal across southern Africa.