A male-biased sex-ratio in non-breeding Hooded Plovers on a salt-lake in Western Australia

The Hooded Plover Thinornis rubricollis is a threatened, sexually monomorphic wading bird that occurs in two allopatric populations in eastern and western Australia. We used a PCR-based molecular sexing technique to sex captured birds from both populations. We found 69% of adults captured at a salt-lake in Western Australia were male. We tested for a sex-bias in our trapping technique by examining the sex-ratio of eastern birds captured under circumstances analogous to the western capture operation. No sex-bias in the trapping technique was apparent although the sample size was low. This suggests that the male-bias at the lake was real. Any spatial or habitat-related segregation of the sexes must be investigated before we can conclude that the bias is a trait of the western population. If the bias occurs in the population as a whole, then the effective size of the breeding population will be less than that indicated by counts. If the sexes segregate to different sites or habitats, then spatially constrained threatening processes may lead to a skewed sex-ratio.