Bill, bum or bellow: comparing four methods for sexing Wedge-tailed Shearwaters

Stephen Totterman (Empire Vale, New South Wales, Australia) has published early on-line in the journal Marine Ornithology on sexing Wedge-tailed Shearwaters Puffinus pacificus.

The paper’s abstract follows:

“Identifying female and male birds can be very helpful in field studies.  However, sexual differences in size and plumage are subtle in most petrels.  Four field methods were compared for sexing breeding Wedge-tailed Shearwaters Puffinus pacificus on Muttonbird Island, New South Wales, Australia: cloaca inspection, biometrics, acoustics and playback-response. Accuracy was evaluated against molecular tests.  A biometric discriminant function combining bill depth and total head length sexed 81% of birds (79 of 98) correctly.  Males averaged 3% larger than females, with overlapping size ranges.  Sexual differences in cloacal size were not always obvious because female cloacae gradually relapse after laying and males struggling in the hand can present extruded cloacae.  Cloacal sexing was 86% correct (93 of 108 birds).  Withinpair comparisons of biometrics and cloacal size increased sex classification accuracy for twice the effort (two birds evaluated rather than one).  An acoustic discriminant function combining fundamental frequency and note length from burrow call recordings sexed 97% of birds (102 of 105) correctly.  A novel playback-response test was efficient and sexed 94% of birds (47 of 50) correctly.”

Wedge-tailed Shearwaters

Reference:

Totterman, S.L. 2015.  A comparative evaluation of four field methods for sexing Wedge-tailed Shearwaters Puffinus pacificus.  Marine Ornithology 43: 83-93.

John Cooper, ACAP Information Officer, 16 April 2015