Sex-biased mortality in the Lesser Black-backed Gull Larus fuscus during the nestling stage
Article first published online: 3 APR 2008
Volume 134, Issue 3, pages 237–244, July 1992
How to Cite
GRIFFITHS, R. (1992), Sex-biased mortality in the Lesser Black-backed Gull Larus fuscus during the nestling stage. Ibis, 134: 237–244. doi: 10.1111/j.1474-919X.1992.tb03805.x
- Issue published online: 3 APR 2008
- Article first published online: 3 APR 2008
- Submitted 13 August 199 1; revision accepted.31 October 1991
Theory predicts that skewed progeny sex ratios should be relatively common in vertebrate populations. In most birds this has proved hard to substantiate due to the difficulties associated with identifying the sex of large samples of chicks. This study reports the success of a new molecular DNA technique in determining the sex of 601 newly-hatched Lesser Black-backed Gulls Larus fuscus
There was no evidence of any adaptive sex ratio within broods. Male chicks were found to be disproportionately large and to grow at a faster rate than females. The overall sex ratio changed significantly from 0.484 (male/male + female) at hatching to 0.399 by fledging, probably due to male susceptibility to starvation. Mortality also increased significantly with hatching order, an effect often observed in species like the Lesser Black-backed Gull where hatching is asynchronous. I discuss the possibility that hatching asynchrony may in fact be a strategy employed to prevent excessive skews developing in progeny sex ratio whenever variable differential mortality is likely.
The results appear to vindicate Fisher's (1930) hypothesis which predicts the overproduction of the ‘cheaper’ sex. However, as the skewed sex ratio may be determined more by unpredictable environmental factors, such as food supply and weather conditions rather than parental strategy, this interpretation should be treated with caution.