Non-breeding fæder Ruffs Philomachus pugnax associate according to sex, not morphology

Abstract

Capsule Fæders (males that are female look-alikes) associate with males rather than females, at several different spatial scales. Aims To test the prediction that the occurrence in space and time of fæders on ecological grounds should track that of females. Methods The fraction of fæders was estimated in five morphometric data sets that were collected over four decades in four different countries in three different seasons (comprising 9133 Ruffs). The regression of fæder–female fractions was tested against the null model assuming that the number of fæders is 1.0% of females. Results The fraction of fæders in catches averaged 1.03%, varying between 0.3% in autumn in the UK up to 0.85% in Sénégal in winter and 1.04% in The Netherlands in spring. On a stopover in The Netherlands the fraction decreased from 1.3% to 0.7% when the females started to arrive. At all four spatial and temporal scales the regression of fæder–female fractions deviated from the null model: we found high fractions of fæders in catches with low fractions of females, indicating that fæders rather associate with the larger-sized ‘normal’ males. Conclusion We suggest that fæders spend the winter, and migrate with, the larger-sized lekking males, and we propose that any survival costs associated with the use of suboptimal habitats is compensated by higher reproductive success as sneakers on leks.