FOOD, FEATHERS AND FLUCTUATING ASYMMETRIES

Nutritional, or energetic, stress has been implicated as a causal fact or in the inter-individual differences in levels of fluctuating asymme try in the elongated tails of male swallows (Hirundo rustica). However , there has been no direct experimental test of this hypothesis. We re port results from an experiment that has investigated the effects of s equential food deprivations on levels of fluctuating asymmetry in prim ary feathers and chest plumage of the moulting female European starlin g (Sturnus vulgaris). Birds were housed individually and taken through their full moult by means of photoperiodic manipulation. During this period, some of the birds experienced food deprivations. At regular in tervals, we recorded the length of every primary feather, quantified t he chest plumage via video-image analysis, and recorded body mass and subcutaneous fat score measurements. We found that increasing levels o f nutritional or energetic stress caused larger development asymmetrie s, which would appear to have increased fitness costs. Primary feather asymmetry showed a negative relation with amount of subcutaneous fat stored during moult and a positive relation with social dominance. Thi s is the first study to show, directly, the importance of energetic st ress in the production of feather and plumage asymmetries. Low levels of feather asymmetries were also associated with an indicator of repro ductive status (chest 'spottiness'). These findings support the recent literature, suggesting that degree of fluctuating asymmetry, even in traits under stabilizing selection, may reveal aspects of individual f itness value.