The variation of male (n = 105) and female (n = 107) Southern Grey Shrike body mass has been analyzed in northern Spain during 2000-2002. The annual cycle was divided into autumn (October and November), winter (December to February) and breeding season (March to July), the latter subdivided into egg incubation, small nestlings and large nestlings periods. In order to analyze body mass, the residual index (RI) was used because it corrects body mass related to body size. The mean RI value for males was negative during the whole breeding season and positive during autumn and winter and it did not vary greatly between the periods. In females, the mean RI was definitely greater during egg incubation compared to other periods. The RI value of females was higher than that of males during the egg incubation and large nestlings periods, showing no significant differences in other periods. Female Southern Grey Shrikes (but not males) fitted to the programmed anorexia hypothesis during the breeding season whereas in winter they did not increase their body mass, in clear contrast to what has been put forward in some theoretical models.
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