Body mass changes in female tawny pipits Anthus campestris during the nesting stage

We analysed female body mass change, corrected by tarsus length (body condition) in tawny pipits Anthus campestris during the nesting period in a population subject to high nest predation rates (between 70 and 85%), which leads to the need for replacement clutches. Decrease in female body condition over the nesting stage (6.8 g, around 27% of the initial mass during the whole nesting process) was related to laying date, clutch size and nesting period (incubation and nestling phases). Data from recaptured females indicated a decrease during each of the three nesting phases considered (the last days of incubation and first and last days of the nestling phase), with body mass always being higher in the first of the two measurements taken in each of these phases. The observation of a continuous decrease in body condition during the last days of incubation and first and last days of the nestling phase does not support the programmed anorexia hypothesis, but adjusts well to predictions of the stress hypothesis. These results suggest that the costs accumulated during the entire nesting stage in ground passerines subjected to high nest predation rates are linked to a superimposed effect of the cost of replacement clutches.