Thermal and energetic consequences of nest location and breeding times in Water Pipits (Anthus spinoletta)

The thermal environment has pronounced effects on the energy costs of therm oregulation and affects an animal's allocation of energy to self-maintenanc e and parental care. Consequently, the selection of reproductive periods, b reeding habitats and nest-sites with a favourable microclimate can be advan tageous, especially for birds breeding in harsh environments. In this study on Alpine Water Pipits (Anthus spinoletta), we evaluate the importance of spatial and temporal factors on thermoregulatory costs by combining laborat ory measurements of metabolic rates under various temperatures with standar d operative temperatures (T-es) recorded in the field in different microhab itats. Using these measurements we estimate the thermal and energetic conse quences of nest locality and timing of reproduction. Our results show: (1) In the morning, T-es values were much higher on the east-north-east (ENE) s lope of a valley than on the west-south-west (WSW) slope; in the afternoon this pattern was reversed. As a consequence, energy costs (E-hour) for ther moregulation on the ENE slope were up to 0.6 RMR (resting metabolic rate at night) lower than on the WSW slope during morning hours and about 0.8 RMR higher during afternoon hours. (2) During the incubation and nestling phase s of first and second broods, total energy expenditure for thermoregulation in the daytime (E-daytime) was 0.2-0.3 RMR higher on the ENE slope than on the WSW slope. (3) Within slopes, E-daytime was lower during second broods than during first broods, with differences of 0.06-0.07 RMR during incubat ion and of 0.32 RMR during nestling care. These differences correspond to t he flying costs of females incubating eggs (0.09 RMR) and rearing nestlings (0.25 RMR). We conclude that nest placement in relation to microclimate ca n improve the female's energy budget, both in terms of the total daily expe nditure and its diurnal pattern. From thermal considerations alone, delayin g breeding into mid-summer would be advantageous, but this advantage is pro bably outweighed by the reduced chances for second and replacement clutches and by the necessity to complete moult before migration.