The effect of nestling condition on risk-taking in meadow pipits

The harm to offspring hypothesis, which says that parental investment should be related to the harm that offspring without parental care would suffer, was tested on meadow pipits, Anthus pratensis. We placed a stuffed European weasel, Mustela nivalis, 5 m from seven nests with exothermic 1-3-day-old nestlings. We measured air temperature and the cloacal temperature of the nestlings at the start of the trial and the time elapsing between the removal of the weasel model and the parent's first entry into the nest. We compared pairs of trials at each nest when nestling condition was good (normal cloacal temperature) and when it was temporarily poor (reduced cloacal temperature). The hypothesis predicts a shorter elapsed time when nestling condition was poor. In all cases the females entered the nest before the males and entered more quickly when nestling condition was poor. The results thus supported the harm to offspring hypothesis. (C) 1997 The Association for the Study of Animal Behaviour.