Dunbar, R. I. M.; Anderson, R.; Knight, M.

Reproduction is energetically expensive for mammals, and especially so during lactation. In large-brained mammals such a primates, females invest heavily in additional feeding to fuel the costs of lactation. The evidence is more mixed in ruminant ungulates. We examine the foraging costs of lactating female feral goats living under environmentally challenging conditions in the northwest of Scotland where these effects are most likely to be exaggerated. We show, using data from three separate studies, that, compared to matched nonlactating females, lactating females do increase the time devoted to foraging, but only to a limited extent that is well below the theoretical requirements of their kids. Although they do not alter their diet, lactating females spend more time in shelter and at lower altitudes in order to reduce thermoregulatory costs. At high latitudes, the rate at which kids grow is such that females cannot afford to extend lactation much beyond two months. This will inevitably set a limit on ungulates capacity to produce large-brained offspring.