Are there thermoregulatory constraints on the timing of pupping for harbour seals?

In this paper we describe a detailed model of the thermal balance of a seal in air. We tested the model against the limited experimental information a vailable on thermoregulation for harbour seals (Phoca vitulina) in air. Sin ce a mother must meet both her own and her pups' energetic costs, we sugges t that there may be an energetic advantage for harbour seals in Scotland if lactation is timed to coincide with the most favourable conditions for hau ling out. To test this hypothesis, we used the harbour seals in the Moray F irth as our case study. The model does predict an energetic cost resulting from thermoregulation during haul-out for a mother and her pup in the Moray Firth. Taking the mother and pup as a unit, we estimate the minimum cost d uring lactation. This combined cost, which must be met by the female seal, is similar to the minimum metabolic rate during haul-out for the summer pre dicted from the model. In winter the predicted minimum metabolic rate excee ds the lactation cost, and an additional cost of thermoregulation results. The model predicts the most energetically favourable time for lactation to be June and July, and this is coincident with the timing of pupping in this seal population. We suggest that for harbour seals in Scotland, the timing of pupping may be influenced by the thermoregulation costs of haul-out. Th is provides indirect evidence that thermoregulation influences haul-out beh aviour in this small phocid species.