Individual activity rates in wintering Eurasian woodcocks: starvation versus predation risk trade-off?

Wintering birds face a trade-off between starvation and predation risk. In Eurasian woodcocks, Scolopax rusticola, habitat use may reflect this trade-off because meadows, where most birds spend the night, are characterized by a higher risk of predation and a higher biomass of food (earthworms) than the woods, used by day. We monitored activity of 34 woodcocks fitted with tiltswitch radiotags Young birds were more active than adults, probably because they were less efficient at foraging. In general, nocturnal activity was inversely correlated with air temperature and with daylight foraging activity, suggesting some compensatory mechanism, modulated by thermoregulatory constraints. Individual activity patterns differed, and we classified woodcocks according to three main wintering strategies: 'always', 'sometimes' or 'never' visiting fields at night. The decision to fly to fields at night seemed to be taken every evening according to the amount of daylight foraging activity in woods and the air temperature. After feeding in a rich patch of food on a mild day, woodcocks did not have to risk going to meadows. Conversely, in patches of fewer food resources or at lower temperatures or both, woodcocks could not meet all their energy requirements without going to fields at night (where there was always sufficient food) and eventually, changing their diurnal sites. Therefore, the trade-off between feeding and predation risk depends on how efficiently birds find a rich patch of food in the forest and exploit it optimally during the day. (C) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.