Theoretical models of adaptive energy management in small wintering birds

Abstract

Many small passerines are resident in forests with very cold winters. Considering their size and the adverse conditions, this is a remarkable feat that requires optimal energy management in several respects, for example regulation of body fat reserves, food hoarding and night-time hypothermia. Besides their beneficial effect on survival, these behaviours also entail various costs. The scenario is complex with many potentially important factors, and this has made 'the little bird in winter' a popular topic for theoretic modellers. Many predictions could have been made intuitively, but models have been especially important when many factors interact. Predictions that hardly could have been made without models include: (i) the minimum mortality occurs at the fat level where the marginal values of starvation risk and predation risk are equal; (ii) starvation risk may also decrease when food requirement increases; (iii) mortality from starvation may correlate positively with fat reserves; (iv) the existence of food stores can increase fitness substantially even if the food is not eaten; (v) environmental changes may induce increases or decreases in the level of reserves depending on whether changes are temporary or permanent; and (vi) hoarding can also evolve under seemingly group-selectionistic conditions.

How climate change might influence the starvation–predation risk trade-off response

“…Empirical work described above, and theoretical models, have demonstrated that mass gain in response to predation risk is likely to be an advantageous strategy associated with favourable foraging conditions (e.g. McNamara et al 2005;Brodin 2007) and thus increasing populations (MacLeod et al 2007). As winter temperatures increase, great tits can afford to avoid predators in time and space, can afford to carry higher fat loads despite the increased metabolic costs they entail and, if foraging conditions suddenly become worse (i.e.…”

Stochasticity and controllability of nutrient sources in foraging: host‐feeding and egg resorption in parasitoids

“…The situation was identical fifteen years ago, when McNamara et al (1994) published their seminal theoretical study on foraging routines of a small bird in winter: there was a lack of empirical data to provide a test of their theory. Nevertheless, their study spurred a whole sequence of refined experiments and adjusted models making ''the small bird in winter'' one of the best understood cases of optimality applied to behavioral ecology (Brodin 2007). A similar effort is needed to understand foraging routines in parasitoids, and we hope that our model will encourage the collection of observations and design of experimental tests.…”

Adaptive winter survival strategies: defended energy levels in juvenile Atlantic salmon along a latitudinal gradient

“…photoperiod; McNamara & Houston 1990;Macleod et al 2005;Brodin 2007;Polo et al 2007). Cyclic daily patterns of fattening and starvation are found in small birds during winter, and photoperiodic responses suggest fine-scale adjustments of energy reserves (Polo et al 2007).…”

“…Animals typically draw on reserves in the form of stored lipids in adverse periods when energy intake does not match the demand or when feeding is risky. As acquiring and catabolizing lipid reserves imposes costs, energy reserves are usually maintained below maximum levels (Witter & Cuthill 1993;Brodin 2007;Macleod et al 2008). Several vertebrate groups are known to tailor their levels of storage lipids according to shortand long-term energy demands and to regulate their energy intake based on a projected energy state at the expected end of the adverse period (Bull et al 1996;Polo et al 2007).…”

“…A classic example is the effect of the level of storage lipids on feeding under predation risk (McNamara et al 2005;Brodin 2007). Animals typically draw on reserves in the form of stored lipids in adverse periods when energy intake does not match the demand or when feeding is risky.…”