Mass-dependent predation and metabolic expenditure in wintering birds: is there a trade-off between different forms of predation?
Passerines maintain low levels of fat in winter even though larger fat reserves would provide better insurance against starvation. This is believed to be a result of predation risk and/or metabolic expenditure increasing with the amount of fat carried. Recent empirical studies indicate that the effect of increased mass on predation risk is small, but the effect on metabolic expenditure is large. U