Abstract
The theory of trade-off between starvation and predation risks predicts a decrease in body mass in order to improve flight performance when facing high predation risk. To date, this trade-off has mainly been validated in passerines, birds that store limited body reserves for short-term use. In the largest avian species in which the trade-off has been investigated (the mallard, Anas platyrhynchos), the slope of the relationship between mass and flight performance was steeper in proportion to lean body mass than in passerines. In order to verify whether the same case can be applied to other birds with large body reserves, we analyzed the response to this trade-off in two other duck species, the common teal (Anas crecca) and the tufted duck (Aythya fuligula). Predation risk was simulated by disturbing birds. Ducks within disturbed groups were compared to non-disturbed control birds. In disturbed groups, both species showed a much greater decrease in food intake and body mass during the period of simulated high risk than those observed in the control group. This loss of body mass allows reaching a more favourable wing loading and increases power for flight, hence enhancing flight performances and reducing predation risk. Moreover, body mass loss and power margin gain in both species were higher than in passerines, as observed in mallards. Our results suggest that the starvation-predation risk trade-off is one of the major life history traits underlying body mass adjustments, and these findings can be generalized to all birds facing predation. Additionally, the response magnitude seems to be influenced by the strategy of body reserve management.
Highlights
The competition between two or more processes for the allocation of limited resources generally results in a trade-off that underlies different life-history traits [1]
Birds in both treatment groups showed body mass loss at least two times higher than that seen in control birds (Table 4), and body mass loss was higher in group 2 (G2) than in group 1 (G1) (Table 2)
The comparison of the food intake of a specific day with that recorded the same day of the previous or following week revealed negative correlations, indicating that if the food intake was high one day, it would be low 7 days later and vice versa. This means that food intake decreased during the disturbance and returned to its normal value after the disturbance ended (Figure 4b). We show in this experimental study that teal and tufted ducks responded to an increased predation risk by reducing food consumption and body mass
Summary
The competition between two or more processes for the allocation of limited resources generally results in a trade-off that underlies different life-history traits [1]. One important trade-off occurs for species acquiring food while avoiding predation [2,3]. Animals have to build up or maintain body fuel reserves which are an important buffer against starvation, especially when harsh winter weather conditions involve unpredictable food availability and energy requirements [4]. Assuming that maintaining a high level of body fuel, i.e. a high body mass, incurs a significant cost in terms of enhanced mortality risk due to predation vulnerability [5], the amount of body reserves that a bird carries has generally been viewed as a trade-off between the risk of starvation and the risk of predation [6,7]. Body mass adjustment is considered to be the consequence of this trade-off
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