C

Brood size

Figure 8.6. Variance-sensitive provisioning in the common tern. (A) Parents travel back and forth between the resource point and the breeding colony, capturing a single fish on each trip from the size distribution shown. Parents can capture any encountered prey (shown as tactic 0) or can be progressively selective for larger prey (tactics 1-6). (B) The expected means and standard deviations in total daily delivery resulting from each prey selection tactic are shown here, and the "z-score" method ofStephens and Charnov (1982) applied to find the tactic minimizing the probability of a shortfall for brood sizes of 1, 3, and 5, indicated by tangents. The model predicts that as demand (brood size) rises relative to the expected delivery, parents should become more selective. (C) Prey choice of parental common terns. The graph shows the residual (with annual differences taken into account) prey size (with standard error) delivered in relation to manipulated brood size. (Data from Moore 2002.)

Brood size

Figure 8.6. Variance-sensitive provisioning in the common tern. (A) Parents travel back and forth between the resource point and the breeding colony, capturing a single fish on each trip from the size distribution shown. Parents can capture any encountered prey (shown as tactic 0) or can be progressively selective for larger prey (tactics 1-6). (B) The expected means and standard deviations in total daily delivery resulting from each prey selection tactic are shown here, and the "z-score" method ofStephens and Charnov (1982) applied to find the tactic minimizing the probability of a shortfall for brood sizes of 1, 3, and 5, indicated by tangents. The model predicts that as demand (brood size) rises relative to the expected delivery, parents should become more selective. (C) Prey choice of parental common terns. The graph shows the residual (with annual differences taken into account) prey size (with standard error) delivered in relation to manipulated brood size. (Data from Moore 2002.)

selection of prey for delivery, as well as the amount of self-feeding, but did not change their flight speed (i.e., workload). Moore (2002) interpreted the observed changes in prey selection, delivery time, and self-feeding as tactics

small prey (40mm3), >1 prey/load

small prey (40mm3), >1 prey/load

Woods large prey (110mm3), single prey/load

Woods large prey (110mm3), single prey/load normal nestling diet 50/50 by volume (% small prey delivered, by volume)

Deprivation Satiation

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