SCHOECH, S.J.*; HAHN, T.P.; Univ. of Memphis; Univ. of California, Davis: Timing of reproduction and food supplementation: Are high latitude species less responsive than low latitude species to non-photic cues?

Food supplementation usually advances the timing of egg laying in birds. A meta-analysis of 34 food supplementation studies suggests that high latitude species are less responsive to food supplementation than lower latitude species. As the length of the breeding season varies with latitude, it may be that species at high latitudes with a short season rely largely upon photic cues. In contrast, lower latitudes have a longer suitable period at which breeding can occur and this may lead species to be more responsive to �supplementary� cues, thus assuring suitable conditions for rearing young. Studies by Wingfield et al. (1996, 1997, 2003) suggest a physiological underpinning to this reduced responsiveness to supplementary cues in high latitude species. Given 1) temperature increases resulting from global climate change are most pronounced at high latitude and 2) the apparent reduced plasticity to respond to these changes in high latitude species, one might predict that these species will have difficulty synchronizing reproduction with a resource base that will emerge earlier than usual. Should global climate change advance the time when the critical resources for the rearing of young are available, high latitude species may not have the plasticity to adapt to the change in the time when conditions are optimal for breeding. As Visser et al. (1998) note in their studies of breeding of great tits, decoupling of resources and breeding may be in part because the sites from which birds migrate do not reflect the environmental changes that have occurred on the breeding grounds. Even if they could respond to the earlier emergence of resources, they might not arrive from overwinter sites early enough to take advantage of the earlier resource availability.