ORIGINAL ARTICLE Food supplementation and timing of reproduction: does the responsiveness to supplementary information vary with latitude? Stephan J. Schoech Æ Thomas P. Hahn Received: 16 March 2007 / Revised: 18 June 2007 / Accepted: 19 June 2007 / Published online: 18 July 2007 Ó Dt. Ornithologen-Gesellschaft e.V. 2007 Abstract Food supplementation usually advances the timing of laying. Here, we report a meta-analysis of 35 food supplementation studies demonstrating that species at high latitudes are less responsive to food supplementation than those at lower latitudes. Because the length of the breeding season varies with latitude, species at high lati- tudes may rely mostly upon photic cues and be less responsive to other environmental information. Lower latitude species, where times suitable for breeding vary from year-to-year, are predicted to be more responsive to ‘‘supplementary’’ information to adjust reproduction to coincide with conditions that favor the successful rearing of young. Studies by Wingfield et al. (Gen Comp Endo- crinol 101:242–255, 1996; Gen Comp Endocrinol 107:44– 62, 1997; Gen Comp Endocrinol 131:143–158, 2003) suggest a physiological underpinning to this reduced responsiveness to supplementary information in high-lati- tude species. Given that temperature increases resulting from global climate change are most pronounced at high latitude, reduced plasticity to respond to these changes in individuals of high-latitude species could cause high-lati- tude breeders to be poorly synchronized with a resource base that emerges earlier than usual. If high-latitude breeders indeed lack sufficient individual-level plasticity to cope effectively with climate fluctuations, effective opti- mization of reproductive timing in a rapidly changing environment would require similarly rapid evolutionary change. It remains to be seen whether this will be possible. Keywords Adaptive specialization Á Conditional plasticity Á Environmental cues Á Food supplementation Á Timing of reproduction Introduction It is critical that reproduction take place when environ- mental conditions are the most suitable, i.e., while condi- tions are relatively benign and resources, primarily food, are available for rearing young (Baker 1938). Animals rely on environmental cues that accurately predict favorable conditions and sufficient resources (i.e., selection favors utilizing reliable proximate components of the environment to time reproduction). While changing photoperiod reliably predicts changes that will occur over the longer term (‘‘initial predictive cues,’’ Wingfield 1980, 1983), there are also a number of proximate factors or cues that provide an animal with information on current conditions or changes about to occur over the short term (‘‘supplementary cues,’’ Wingfield 1980, 1983). The most important factor determining the timing of reproduction may be food. Lack (1968) proposed that clutch initiation is timed to assure sufficient food to feed dependent nestlings and fledglings, while Perrins (1970) subsequently proposed that the physiological needs of the female must also be considered. For many species, the production of the eggs alone requires a considerable output of energy, not to mention the production of repro- ductive tissues that are regrown seasonally. Clearly, both Communicated by F. Bairlein. S. J. Schoech (&) Department of Biology, University of Memphis, Memphis, TN 38152, USA e-mail: sschoech@memphis.edu T. P. Hahn Section of Neurobiology, Physiology and Behavior, University of California–Davis, Davis, CA 95616, USA 123 J Ornithol (2007) 148 (Suppl 2):S625–S632 DOI 10.1007/s10336-007-0177-6