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Brief Communications

Nature 406, 366-367 (27 July 2000) | doi:10.1038/35019151

Avian phenology: Climate change and constraints on breeding

Ian R. Stevenson & David M. Bryant1

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Although climate change apparently affects the breeding patterns of many animals1, 2, 3, the wider implications for breeding success are unclear. Here we describe an energy trade-off between reproduction and maintenance that occurs during cold weather in great tits (Parus major L.), pointing to a thermal constraint on the timing of egg laying. Our observations indicate that the fine-scale pattern of climate change could be critical to the reproduction of some species and underlies previously unexplained variation in the breeding success of other temperate birds.