Stevenson IR, Bryant DM, 2000. Climate change and constraints on breeding. Nature 406: 366-367.

Although climate change apparently affects the breeding patterns of many animals, 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.