Previous studies of the consequences for breeding birds of climate change have explored how their populations may respond to increasing temperatures. However, few have considered the likely outcome of predicted extreme conditions and the relative vulnerability of populations in different habitats. Here, we compare phenology and breeding success in great tits and blue tits over a 10 year period, including the extremely harsh conditions during spring 2012, at three sites in eastern England – mixed deciduous woodland, riparian and urban habitat. Production, measured as brood biomass, was significantly lower in 2012 compared with the previous 9 years, with the decrease in productivity relatively greatest in woodland habitat. Production was related to hatch delay, i.e. birds not initiating incubation immediately after clutch completion, which was more common in 2012 than in previous years. The best predictor of hatch delay was daytime temperature (not nighttime minimum temperature) and rainfall, which convincingly reflected low growth and activity of caterpillar prey. We found that birds breeding in riparian and urban habitats were less vulnerable to the extremes of weather than those breeding in mixed deciduous woodland.

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when living in such highly modified secondary habitats (small woods, parks, farmland). Within-habitat heterogeneity (using the example of Monks Wood NNR) is generally associated with greater species diversity, but to benefit from heterogeneity at a landscape-scale may require both high mobility and the ability to thrive in small habitat patches. Modern landscapes, dominated by small, modified and scattered habitat patches, may fail to provide specialists, especially sedentary ones, with access to sufficient quantity and quality of resources whilst simultaneously increasing the potential for competition from generalists.

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