Spatial variation in avian phenological response to climate change linked to tree health

While there is overwhelming evidence for phenological responses of animal and plant populations to climate change, most studies have been conducted at the level of entire populations, thus neglecting the scale at which much selection operates and at which animals and plants respond to their environments. Here, using data from a 60-year study, we demonstrate marked small-scale spatial variation in the rate of change in timing of egg laying in great tits (Parus major). We show, further, that this variation is linked to changes in the health of a key primary producer, oak (Quercus robur). The existence of small-scale spatial variability in responses to climate change has important implications for understanding the extent to which local adaptation and phenotypic plasticity govern responses to climate change and for the role of behavioural responses such as habitat selection and dispersal in ameliorating challenges due to climate extremes. Climate change–induced shifts in seasonal events are often studied at population levels, which can neglect the scale at which selection operates. Here, the authors show marked small-scale spatial variation for egg-laying timing of great tits and further link these changes to the health of nearby oaks.