Climate change: from egg laying to multi-taxa modelling

Juvenile Great Tit, photograph by Jill Pakenham

Data from our Nest Record Scheme are enabling an increased understanding of how climate change is affecting the timing of breeding in birds.

Working with the University of Edinburgh, more than 100,000 Blue Tit, Great Tit, Chaffinch and Pied Flycatcher nest records were analysed to understand how the timing of egg laying has responded to increasing temperatures. Each species advanced laying by 2-5 days for each 1 degree Celsius rise experienced during a 1-2 month species-specific window prior to laying. This window began later in spring for flycatchers than for tits, and later for northern populations of all species, indicating how different populations may show varying responses to warming, affecting their vulnerability to climate change. Comparison of responses between locations and years provided little evidence of adaptation to local climate; rather, individuals are able to adjust laying dates flexibly according to the spring temperatures they experience. The results suggest that populations may be sufficiently flexible to track projected increases in warming.

Work in collaboration with the Australian National University and the Netherlands Institute of Ecology used Nest Record Scheme data ( 1966-2013) for 35 species to examine how temperature-mediated changes in egg laying dates influence the number of fledglings produced per breeding attempt. Species exhibiting the greatest advances in clutch initiation displayed the greatest increases in productivity, but this did not translate to increased population growth, suggesting that processes such as over-winter survival may be relatively more important in determining abundance. Rising temperatures correlated with population growth rates of multi-brooded, but not single-brooded, species, suggesting that a greater proportion of individuals may be able to produce second broods under warmer conditions.

The final study, led by the Centre for Ecology and Hydrology and published in Nature, used data from 10,000 data sets on the timing of terrestrial and aquatic taxa, including egg laying from our Nest Record Scheme, to describe variation in species’ sensitivity to changes in temperature and precipitation. Importantly, given that birds can track temperatures flexibly, this work tests whether by doing so, they are able to keep pace with changes in the peak timing of their food resources. Predatory species (e.g. insectivorous birds) were less sensitive to changes in temperature than plants and herbivorous species (e.g. many insects), suggesting that spring warming has the potential to disrupt relationships between food demand and availability in delicately balanced natural systems.

Combined, these studies provide significant insight into how warming may influence bird populations. Whilst birds are able to adjust their timing of breeding in response to spring temperatures through behavioural plasticity, climate change may still disrupt their ability to keep pace with the effects of temperature as mediated by changes in the timing of plant growth or availability of insect prey. The effects on their populations will depend upon the combined impacts of climate change on breeding success and survival. These studies help us predict how species and communities may respond to future warming, and demonstrate the immense value of long-term monitoring, such as the nest record scheme, in being able to measure, understand and predict responses to ecological change.

Two of the studies were funded by the Natural Environment Research Council, whilst McLean et al. (2016) was funded by an Australian Research Council Future Fellowship.