The breeding ecology of the blue tit in relation to temperature microclimate

Abstract

With warmer springs we observe earlier Spring phenologies. Long-term trends for earlier phenologies in warmer years have been demonstrated using population mean responses against temporal, altitudinal and latitudinal gradients. Temperature driven changes in phenology are measurable in a model system such as the oak-caterpillar-blue tit and the degree of change from one trophic level to the next can be compared across the network. The majority of studies on such a system focus on population mean trends. In this study I construct a geospatial model of temperature microclimates and test if variation in the phenologies of the simple oak, caterpillar, blue tit ecological network corresponds to variation in temperature across a single study site. Temperature traces are

predicted with relative ease to a robust degree using the statistical modelling approach and given the known environmental, seasonal and synoptic weather trends for the location and time of interest. A microclimate modelling approach removes the constraint of a restricted temperature data-collection period and data is not limited to the site or position of the logger. This enables the comparison of behavioural responses amongst individuals as well as within individuals. I demonstrate that similar patterns of phenology are observed across the microclimates of a single study system as are observed for the same study system over time. More importantly by creating individual-specific temperature profiles I am able to compare the phenologies at each stage of the network to different temperature regimes as they occur under natural conditions. I find that not only do the three trophic levels differ in their periods of sensitivity to temperature change, but also that within these time-windows the phenologies of the tree, herbivore and bird are associated with differing temperature parameters. In addition to an effect on the timing of breeding, I also find an effect of microclimate temperature on incubation behaviour and female condition across the breeding effort. Climate change can lead to the uncoupling of links within ecological networks, known as trophic mismatch, as the environment of cue perception becomes disassociated from the environment of peak energy demand and selection. Given that the different trophic levels are sensitive to temperature change during different phases of Spring, I explicitly test whether temperature regimes are consistent across the Spring season and what impact differing temperatures between phases has on the breeding success of the apex predator. I find that not only are different temperature parameters not collinear, but that temperature changes are not concomitant across the Spring season. I therefore find support for the theory that trophic mismatch and blue tit nesting success is not just driven by warming temperatures, but by when temperature change occurs.