The effects of climate and habitat on breeding blue tits (Cyanistes caeruleus) and their prey

Abstract

Ephemeral resource and productivity peaks are characteristic of temperate woodland ecosystems. An ecological model system, which both exhibits and exploits these ephemeral peaks, and is the focus of this thesis, is the deciduous tree-herbivorous caterpillar-insectivorous bird food chain. Phenological synchrony within food chains, displaying ephemeral peaks, is crucial to maximise fitness of higher trophic levels. In the well-studied oak-winter moth-insectivore system, the phenology of all levels are highly temperature sensitive, and given atmospheric warming since the mid-20th century has been, and is predicted to continue, occurring at an unprecedented rate, this tri-trophic system is at risk of phenological mismatch. The effects of climate change on this system have been well studied in oak (Quercus spp.) dominated woodlands across Europe, as oak supports a wide variety of invertebrates. However, little is known about the importance of other deciduous tree species, which also support a variety of invertebrate species that are likely to be important to nesting blue tits (Cyanistes caeruleaus). Understanding the predictors of phenology and productivity across multiple trophic levels is required to understand the pressures on this food chain with a changing climate.
The overarching aim of this thesis is to explore the effects of both climate and habitat on the phenology and productivity of both blue tit and herbivorous caterpillars. The effect of tree leafing phenology and air temperature on herbivorous caterpillar phenology was investigated at a local scale, across an extensive woodland site in Durham (UK) through collecting fallen frass. Frass fall phenology was not predicted by temperature or tree phenology, and did not differ across four common deciduous tree species. However, frass fall was most abundant under oak trees, corroborating the importance of oak for Lepidoptera. Across the same Durham study site, nestling blue tits faecal sacs were collected, with a view of using next-generation sequencing to elucidate nestling diet and resource usage, to expand the food chain into a more complex food web. Due to difficulties extracting and amplifying DNA from blue tit nestling faecal sacs, sequencing was unable to be undertaken. However, I provide a method for extracting DNA from difficult faecal samples, which are likely inhibitor-rich and contain highly degraded DNA. The effects of climate and habitat on blue tit phenology and productivity were then considered, by combining bird nesting data from 34 sites across the UK with local temperature and habitat variables. Overall, climatic factors were more important predictors of blue tit phenology and productivity than habitat. Decreased clutch size and earlier breeding phenology, but decreased risk of nest failure, is predicted at higher temperatures. These results, combined, depict a mixed picture for how blue tits may fare with changing climate. To further work presented in this thesis, the effects of climate and habitat on recruitment need to be explored to understand the full implications of the results presented here on blue tit population dynamics.