Age Specificity in Territory Quality and Spatial Structure in a Wild Bird Population

I have published a fourth chapter from my PhD thesis. This paper examined whether birds of different ages tend to occupy different areas within a breeding population, and whether older individuals consistently breed in higher-quality territories. If age is spatially structured in this way, then variation in the age of breeders could potentially help explain why some areas of a population are consistently more productive than others.

Using long-term data from a wild great tit population, we compared the spatial distribution of breeder age with measures of territory quality and reproductive success. We found some evidence that age was associated with aspects of territory quality, but overall there was surprisingly little spatial structure in age. In other words, older and younger birds were not strongly clustered into different parts of the population.

This contrasted with both territory quality and reproductive output, which showed much clearer spatial patterns and were more consistent between years. One likely explanation is strong breeding-site fidelity among birds that survive from one year to the next, but also high levels of mortality and immigration. This creates considerable turnover in who occupies each territory and prevents stable spatial patterns in age from developing.
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The results suggest that differences in habitat quality are likely to be more important than the age of breeders in generating persistent spatial variation in reproductive success. More broadly, the study provides a framework for investigating spatial age structure in other species, and we predict that stronger patterns may emerge in longer-lived animals where individuals have more opportunity to accumulate in particular areas over time. The paper can be found here.