Local extinction of British farmland birds and the prediction of further loss.
Abstract
The populations of many UK farmland birds declined between 1970 and 1990, frequently accompanied by contractions in breeding ranges. Ornithological atlas data, land use data and environmental data at the scale of 10-km squares were used to investigate the relationship between local extinctions and habitat suitability for six species (grey partridge, lapwing, turtle dove, tree sparrow, reed bunting and corn bunting), and to predict where future losses are most likely. For each species we tested the hypothesis that local extinctions were concentrated in environments that were inherently less suitable. We also tested the hypothesis that spatial patterns of loss were not independent between species due to their concurrence in the same habitats. Multivariate analyses (PCA) showed that areas where each species became extinct between 1970 and 1990 were more similar in land use type, climate and topography to areas where a species was never present than those where it was retained; local extinction was more likely in less suitable environments. Multiple logistic regression showed that for five of the six species the environmental gradient best predicting presence or absence in 1970 was also that best predicting loss between 1970 and 1990. For the six species studied, local extinctions were least likely in lowland arable areas. For any pair of species, local extinctions were more frequent outside the area of overlap of the two species' ranges than inside. Within the area of overlap, species tended to be lost from the same squares. For each species, likelihood of local extinction declined with increasing number of the other five species present. We used model parameters to map the probability of future local extinctions of the six species considered, allowing the identification of key areas for conservation management at a spatial scale appropriate to agri-economic incentives.