Probability of site occupancy in the large heath butterfly Coenonympha tullia determined from geographical and ecological data

For threatened species that prove intractable to direct survey, there is a premium on being able to predict site occupancy using more readily availabl e site data. Herein, we use geographical and ecological data for Coenonymph a tullia from 148 sites surveyed in 1995-1996 to determine the probability of site occupancy in a further 33 sites surveyed in 1997. Discriminant func tion analysis using site-specific data on habitat quality and habitat area produces a 91% correct classification of the 148 sites surveyed in 1995-199 6 and a 79% correct classification for the 33 surveyed in suitable conditio ns during 1997. Data on site isolation does not improve the classification of sites. The difference in classifications between the year groups is sign ificant. It is caused by the unexpected (probability < 1%) absence of the b utterfly from three large, well-resourced sites at high altitude (> 400 m). The inference is that there is an altitudinal limit or effect (i.e. bienni al emergence pattern) to C. tullia in England. These results suggest that o ccupancy of Eriophorum-Erica mosses by C. tullia can be determined successf ully from habitat data for sites. However, in areas where site extinction h as progressed further, isolation is likely to be a more prominent factor. ( C) 1998 Elsevier Science Ltd. All rights reserved.