The average rate of decline of butterfly species in the British Isles has been high in recent decades, exceeding that of breeding birds or native vascular plants. Nearly a third of species, however, has increased, and several have expanded their ranges northwards. Some clear patterns are evident from these changes. Most losses are attributable to a decline of the specialised habitats required by the caterpillar stages in species' life cycles, either through fundamental ecosystem destruction, for example through intensive farming, or more subtle degradation, when surviving ecosystems have become shadier or more overgrown. The fragmentation of extensive breeding sites into small isolated patches has also been a major obstacle for some species. Climate warming, to date, has benefited all but the few northern species of butterfly, but is likely to become a major driver of decline in future decades. It was only after conservationists began to understand the causes of change in British butterflies that they were able to restore populations, through targeted land management, to former ecosystems. This process began successfully in the 1970s, and is probably responsible for the survival today of the Heath Fritillary, Silver-spotted Skipper and Adonis Blue.