A Lesson in Habitat Management
By Dr. Gerard Cheshire
Back in 1979 the Nature Conservancy Council declared the Large Blue (Phengaris arion) butterfly extinct in Britain. There was a tragic irony attached, as the NCC had inadvertently finished the butterfly off in its attempt to save the species. The reason was naivety about specific ecological requirements for the Large Blue, so conservationists simply erected fences around its remaining habitat, as an effort to protect the butterfly from disturbance and from collectors. This well-meaning action led to the habitat becoming overgrown, rendering it unsuitable for the butterfly’s lifecycle as the high sward prevented the ground from warming sufficiently. In 1984 a successful reintroduction program was begun, by collecting Large Blue stock from a Swedish island and introducing grazing regimes on appropriate sites. As the source population lived at a northerly Scandinavian latitude the ‘Swedish Blue’ – not to be confused with the ‘Norwegian Blue’ – readily took to its warmer new home and has now established itself very well indeed.
This cautionary tale is useful to remember in apprehending that many butterfly species have subtle but important habitat requirements that need to be met for conservation efforts to succeed. Moreover, understanding those habitat requirements often requires detailed scientific study and experimentation in the field and laboratory. As many British butterfly species seem to be in population decline, then there is no better time to consider being involved with this essential research.
Changes in land use and farming practices mean that the British landscape no longer comprises the traditional patchwork of environments that used to provide adequate habitat sites for butterflies without the need for intervention, as is still the case in France. So, the only way forward is by carefully managing habitats to ensure their suitability, which means knowing what kind of management is required.
Knowing the basic requirements of a species, such as its larval foodplant and the general behaviour of the adult is only half the story, as the devil is in the detail. As a butterfly pair require only two offspring to survive for the population to remain stable, then clearly many more offspring perish in the process. It therefore takes only a subtle change in habitat characteristics to tip the fortunes of the population in one direction or the other. Butterflies have evolved to be good at recovering their numbers following bad years, but only if the available habitat is right for them, or if they can relocate to another suitable habitat site.
Other British butterfly species that have benefited from habitat management include the White Admiral (Limenitis camilla), the Marsh Fritillary (Euphydryas aurinia) and the High Brown Fritillary (Argynnis adippe). Each live in a different habitat type and have their own species-specific idiosyncrasies, making them rather susceptible to decline if things aren’t quite right for them.
In contrast, the species often seen in our gardens are common either because they are less sensitive to anthropomorphic change or because our gardens can actually offer suitable habitat. The larva of the Comma (Polygonia c-album) used to feed primarily on hops and became fairly scarce with the decline in hop growing, until a population converted to eating stinging nettles which are, of course, found growing in many gardens. It goes without saying that the Large White (Pieris brassicae) and Small White (Pieris rapae) are common because they feed on cabbages, although they will now readily eat nasturtiums too.
Of the sixty British butterfly species, only about twenty can be considered common or garden species. The remaining forty have more specific habitat requirements, with a number of those habitats becoming rather scarce for various reasons – agricultural monoculture, livestock farming, timber plantations, urban development, road and railway building, neglect & succession, arboreal disease, and so on.
In that light, choosing a career in butterfly conservation can be very rewarding, whether involved with the scientific investigation or involved with the implementation of habitat reconstruction and management. To some extent, there is always overlap between the two, simply because trial and error is required for finetuning procedures. When it succeeds there is nothing more gratifying than seeing a healthy butterfly population going about its business as if the managed habitat were completely natural in its composition and maintenance. Therein lies the reward for one’s enthusiasm and labour.