A method for assessing changes in the abundance of butterflies

Pollard, E.

Biological Conservation 12(2): 115-134

1977


ISSN/ISBN: 0006-3207
DOI: 10.1016/0006-3207(77)90065-9
Accession: 004583173

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Abstract
A method based on transect counts has been developed to assess changes in abundance of butterflies from year to year. The method involves weekly walks around a transect route making counts of butterflies seen within defined limits. The transects are divided into sections related to habitat or management units. Walks are made only when weather conditions satisfy specified minimum requirements. The method has been tested for 3 yr at Monks Wood [Cambridgeshire, England] and for 2 yr at a number of other sites. The basis for annual comparisons is an index of abundance which is produced for each brood of each species, except when separation of broods is not possible. This index is correlated with abundance, although the precise nature of the relationship will vary from species to species. Evidence on this presented for 2 spp. [Pararge aegeria (L.) and Coenonympha pamphilus (L.)]. The method makes it possible to monitor the abundance of butterflies at selected sites, using recorders, such as nature reserve wardens, who can fit in 1 or 2 h recording each week when the weather is suitable. Such a scheme, based on the methods described in this paper, began in 1976. In addition to the monitoring of fluctuations of abundance, the method provides considerable information on the phenology and ecology of butterflies. The division of the transects into sections makes some assessment of the effects of habitat change, due to management or other factors, possible.