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Individual study: A small population of New Forest burnet moth Zygaena viciae increases dramatically in response to the exclusion of sheep, in Western Argyll, Scotland

Published source details

Young M.R. & Barbour D.A. (2004) Conserving the New Forest burnet moth (Zygaena viciae (Denis and Schiffermueller)) in Scotland; responses to grazing reduction and consequent vegetation changes. Journal of Insect Conservation, 8, 137-148

Summary

The New Forest burnet moth Zygaena viciae is restricted to one small site in the UK, in Western Scotland. Its numbers declined between 1980 and 1990, down to at most 20 adult moths, apparently due to over-grazing. The larvae feed mainly on meadow vetchling Lathyrus pratensis. This study documents the effects of excluding sheep from the site, the location of which is undisclosed.

The site, approximately 1 ha of sloping grassland beneath cliffs, was first fenced in late winter 1990/1991. Damage to fences by wind and rock falls led to some sheep entering the site in early 1994 and again in 1996. From 1997 to 2004, sheep were effectively excluded.

Adult moths were monitored in July along a 5 m-wide transect running the length of the site (approximately 300 m). Population numbers were estimated by marking moths and recording recapture rates from 1991 to 2003 (moths were marked every year except 1992 and 1993).
 
Frequencies of nine flowering plant species were monitored in ten 1 m2 quadrats randomly selected within 10 x 10 m permanent quadrats, one outside and three inside the fence. A fifth 100 m2 quadrat within the fence was added in 1998. Plant monitoring was done in five years between 1991 and 2001 and the number of 1 m2 plots occupied by meadow vetchling across the entire site also recorded. Vegetation height was measured in three large quadrats inside the fence every year from 1990 to 2003.

From 1990-1996, the number of New Forest burnet moths remained low, between 0.2 and 1.2 adults/transect on average, with an estimated population between 10 and 24 individuals. From 1997 onwards, numbers increased dramatically, rising to 264 moths/transect and an estimated population size of 8,500-10,200 adults in 2003.

The plant community in the four large quadrats where grazing was excluded changed to include fewer plants of short grazed grassland (daisy Bellis perennis, white clover Trifolium repens and English stonecrop Sedum anglicum). The average vegetation height within the fenced area increased from 3.3 cm in 1990 to 20.2 cm in 2003. The average number of 1 m2 plots containing meadow vetchling/20 m grid square inside the fence increased from 5.4 in 1991 to 48.1 in 2001.
 
 
Note: If using or referring to this published study, please read and quote the original paper, the abstract of which can be viewed at: http://www.springerlink.com/content/l4425h3pr7834661/