Dispersal characteristics and management of a rare damselfly

1. Coenagrion mercuriale is a rare damselfly in Britain and mainland Europe and has been declining in the last 30 years. It has specialized habitat requirements and has been viewed, traditionally, as a poor disperser. Knowledge of its dispersal ability was considered in its Biodiversity Species Action Plan as essential for the formulation of appropriate conservation management strategies. 2. Mark-release-recapture (MRR) studies of C . mercuriale in two large UK heathland populations were undertaken. Mature adults had a low rate of movement within continuous areas of habitat (average < 25 m movement), low emigration rates (1.3-11.4%) and low colonization distances (maximum 1 km), all comparable to similarly sized coenagrionids. 3. Movements were more likely within than between patches of suitable habitat over short to medium distances (50-300 m). Between-patch movements were more likely between patches that were close together. Scrub barriers reduced dispersal. 4. The probability of dispersal between two recaptures depended on the length of the time interval between them. Coenagrion mercuriale performed considerable between-patch movements within a small fraction (1-2 days) of its mean mature adult life span (7-8 days). 5. Qualitative comparison of field colonization distances measured here and distances between UK sites occupied by C. mercuriale revealed that empty sites within large clusters of sites would probably be recolonized rapidly and dispersal events would be frequent. However, such events would occur rarely within small isolated sites or clusters of sites, leaving local populations prone to extinction. 6. Synthesis and applications. These data show that management effort should be directed towards maximizing the likelihood of C . mercuriale recolonizing sites naturally within 1-3 km of other populations (particularly within large clusters). Scrub boundaries should be removed between existing populations and empty, but suitable, sites to facilitate stepping-stone dispersal movements.