Thursday, 28 March 2013

Changing times for dragonflies

Last summer was, by just about every measure, a poor one for our wildlife. Bird populations took a hit from a poor breeding season, butterflies were notable by their absence and many of our invertebrates fared badly under the cold and wet conditions. Such poor summers are, one would hope, the exception rather than the rule, so there is the opportunity for things to bounce back if they have a better breeding season this year. It is important, however, to view such short-term impacts against the long-term pattern of a changing climate and increasing pressures on the land. Some species will benefit from a changing climate but others will lose out and there is already evidence of differences in how well particular species, or groups of species, are likely to fare.

As a group, dragonflies appear to be doing well and they may be one of the winners from a changing climate. A number of species are expanding their breeding range northwards across Britain and others are in the process of colonising our region. Species like the small red-eyed damselfly, which first reached Britain in 1999, are now well established and spreading. The southern emerald damselfly, which exhibited a major influx at Winterton last September and which has been recorded from the site in six of the last 13 years, was noted egg-laying here in 2012. It has already bred at sites elsewhere in south-east England, most notably at Cliffe in Kent. The willow emerald is another recent colonist, now established across parts of Norfolk and Suffolk.

There are several other dragonflies that reach our shores from time to time, originating from populations breeding elsewhere in Europe and often far to the south. Such arrivals underline the dispersal powers of these often robust insects and the pattern of migration exhibited by some species. A good example of this comes in the form of two Suffolk records of large white-faced darter from 2012. This species has a relatively southern range compared to related species, and most populations tend to be rather small. An unexpected and rather large movement of this (and related species) was noted in 2012, with individuals recorded from sites across north-west Europe, including the British records from Dunwich Heath and Landguard. Such movements are likely to result from a good emergence, coupled with favourable weather conditions, that deliver individuals to areas beyond their normal range. If individuals arrive in good numbers at sites where suitable habitat is available then there is a chance that breeding may take place and the species become established. Under a changing climate, warmer conditions in Britain may further favour the establishment of more species with a formerly southern distribution, so it is very much a case of watch this space.

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