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The MONARCH (Modelling Natural Resource Responses to Climate Change) report predicts that some species could benefit from the warming climate. The rare lesser and greater horseshoe bats are among them.

Wales is a stronghold for lesser horseshoe bats - a substantial amount of the UK, and even European, population is found in Wales.

Jean Matthews, bat expert at the CCW, said: "We're already seeing evidence of change with an increase in populations of some bats, including lesser horseshoes. The key seems to be that warmer winters allow more bats to survive and to be in better condition for breeding the following year."

The greater horseshoe bat is currently restricted to the south west of England and south Wales, with Pembrokeshire being its most northerly limit.

In recent years, however, an increasing number of greater horseshoe bats have been recorded wintering in north Wales. A minimum average spring temperature of 10C is required for birth to take place, so it's possible that a warming climate could result in them breeding there too.

Recently there's been a rise in reports of serotine bats in Wales. The species is largely restricted to the south of England in the UK, but they could be moving northwards due to the changing climate.

However, not all bat species have been increasing in number. Jean Matthews said: "Last summer [2007] was bad for bats with a combination of cool weather and heavy rainfall which meant that nursery roosts were too cold and it was difficult for mothers to find enough food for themselves".

Pipistrelles were particularly badly hit, and a lot of babies were abandoned, but numbers for all species may be down this year as a result of last year's cold. If the wet summers continue, the long term forecast for bats could be dismal.

However, not all bat species have been increasing in number. Jean Matthews said: "The summers of 2007 and 2008 were bad for bats with a combination of cool weather and heavy rainfall which meant that nursery roosts were too cold and it was difficult for mothers to find enough food for themselves".

Pipistrelles were particularly badly hit, and a lot of babies were abandoned. Lesser horseshoe bats that were caught as part of two studies were found to be underweight in autumn, threatening their overwinter survival and ability to breed the following year.

Although 2009 wasn't a barbecue summer, baby bats got off to a good start this year and the mild autumn means they are able to feed later in the season and build fat reserves to see them through the winter.

Results of bat monitoring by the showed an increase in the trends for some species in recent years, but because bats only have one young per year, they are still vulnerable to the effects of prolonged cool and wet weather in the summer.

Carolyn Davies