BTO study shows why northern wrens trump their southern cousins in UK winters

A wren. Picture by John Harding/BTO

A wren. Picture by John Harding/BTO - Credit: Archant

One of Britain's smallest and most common songbirds, the wren, is prone to suffer through the country's cold winters.

But a new study shows those living further north are hardier than their southern cousins.

Research by scientists from the University of East Anglia and the British Trust for Ornithology, based in Thetford, has found that Scottish wrens are better adapted to survive colder winters than those in the south, with up to 5pc more body mass and a better ability to withstand hard frosts.

One of the report's authors James Pearce-Higgins, BTO director of science, said: 'This work indicates that each wren population is closely adapted to its local climate. There was a close correlation between the historic regional climate and the degree to which the population was resilient to severe winters.'

BTO researchers used information on wren populations collected by volunteers in the BTO/JNCC/RSPB Breeding Bird Survey, the main scheme for monitoring the population changes of the UK's common breeding birds.

Lead author Catriona Morrison, from the University of East Anglia, said: 'Large individuals are likely to be favoured in colder regions due to the thermal advantage of larger size and their ability to store more body fat, and our findings match the pattern seen more widely across other species – a pattern known as Bergmann's rule.'

Researchers have speculated that wrens are more adaptable than other bird species as they have shorter life spans.

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