Mammals of Wytham Woods, Oxfordshire
by Dr. Chris Newman (Oxford University's Wildlife Conservation Research Unit)
Earthwatch-supported project 'Mammals of Wytham Woods', led by Dr. Chris Newman, recorded higher mortality among the badger population in Wytham Woods near Oxford due to exceptionally dry springs in 2002 and 2003. The deaths are occurring particularly among badger cubs, which don't have enough body mass to survive droughts.
Although these climate-related deaths have reduced the Wytham population to 250 from 300 in 1997, as a whole UK badger numbers have soared in the past 15 years, also generally attributed to climate change. Milder and wetter weather is causing more earthworms to come to the surface in the autumn, providing a valuable source of food for the badgers. At Wytham Woods, there was an increase from 100 to 300 animals in the decade leading up to 1997.
Here Dr. Chris Newman describes how his research is contributing to knowledge on how badgers might be affected by climate change.
1. Some people might say that the climate change was having a good effect ie increasing badger numbers - what do you think?
The flip-side of mild winters is summer drought. Currently adult badgers have enough body-mass to survive summer droughts, by diversifying from earthworms and eating insects, fruits, cereals etc (but this means foraging further afield, increasing risks of traffic accidents). Cubs, however, are too small to survive severe droughts and too inexperienced to find diverse food sources away from familiar areas once they're weaned. Also, dry spring weather (and in 2002/2003 March and April were exceptionally dry) means that lactating females struggle to find enough food to meet the energetic costs of producing milk. As competition between lactating females intensifies they can ultimately reach a point where they kill each others' cubs to reduce competition.
So currently, adults are benefiting, but it's getting harder for badgers to replace those that are dying of old age...if it gets even slightly dryer or hotter over spring/summer the whole dynamic of the badger population could tumble into decline.
2. What are the main risks to badgers?
The biggest risk is road traffic accidents - up to 50,000 badgers are run over every year. And some sources suggest up to 9,000 badgers a year are still being killed illegally by baiting and unlicensed sett destruction.
Many cubs die from infection by parasites which cause diarrhoea - the effects of this are exacerbated by drought as the cubs are unable to replace the fluids lost. A good age for a badger is 8+ and about 2% live into their teens. 50% of cubs born die by the time they're 2 ½.
3. How will knowing about the effects of climate change help us protect the species?
By observing climatic trends we can predict the "risk" the population is at e.g. a spring drought or a cold frosty winter is a cause for concern. By observing whether you get several 'good' or 'bad' years in succession you can predict the dynamic state of the population. Obviously, if things get dryer/worse then greater protection, such as better road mitigation for new and existing roads, would be needed.
4. Are you doing any further research into the effects of climate change on the badger population or other species you study?
We also have some data on how field voles are affected. When we have long, dry, hot summers, the grasslands become parched - and field voles only eat fresh grass. Also, once the grass wilts it no longer provides good shelter or protection from predators. In "normal" years, sheep grazing benefits voles by stimulating new grass growth, so you get highest vole densities in sheep pasture. In "dry" years the sheep eat the grass down to the roots and the voles suffer - so reducing sheep grazing pressure is important for vole conservation in drier conditions.
Tawny owls eat up to 40% of worms in their diet....combine [a reduction in the number of worms] with a lack of field voles and they'd be in trouble too - very quickly!
5. What is your view on what might happen in the future - say, over the next ten or fifteen years?
Hard to predict, but if you string a series of harsh years together it obviously adds up to bad news. Five or seven dry weeks in the summer makes an enormous difference. It could lead species to diversify into other food sources, possibly causing more crop damage, more garden damage or more orchard raiding.
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Editors Notes