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Too many sheep spoil the eggs

15 June 2005

Knowing something about the climate of the forthcoming winter could help the NHS to plan ahead and cope more efficiently with a range of winter health situations, new research results show.

Too many sheep in Britain’s uplands could be responsible for the decline of some native birds according to research published today in the journal Biology Letters.

The research, led by Dr Darren Evans from the Centre for Ecology & Hydrology in Banchory, provides the first hard evidence of a link between increased sheep grazing and the breeding patterns of the meadow pipit, Britain’s most common upland bird.

The researchers examined the effects of sheep grazing on egg sizes of these ground-nesting birds. They varied sheep numbers in an upland field experiment and found that areas with high sheep numbers had meadow pipit nests with the smallest eggs, and that areas with low sheep numbers had nests with the largest eggs.

Dr Evans explained, "Egg size is important for many bird species as chicks that hatch from large eggs tend to grow faster and have a better chance of survival than those that hatch from small eggs. We believe that high sheep numbers reduce food supplies and with less food around, adult birds are unable to produce the large eggs necessary for well-nourished, healthy chicks."

He added, "Livestock grazing is important for maintaining the character and biodiversity in upland areas. But sheep numbers in Britain have more than doubled in the last 50 years. Our results suggest that intensive livestock grazing appears to be bad for birds, whereas smaller numbers of sheep could be good for them. Eggs laid in ungrazed areas were also small, indicating that either too many or the complete removal of sheep in upland areas might have a detrimental effect on pipit breeding performance. We need to get the balance right."

The study was carried out at Glen Finglas in Central Scotland during 2002 and 2003. It could help to explain the observed link between increased grazing and declines in grassland birds in both Europe and North America.

Further information

Barnaby Smith
Centre for Ecology & Hydrology press office
Tel: 07832 160960

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

Notes

1. The paper, ‘Livestock Grazing affects the egg size of an insectivorous passerine’ will be published in the June issue of the Royal Society journal Biology Letters. The paper will go online on Wednesday 15th June. This initiative was intended to complement other research supported by BBSRC, NERC and other funding bodies by supporting research into the underlying mechanisms of basic biological processes.

2. Dr Darren Evans is an Avian Ecologist based at the Centre for Ecology & Hydrology in Banchory, Scotland.

3. The work was carried out as part of the ‘Effects of Grazing on Upland Birds (GRUB)’ project funded by the Scottish Executive Environment and Rural Affairs Department.

4. The Centre for Ecology & Hydrology (CEH) is the UK's leading research organisation for land and freshwater science. Its 500 scientists carry out research aims to improve our understanding of both the environment and the processes that underlie the Earth's support systems. It is one of the Natural Environment Research Council's research centres. CEH has 8 research sites within England, Scotland and Wales and an administrative headquarter based at Swindon.

5. NERC is one of the UK's research councils. It uses a budget of about £300m a year to fund and carry out impartial scientific research in the sciences of the environment. NERC trains the next generation of independent environmental scientists. It is addressing some of the key questions facing mankind such as global warming, renewable energy and sustainable economic development.

Press release: 25/05