Deer Behind Britain's Great Bird Decline?
James Owen in the United Kingdom
for National Geographic News
|March 3, 2003|
This spring leading ornithologists will begin surveying bird life in 350 woods across Britain. The study aims to reveal the reasons for a startling decline in many woodland species.
Since the 1970s the woods have been losing their spring chorus of birdsong. Willow tit numbers have fallen 78 percent, woodcock by 74 percent, and song thrushes have more than halved. This is despite a significant increase in tree coverup more than 20 percent in England alone over the last two decades.
Possible causes for dwindling bird populations include changes in forestry practices, egg predation by grey squirrels, and the effects of climate change. Yet the chief suspect in the minds of many ornithologists is that picture of doe-eyed innocencethe deer.
Deer numbers are soaring in Britain. Two hundred years ago the roe deer was extinct in England and Wales, the victim of over-hunting and forest clearance. Today the population stands at around 700,000.
It's a similar story for the red deer, Britain's other native species, which now festoons many Scottish hillsides.
The growth in tree cover, increased cereal farming (an important source of food), reduced hunting levels, and better winter survival rates due to a warming climate are all thought to be factors behind the deer's revival. The same goes for two introduced deerthe fallow and muntjacwhich are now widespread in Britain.
The two conservation nonprofits behind the survey, the Royal Society for the Protection of Birds (RSPB) and the British Trust for Ornithology (BTO), say these four species are chewing away huge chunks of woodland bird habitat.
"Birds like nightingales and warblers are adversely affected," said Rob Fuller, BTO's director of habitat research. "They need low, dense vegetation in which to nestdeer remove this.
"We also think deer have a negative impact on food resources. By biting off buds and flowers they reduce the amount of seed and fruit available in autumn and winter."
Plant Variety Is Crucial
Deer can alter the entire structure of a wood. Certain flowers, shrubs, and trees are pruned back, leaving only less palatable species. Fuller says plant variety is crucial to maintaining the diversity of other woodland wildlife.
"The woods where I work in England contain roe and muntjac deer," Fuller said. "The plants they really clobber include ash, hazel, and sallow. And it's characteristic of all woods with high deer densities that bramble gets heavily browsed. That's bad news for birds as many of them love bramble."
Wytham Wood in the county of Oxfordshire, England, has lost much of its bramble. In the early 1970s this thorny shrub covered 35 percent of the wood. Today the figure is six percent. The decline in bramble cover has been matched by many bird species. During the same period fallow deer numbers multiplied from a dozen or so to over 250.
Birds suffering the steepest falls include the blackbird, dunnock, song thrush, and four types of warbler. The nightingale and woodcock have completely disappeared. All these species nest in low vegetation like bramble.
Meanwhile, the chaffinch, great tit, and mistle thrush, which nest high up in trees, have shown no marked decline.
"Wytham Wood had a very high fallow deer density and it was almost a wipeout," said Hugh Rose of the British Deer Society. "There are very few species of woodland plant that aren't palatable to deer."
The British Deer Society was brought in a few years ago to help manage the fallow deer through controlled culling. Numbers have since been reduced from 75 per 100 hectares of woodland to a single figure density.
"The deer are now down to manageable levels and the wood is already showing some signs of regeneration," added Rose.
Conservation charities are now having to face up to the idea that deer need to be shot if other wildlife is to survive. This measure is unpopular with many of their members.
"It's a delicate matter but people have to realize that deer culling is a fact of life," said Rob Fuller. "We're not talking about elimination, just whether high deer densities are sustainable in terms of maintaining a diversity of wildlife."
The RSPB decided deer culling was the only way to help save the capercaillie at its Abernethy reserve in Scotland. The world's largest grouse, less than 1,000 are left in Britain, making it the country's most endangered bird.
Red deer were severely damaging the native Caledonian pinewood where the birds live. Wire fencing had been used to keep the deer out but this backfired when capercaillies killed themselves by flying into it. The fencing was removed and the resident deer herd cut from 900 to 300. The pinewood began to regenerate and the capercaillie are now coming back from the brink of extinction.
While low-level browsing can be beneficial, by maintaining woodland rides and glades for instance, Hugh Rose says the challenge for landowners and conservationists is to create the right balance between deer and other wildlife.
"It's good land management to control deer because there are no bears, wolves, or cougars to do it for you," he said.
"The British Deer Society is a humane animal welfare organization so it may sound a bit odd that we are advocating deer should be shot. I hear people say, 'This is a nature reserve and we don't like killing things'. I say, 'You won't have a nature reserve much longer if you don't get the deer managed,'" Rose said.
In future, warmer climatic conditions and spreading tree cover due to woodland creation schemes are set to fuel further deer increases. Britain faces a stark choice: Bambi or the birds.
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