News for March 2001
Bird On! News
1st March 2001
Can birds spread foot and mouth disease? This is one of the questions that no one has answered satisfactorily, but which becomes horribly pertinent while the present outbreak of this dreaded disease sweeps across Britain. During the last major outbreak, in 1967, a number of farmers suggested that pied wagtails might be responsible for carrying the virus, for pied wagtails are the most characteristic of farmyard birds. Pied wagtails certainly do fly from one farmyard to another, but whether they can carry the foot and mouth virus remains unproven.
We do know that foot and mouth virus is remarkably mobile, and can be carried on the wind, so there has to be a possibility that birds can carry it. Other farmland birds must also come under suspicion, particularly gulls that move so freely from one pasture to another. If birds can spread the disease, then such precautionary efforts as putting disinfected straw at farm gates seem somewhat futile.
Farming was an industry in crisis before the outbreak of foot and mouth: the impact of the disease is sure to see many livestock farmers go bankrupt, and many others to give up livestock altogether. However, what many people forget is that livestock farming provides essential habitat for many birds that feed or live on farmland. The flocks of barnacle geese from Greenland that winter on the Scottish island of Islay, for example, favour pastures grazed short by cattle and sheep, and part of the RSPB's management of its reserve on Islay is to graze its pastures with livestock to get the sward to the length the geese prefer.
Essential habitatFor waders such as snipe and redshank that nest on lowland marshes, grazing is essential, as it creates the habitat they require. As soon as these damp pastures are converted to arable, usually to grow winter cereals, the nesting birds disappear. It's not just waders and wildfowl that require livestock grazing for their habitat, so, too, does our rarest crow, the chough. This attractive red-legged and red-beaked bird likes close-cropped pastures where it can probe for the insects that make up the major part of its diet.
Though agriculture is the primary rural land use, a high percentage of farmland in Britain is also used for shooting, chiefly of pheasants and partridges. Modern farms provide relatively little natural cover for gamebirds, so shoot managers are often forced to sow cover crops for their game. Research by the British Trust for Ornithology's Habitats Department has shown the increasing value of these cover crops to songbirds.
A number of different game-cover crops are planted in Britain, including kale, quinoa, maize, millet, mustard, sunflowers, buckwheat and canary grass. The BTO's study showed that with the exception of skylarks and grey partridges, the densities of all birds seen on farmland were higher on winter cover crops than they were in nearby conventional crops, such as cereals or rape.
However, individual species showed marked preferences. Mustard, for example, was strongly preferred by goldfinches , chaffinches and greenfinches , but otherwise was one of the least popular crops. Sunflowers, a popular game cover crop, were most popular with greenfinches, and to a lesser extent yellowhammers and chaffinches, but few other species were attracted to them in significant numbers. I wonder whether this lack of popularity of sunflowers was a reflection of the time of the year when the BTO survey was undertaken, as early in the season (October) I have seen sunflower crops crowded with a variety of species, including tits. The seeds soon spill and get eaten, so the popularity of the crop declines sharply.
What the BTO survey did find was that kale is much the most popular crop. In its second year it attracts birds in abundance and variety, including finches, buntings and tree sparrows, as well as insectivorous passerines such as blackbird , song thrush and dunnock that forage below the leaves for invertebrates and small seeds.
Ian Henderson and Juliet Vickery, writing about the survey in the January-February BTO News, note that "purists will perhaps regard winter bird crops as little more than a glorified bird table, but abundant winter bird food is a critical resource that is currently missing from the farmland ecosystem". Whatever ones views about the moral rights and wrongs of the sport of shooting, the BTO's research shows that shooting estates provide valuable food and habitat for many farmland species.
Declining farmland birdsAnother BTO report, discussed in the same issue of BTO News, confirms that many species of farmland birds have suffered serious declines during the last 25 years. Grey partridges, for example, are down by 83%, and only corn buntings (86%), tree sparrows (94%) and lesser redpolls (also 94%) have suffered worse. These figures come from information from several long-running BTO surveys, including the BBS (Breeding Bird Survey), CBC (Common Bird Census), WBS (Water Bird Survey).
The collapse in the grey partridge population seems likely to lead to calls for it to be removed from the quarry list. At the moment the grey partridge is classified as a game bird, and can be shot from September 1st until February 1st. However, legislation that removes the grey partridge from the quarry list is unlikely to do the species any good in the long run.
Chris Mead, in his excellent book The State of the Nations' Birds (Whittet Books, 2000), explains that detailed research by the Game Conservancy shows that the partridge's plight is due to the lack of insect food for young chicks because of the intensification of agriculture. He adds "paradoxically the birds are doing well in areas like Norfolk, where they are intensively shot but well looked after. Perhaps they should be taken off the game list on estates where they are not carefully nurtured!"
It is still possible to produce a shootable surplus of wild partridges, but it takes a good deal of hard work and sensitive husbandry. Blanket protection of the partridge would destroy the main incentive to look after this species, and there is no doubt that the result would be disastrous for the partridge's long-term future.
Unfortunately, selective legislation that restricted partridge shooting to certain estates would be impractical. If there is to be any change to the partridge's quarry status, then the only sensible move is to close its season on December 31st. Wild grey partridges pair in early January, and shooting birds that have already paired is sheer folly, comparable with eating your seed corn.
Conservationist can often be accused of dwelling on the bad-news stories, and ignoring the good news. The same BTO report also shows that a number of birds have experienced a considerable increase in numbers during the last 25 years. Sparrowhawks and buzzards , redstarts and nuthatches have all enjoyed increases of more than 100% during this period. However, the prize for the biggest increase goes to the tufted duck , with a massive 645% population rise. It is interesting to note that just a couple of centuries ago, the tufted duck didn't nest in Britain, and was only known as a wintering bird. The first nest was found in Yorkshire in 1849, with a rapid increase apparent from the 1880s. Tufted ducks have benefited from the attractive new habitat provided by gravel pits, while the latest increase shows a growing adaptability to nest on smaller ponds and lakes.
From birds to butterfliesOn March 1st Oxford University Press published the Millennium Atlas of Butterflies of Britain and Ireland. I was one of some 10,000 observers who contributed over 1.6 million butterfly sightings to the Atlas, making it the largest and most detailed survey of butterflies ever carried out. The Atlas itself is a handsomely produced volume, illustrated throughout with exquisite colour photographs.
What the Atlas does show is that half of Britain's butterfly species have declined substantially over the past 200 years. In addition, five have become extinct, and 15 have been lost from over 50% of their range. It is butterflies of woodland and wet meadows that have been worst affected, with the fritillaries hit hardest of all. The high brown fritillary has suffered a 77% decrease since the 1970s, while pearl-bordered and marsh fritillaries have also declined to a worrying degree.
According to Dr Martin Warren, Director of Conservation for the charity Butterfly Conservation (the organisation that is responsible for the new Atlas), "Land use changes over the past 50 years have been disastrous for butterflies as their habitats have been lost to intensive agriculture and forestry. The only way back for butterflies is if farmers, foresters and land owners are supported to manage their land in a more wildlife friendly way."
Fortunately it is not all bad news for butterflies, as no fewer than 15 species have increased their range in Britain. These include the Essex skipper, brown argus, comma and marbled white. All have moved northwards, almost certainly as a result of global warming.
(Details of BTO surveys can be found on the BTO's web site: www.bto.org).