|
|
Early Birds: Is Warming Changing U.K. Breeding Season? |
|
James Owen in England for National Geographic News |
| June 3, 2003 |
|
For a bird, the bleak midwinter wouldn't seem an ideal time to go about the precarious business of starting a family. But recent winters haven't been particularly bleak in Britain, and last Christmas scores of fluffy owlets grew fat on mice, voles, and baby rats caught by parents that spotted a breeding opportunity too good to ignore. Scientists at the British Trust for Ornithology (BTO) say 2002's mild temperatures and an explosion in rodent numbers sparked an unseasonal baby boom in the country's barn and tawny owl populations. "We had five cases of tawny owls laying eggs from Christmas week right through to the end of January," said David Glue, a research biologist with the bird conservation charity. "This is exceptional—usually they don't start nesting until the second or third week in March." Glue says the latest in a series of warm years—2002 was the fourth hottest in Britain since records began in 1659, with five of the six warmest occurring since 1990—contributed to a huge increase in the rodents that owls prey on. "An early spring and a late autumn produced a heavy crop of beech mast, hazelnuts, conifer seeds, and other natural fruits, so we had large numbers of voles, mice, and young brown rats," said Glue. Biologists estimate that two billion field voles were born in Britain last year. The usual figure is around 700 million. The barn owl—a ghostly presence at dusk when it hunts on pale, silent wings—also benefited. Glue added: "Many barn owls laid two weeks early during the mild spring which meant 10 percent of them went on to have seconds broods, some as late as December." They included a pair in Cambridgeshire in eastern England which produced a second brood of nine owlets. Fledging successfully just before Christmas, it's the largest second brood ever recorded in British barn owls. Winter Nesting Until recently, winter nesting in British birds has been very rare beyond a handful of species that include the wood pigeon, feral pigeon, and collared dove. There are also cases of certain songbirds kicking off their breeding season before the arrival of spring. Yet ornithologists believe such behavior is becoming an increasingly common phenomenon. Glue said: "We can expect earlier and earlier egg laying and cases of birds nesting right through the winter. This is a reflection of climate change through global warming. "Usually it's increasing day length that triggers egg laying, but if you get exceptional spells of warmth, along with an unseasonal superabundance of food, this can override day length as the main factor." This is also the conclusion drawn from data provided through the BTO's Nest Record Scheme. The largest scheme of its type in the world, it holds over 1.2 million individual nest histories for British birds since 1939. Some 30,000 new records are provided by volunteers each year. "The Nest Record Scheme has provided one of the clearest indications to date of the impact of climate change on British wildlife," said Humphrey Crick, the BTO's senior ecologist. "About a third of the 60-odd species we've looked at show statistically significant trends towards earlier egg laying. This is strong information because it comes from all over the country and isn't restricted to just one study site." Crick says that birds are laying between one and three weeks earlier than they did 15 years ago. For species like the barn owl, which can produce a second brood, this will almost certainly prove advantageous. "For barn owls, the lack of severe winters plus earlier springs are obviously a good thing," said Crick. "It will allow them to fit in more second broods than they normally do." But Crick says for some birds milder conditions aren't so helpful. Great Tit He said: "A single-brood bird like the great tit only has one shot at breeding as they depend on a big splurge of a particular type of caterpillar. Although both the eggs and the caterpillars are appearing a week or so earlier, the trouble is that in favorable conditions caterpillars are able to halve their developmental time from 50 to 25 days. Meanwhile great tits are stuck at about an 18-day incubation period. So if the chicks are a bit late they can hatch after the caterpillars have already disappeared." Changing weather patterns are also influencing Britain's bird life in other ways, for instance by turning rare migrants into breeding residents. Since the 1990s both little egrets and Mediterranean gulls have established colonies after arriving from southern Europe. And last year a pair of European bee-eaters caused a stir when breeding successfully in England for the first time in almost 50 years. The birds, which are hard to miss with their kaleidoscopic plumage, aren't normally found farther north than southern France. "There are other species waiting in the wings to come across from mainland Europe," said Crick. "They include the black woodpecker and fan-tailed warbler which have reached the English Channel. It's a very interesting time to be a bird-watcher." On the other hand, species like the dotterel and snow bunting look set to head northwards, leaving British shores for colder climes. It may be an interesting time to be a bird-watcher in Britain, but they will have to think about investing in a new bird book. Current editions may soon be out of date. More Bird Stories by National Geographic News: Farmers, Conservationists Seek Return of Barn Owls Smell May Play Role in Bird Courtship, Study Finds Bird Teams Flock to Iraq to Survey War's Impact Mystery Disease Stalking Vultures in Asia Humans Are Driving Birds to Extinction, Group Warns Loons Sound Alarm on Mercury Contamination Tall As a Deer, Huge U.K. Bird Staging a Comeback Memory Aids Birds in Migration, Study Finds Crows Better at Tool Building Than Chimps, Study Says Extinction Near for Albatross, Experts Warn 51-Year-Old Albatross Breaks N. American Age Record Are Flashy Male Birds Threats to Their Own Species? Wild and Escaped Parakeets Captivating City Dwellers Bright Beaks Signal Health to Female Birds, Study Says Coot Birds Can Count, Study Says Falconry Used to Secure North American Airports Recent "Birder's Journal" Stories from Robert Winkler: Birder's Journal: Giving Thanks for Wild Turkey Sightings Birder's Journal: Ghost Town's Curse Haunts New England Forest Birder's Journal: Looking at a Handy New Guide Birder's Journal: Learning to Let Birds Come to You Birder's Journal: A Morning With Migrants Birder's Journal: This Warbler Is a Master of Deception Birder's Journal: Seduced by Dueling Thrushes Birder's Journal: Attack of the Flying Goshawk Nationalgeographic.com Bird-Watching Sites: Boston Area Chicago Area Florida Keys Area Maine's Acadia National Park Mount Rainier New Orleans Area New York City Area North Carolina's Outer Banks Philadelphia Area Portland Area Rocky Mountain National Park Salt Lake City Area San Francisco Area Santa Fe Area South Dakota's Black Hills Utah Washington's Olympic National Park Wyoming's Grand Teton National Park Yellowstone National Park Yosemite National Park From the National Geographic Store: Guide to North American Birds Portable Birdsong Identifier Birder's Journal Songbirds Puzzle Additional Information from Related Web Sites: American Bird Center American Bird Conservancy Fish and Wildlife Service Bird Web Site National Audubon Society Environmental Protection Agency: Bird Conservation |
| © 1996-2008 National Geographic Society. All rights reserved. |