AUGUST 2006

The barn swallow performs long migrations

Birds that migrate long distances have adapted to the world's changing climate in unexpected ways, a study shows.

As the planet warms, and spring arrives earlier in Europe, birds are being forced to change their migration patterns.

It had been thought that birds travelling long distances from Africa to Europe would be unable to adapt.

But a study in Science suggests they have evolved in response to climate change and are returning earlier.

The need for migratory birds to time their arrival at breeding grounds with plentiful food supplies is a known evolutionary pressure.

Scientists had assumed that birds travelling short distances would be better able to adapt - and arrive earlier for spring - because of similar climate conditions in their nearby winter grounds. But researchers in Europe decided to test this theory, using long-term banding and observational data from Scandinavia and Italy dating back to 1980. The study revealed that long-distance fliers have adjusted their migration habits to arrive earlier in northern Europe in time for the start of spring.

This suggests a more permanent change in migratory behaviour due to climate change than previously thought.

'Surprising' response

Study-co-author Nils Christian Stenseth, from the University of Oslo in Norway, said migration in the species studied was thought to be a biological response triggered by day length, and not climate variations, in breeding grounds.

"Long-migrating birds arrive at least as early as short-migrating birds," he told the BBC News website. "The trigger is probably related to the length of day, or the photoperiod. "Birds typically respond to the right photoperiod for bringing up as good offspring as possible." The birds begin to reproduce at just one year of age and so have the potential for a rapid genetic response to recent environmental events. They are showing a "surprising and interesting evolutionary response to climate change", he added.

The research is the latest in a string of studies looking at the widespread effects of climate change on birds.

Dr Paul Donald, senior research biologist at the Royal Society for the Protection of Birds, UK, said populations of long-distance migrants breeding in the UK and across Europe were showing worrying declines.

"This study highlights the potential role climate change is playing," he said. "However, we must not ignore other potential factors affecting their fortunes here in the UK or on their wintering grounds in Africa."

Migratory birds have suffered a dramatic decline in numbers, according to a study.

Species that migrate thousands of miles from Africa to the UK have been the worst hit over the last 30 years.

The researchers say the cause of the decline remains a "mystery", but could be linked to climate change, habitat destruction or pesticide use.

Writing in the journal Biological Conservation, they warn the losses may indicate wider environmental damage.

The Royal Society for the Protection of Birds (RSPB) and BirdLife International study analysed population trends of European breeding birds, including non-migratory birds and those that migrate both short and long distances.

The data spanned three decades, from 1970 to 2000.

"We found that long distant migrants - the ones that go right across the Sahara, like the swallows, flycatchers and warblers - have shown a fairly consistent pattern of decline," said Dr Paul Donald, an author on the paper from the RSPB.

Those that winter in Africa, he said, seem to be the most affected.

The study also compared the long-distant migratory birds with closely related non-migratory birds, but again found in almost every case that the migratory birds faired worse.

The roller has suffered dramatic losses

Fifty-four percent of the 121 long-distant migratory birds studied suffered plummeting numbers or had even become extinct since 1970.

The roll-call of declining species is long.

"Some fairly iconic species have declined enormously in Europe. There is a very beautiful blue and purple bird called the roller - the population of that bird is crashing all over Eastern Europe," Dr Donald told the BBC News website. "In the UK, other species that have declined enormously are spotted flycatchers, pied flycatchers, wheatears, wood warblers and tree pipits."

Changing climate

The exact reason for the birds' decline, according to the authors, is a "mystery". But several theories to explain the losses have been put forward, and will now be investigated. One explanation is tied to the changing conditions in Africa, where the birds winter.

"We know that agriculture has spread; we know there has been a long-term drought in the Sahel; and we know huge amounts of pesticides are used to control locust outbreaks," said Dr Donald.

The wryneck no longer breeds in the UK

The swelling size of the Sahara may also be hampering the birds. Migrating birds face longer and longer non-stop flights across the desert.

Climate change has been highlighted as a potential culprit. Warmer springs in Europe are causing some insects to hatch earlier in the year, which means by the time the migratory birds arrive to breed and raise their young they may have missed their much-needed food-source. "Migrants make up a high proportion of our species of birds, so this is a big conservation issue," said Dr Donald. "But if you think that these are birds that cover vast areas of the Earth's land-surface - this consistent pattern of decline is indicative that there are some pretty severe environmental changes going on somewhere which might also have an impact on humans."

The authors conclude that urgent action is needed to uncover the cause of the decline. "There is something about being a migrant that counts against them," said Dr Donald. "These birds have been slipping away from under our noses for 30 years, and we've never has really noticed it before."

Bird Extinction Estimates May Be Too Low

Since 1500, more than 150 bird species have disappeared from the world, including the much lamented dodo. This ground bird disappeared from its island home before Carl Linnaeus, the father of scientific taxonomy, even described it in the 18th century. Given that many of the nearly 10,000 known bird species have only recently been described--including those only available from remains like the dodo--some biologists suggest that current extinction rates have been seriously underestimated and will rise rapidly in the coming century.

Stuart Pimm of Duke University and his colleagues analyzed current estimates of bird extinction rates. Out of 9,975 known bird species, 154 have disappeared, or roughly 1.3 percent. Extrapolated, this yields an estimate of 26 extinctions per million bird species every year. Based on fossil records, scientists estimate that normal extinction rates average just one lost animal for every million species per year. But the researchers argue that the estimate of human impact on birds fails to account for new species identified from remains and those species likely to be extinct but not yet declared so in order to continue conservation efforts. Such efforts have had a demonstrable impact, dropping the extinction rate by half over the course of the last century. "Were it not for conservation actions, there would have been these 25 prevented extinctions plus the actual 20 extinctions in the wild over the last 30 years," the scientists write in a paper published online this week in Proceedings of the National Academy of Sciences.

Conservation, however, will not be enough to save many of the bird species most at risk. Habitat destruction partnered with climate change, which particularly impacts those birds lingering at the edges of their ranges, will eventually doom 1,700 species of birds, boosting extinction rates to roughly 1,000 out of one million species every year. "Millions of people are fond of birds," the authors note. "Whether fondness will prove sufficient to protect the thousand or more species threatened with habitat loss across tropical forests remains to be seen. Even if it does, this fondness for birds is not likely to protect completely the remainder of biodiversity." --David Biello

A change in the diet of seabirds may be making them less intelligent and lowering their chances of survival and breeding, a new study shows.

Scientists used lab experiments to mimic changes observed in the diets of kittiwakes in the Bering Sea - changes probably caused by a warming ocean.

Chicks given a diet low in lipid-rich fish were less able to find food.

The RSPB comments that changes in the diets of seabird chicks can affect their chances of survival.

The 1980s saw the start of a decline in populations of red-legged kittiwakes on the Pribilof Islands in the south-eastern Bering Sea, off the coast of Alaska.

Numbers roughly halved over two decades.

The cause has been unclear, though scientists have documented a change in their diet which occurred around the same time.

"With many of the top predators - sea lions, birds - people were talking about drastic population declines," said Alexander Kitaysky from the University of Alaska, one of the scientists on the current study.

"Ecosystems started to change; one of the most pronounced changes was that high-lipid fish such as capelin declined, and were replaced in the kittiwake diet by species such as juvenile pollock which are poor in lipids," he told the BBC News website.

Lab food

Young kittiwakes learned to associate couloured lids with food

The cause of this dietary adjustment may be related to climate change, with rising temperatures documented in the Bering Sea at that period perhaps driving the movements of fish populations.

To investigate what impact a forced switch to a low-lipid regime might have on the development of red-legged kittiwakes, the Kitaysky lab designed experiments to explore the effects of various diets. Twenty kittiwake chicks were hatched in captivity and assigned randomly to four fish diets: high-volume high-lipid, high-volume low-lipid, low-volume high-lipid, and low-volume low-lipid. At the age of 47 days, the birds began learning to associate food with containers having lids of various colours. Those which had been fed a high-lipid diet learned quickly and remembered which containers to go for; those on a low-lipid regime did not learn to discriminate between the various colours.

Alexander Kitaysky believes that in the wild, such an impairment to learn would prove crucial to a bird's survival and its ability to breed and rear offspring. "Always their food is associated with some signs on the surface or the ocean, whether a change in colour or foam," he said, "and they're supposed to memorise the association. "Most of these chicks would not make it through their first year."

Lipids are believed to boost the mental development of mammals, including humans; other work in the Kitaysky lab suggests that chicks deprived of lipids show increased levels of stress hormones, which could be behind their mental impairment.

Size matters too

Red-legged kiitiwakes resting on the Pribilof Islands

Norman Ratcliffe, a seabird biologist for the British-based Royal Society for the Protection of Birds (RSPB), said that mental impairment might not be the only mechanism by which a poor diet in infancy affects a bird's foraging ability and survival. "This study shows that chick nutrition can affect the ability of birds to find food after they fledge in artificial situations," he told the BBC News website. "However, whether this has contributed to the decline of red-legged kittiwakes in the wild is unclear; the study shows that chicks fed poor quality diets are lighter as well as cognitively impaired, and this could also lower their chances of post-fledging survival."

Around the coast of the UK, some sea bird populations are in catastrophic decline, also due largely to the removal of high-lipid prey such as sand eels. This appears also to be linked with climate change If anything, they are worse off than the Pribilof kittiwakes, as it appears that the disappearing sand eels are not being replaced by any other species.

The Kitaysky study is reported in the Royal Society's science journal Proceedings B.

Wildlife experts say the two consecutive dry winters are beginning to have an impact on flora and fauna in parts of the UK affected by drought conditions.

The RSPB says 2006 is one the worst breeding seasons on record for wetland birds. Rainfall in England and Wales over the past 18 months has been the second lowest since 1976, but water levels in parts of central and southern England are at their lowest level since the 1930s. "If you have a dry winter like the one we have had then you are not able to make the wetlands suitable for the birds you are trying to attract," says Phil Burston, the RSPB's senior water policy officer. He said fewer birds such as lapwings, redshanks and snipes have arrived at the charity's wetlands reserves.

"Our reserve at Elmley Marshes in Kent would, in a normal year, have about 200 pairs of lapwings. Last year it had 80 pairs, and this year it looks as if we have just 60 pairs. So the trend is downwards."

Mr Burston says that a number of birds that did arrive have made no attempt to nest because conditions are too dry. He says although the breeding season closes towards the end of June, a dry summer will make matters worse. "The adults and the young have to find food, such as invertebrates in moist soils. So if these wetlands dry up then the waders will not be able to get access to their food. If that continues, they will eventually die."

To help alleviate the problem, the RSPB has been granted a 28-day licence by the Environment Agency to pump water from a nearby creek on to the marsh.

Shifts in spring temperatures in central Europe may be having a significant effect on the ability of birds to breed successfully, say scientists.

While the full impact of climate change is not yet clear, some birds whose populations rely on hatching two clutches of eggs a year may be hit hard.

The research, covering two decades of data and published in a journal of the Royal Society, looked at populations of great tits (Parus major) and blue tits (Parus caeruleus)

However, the researchers said that these species were representative of many other common European birds. The breeding behaviour of tits varies throughout Europe, with some populations producing just one clutch of eggs in spring and others managing two.

Food shortage

Obviously, the birds choose spring because it is the time of year with an abundance of suitable food - in this case caterpillars and suchlike. However, a warmer spring hastens the development of the caterpillars, meaning there is a shorter period before they become butterflies or moths. This means there may be insufficient food to support two broods in a single spring.

The researchers found that in areas in which "double-brooding" was commonplace, the move was towards single brooding. And in areas in which birds only produced one brood, the timing of egg-laying tended to be earlier. This, said the researchers, was clear evidence that climate change was having an impact.

Wait and see

Dr Marcel Visser, from the Netherlands Institute of Ecology, said many factors would influence whether there would be an adverse impact on bird populations over time. However, he said it was likely that a move from "double-brooding" to single clutches would not be beneficial. He told BBC News Online: "Climate change is changing all these populations of birds.

"Obviously, the warmer winters might mean that more of the birds are likely to survive through the winter. "What we are trying to find out now is whether these birds are likely to adapt to the changes."

John Lanchberry, head of climate change at the RSPB, told BBC News Online that he would expect to see more opportunistic species moving into new areas further north. However, he added: "They can only do this if the food is there for them to eat. The danger is if different species move at different rates - you could end up with a different ecosystem."

Bees and flowers decline in step
By Richard Black
Environment correspondent, BBC News website

Diversity in bees and wild flowers is declining together, at least in Britain and the Netherlands, research shows.

Scientists from the two countries examined records kept by enthusiasts dating back more than a century.

They write in the journal Science that habitat alterations, climate change and modern industrial farming are possible factors in the linked decline.

There is a chance, they say, that the decline in pollinating bees could have detrimental effects on food production.

"The economic value of pollination worldwide is thought to be between £20m and £50m ($37m and $91m) each year," said Simon Potts from the University of Reading, UK, one of the scientists involved.

While declines in Britain and the Netherlands might not indicate a global trend, the team says, it is an issue deserving serious future research.

Costs of specialism

Study leader Koos Biesmeijer from the UK's University of Leeds is not the first biologist to note the value of amateur enthusiasts to British conservation studies, and will not be the last.

"We have relied here on records kept by enthusiasts; just like bird-watchers keep records of bird-sightings, they keep records of bees and hoverflies and plants," he told the BBC News website.

"In the UK, insect records come from the Bees, Wasps and Ants Recording Society (BWars) and the Hoverfly Recording Scheme (HRS), while in Holland the Dutch Entomological Society does something similar.

The ultimate drivers are changes in our landscapes; intensive agriculture, extensive use of pesticides, drainage, nitrogen deposition Koos Biesmeijer

"The records go back even into the last part of the 19th Century, and then some of these enthusiasts have gone back into the scientific literature and verfied records."

From these records comes a picture of reducing diversity among bees and wild flowering plants.

Bee species which rely on certain plants, and plants which rely on certain bees, have fared worse; more flexible species of both have done better.

In Britain, bee species which have increased since 1980 are those which were already common before.

The researchers also looked at hoverflies, and found a mixed picture, with diversity remaining roughly constant in Britain but appearing to increase marginally in the Netherlands.

Hoverflies do pollinate plants, but are less choosy than many bee species, and do not depend so directly on nectar to feed their young.

Overall, plants which pollinate via wind or water appear to be spreading, while those which rely on insects decline.

Holistic handling

If the diversity of bees and plants is decreasing, one question is: which declined first?

This study cannot provide an answer, though it appears the fates of both are intertwined; but the root causes of the decline are clear, Dr Biesmeijer argues.

"The ultimate drivers are changes in our landscapes; intensive agriculture, extensive use of pesticides, drainage, nitrogen deposition.

"All of these factors favour subsets of plants and subsets of bees.

"And if you want to prevent them you have to look at the ecosystem level, protecting the habitat and the groups of species."

Where habitats have been restored, for example under agro-environment schemes, bee and plant diversity has sometimes started to re-emerge, he said.

While such changes may have significant impacts nationally, the team points out that the environments of Britain and the Netherlands, with their high population densities and long histories of agriculture, contain two of the least "natural" landscapes on Earth.

Other countries, with a greater proportion of natural habitat, may not show the same declining trend, they say; but given the importance of bees for pollination, they suggest it would be worth finding out.

Richard.Black-INTERNET@bbc.co.uk