Human Feeding Creates New Population of Birds

Charles Q. Choi, LiveScience.com Yahoo News 3 Dec 09;

By feeding birds, you could alter their evolutionary future, with changes visible in the very near term, scientists now conclude.

Due to winter bird-feeding, what was once a single population of birds has, in fewer than 30 generations, been split into two groups that do not interbreed, despite the fact that they continue to breed side by side in the very same forests.

"Our study documents the profound impact of human activities on the evolutionary trajectories of species," said researcher Martin Schaefer, an evolutionary biologist at the University of Freiburg in Germany. "It shows that we are influencing the fate not only of rare and endangered species, but also of the common ones that surround our daily lives."

Wings of change

Over the course of three-and-a-half years, the scientists followed birds known as blackcaps (Sylvia atricapilla) in Central Europe after humans began offering food to them. A recent divide has sprung up, with two groups following distinct migration routes in the winter - one southwest in Spain, the other northwest in the United Kingdom.

"The new northwest migratory route is shorter, and those birds feed on food provided by humans instead of fruits as the birds that migrate southwest do," Schaefer said. "As a consequence, birds migrating northwest have rounder wings, which provide better maneuverability but make them less suited for long-distance migration." They also have longer, narrower bills that are less equipped for eating large fruits like olives during the winter.

This discovery, detailed online Dec. 3 in the journal Current Biology, speaks to a long-standing debate in evolution about whether geographic separation is necessary for new species to develop. By now, the level of reproductive isolation between these populations, which live together for part of the year, is now stronger than that of other blackcaps that are always separated from one another by distances of 500 miles (800 km) or more.

"This is a nice example of the speed of evolution," Schaefer said. "It is something that we can see with our own eyes if we only look closely enough. It doesn't have to take millions of years."

If such isolation and differentiation continues, they can ultimately become separate species.

"The initial steps in speciation - that is, the evolution of reproductive isolation, have rarely been studied," Schaefer said. "This is because speciation is necessarily a historic process, and it is extremely difficult to analyze the selective pressures that lead to speciation in hindsight. Here, we can witness those initial steps."

Other species affected

Schaefer doubts these groups of birds will become different species, because the habits of humans will tend to change over time. Still, he expects humanity will continue to influence the evolution of common species.

"For example, introducing honeybees for securing pollination in crop species has the potential to influence plant-pollinator interactions," Schaefer said. "Plants might adapt to the relative lower importance of native pollinators and change to a more generalistic floral design that could be more efficiently exploited by honeybees."

When it comes to the evolutionary potential of species to adapt to modern impacts on the environment, such as ones caused by climate change, "We know that many of the species are likely unable to adapt quickly to such changes," Schaefer said. "However, I think that the blackcap provides a good example that some species are able to adapt quickly to contemporary ecological changes. This, I believe, is an important and positive result in the current debate, although I need to caution that we cannot extrapolate it easily to other species."

Feeding birds 'changes evolution'
Victoria Gill, BBC News 3 Dec 09;

Bird-feeders, hung in many a garden, can affect the way our feathered friends evolve, say scientists.

European birds called blackcaps follow a different "evolutionary path" if they spend the winter eating food put out for them in UK gardens.

The birds' natural wintering ground is southern Spain, where they feed on the fruits that grow there.

Researchers describe the impact this well-intentioned activity has had on the birds in Current Biology journal.

Dr Martin Schaefer from the University of Freiburg in Germany led the research.

He and his team found that blackcaps that migrated to the UK for the winter were in the very earliest stages of forming a new species.

He explained that some blackcaps ( Sylvia areicapilla ) would always have migrated "a little further north" than others and eventually "ended up in Britain in the winter".

"But those birds would have had nothing to eat," he said.

It was when garden bird feeders became more popular in the UK, that an evolutionary division began to emerge.

"As soon as the British provided a lot of bird food, those birds would have had a much higher probability of surviving the winter."

And because the UK is closer to their breeding ground, those birds would also have returned earlier to claim the best territory.

The researchers, from Germany and Canada, set out to discover if the birds that spent the winter availing themselves of garden bird-feeders were in fact a distinct group.

To do this, they studied the blackcaps at a breeding ground in Germany.

The team were able to use a chemical "signature" from the birds' claws to identify where they spent the winter, and what food they ate.

"Then we took blood samples and analysed those to assess whether... we had two distinct populations. And that's exactly what we found," said Dr Schaefer.

"To a very large extent the birds only mate [with] birds with the same overwintering grounds as them."

This initial "reproductive isolation", Dr Schaefer explained, is the very first step in the evolution of a new species.

"This tells us that by feeding birds in winter we... produce an evolutionary split. And we have produced these initial steps in as little as 50 years."

The team also observed differences in the birds' beaks, wings and plumage.

Blackcaps that migrated along the shorter route to the UK had rounder wings, and longer, narrower beaks.

The scientists said these differences were evidence that the birds had adapted to their shorter journey, and to eating seeds and fat from bird-feeders, rather than fruit from shrubs and trees.

But, Dr Schaefer pointed out that the evolution of a new bird species "could take 100,000 to a million years".

"At this stage this is reversible," he added. "And it's hard to envision a species change, because if there's another economic crisis and people stop feeding the birds, the whole system might just collapse."

Man-made change

In this case, Dr Schaefer thinks the human impact on blackcaps has been a positive thing.

"[The birds have] found a better overwintering area that is closer to the breeding ground, where they can obtain food easily.

"And I also think its positive news for us, because it means not all the changes we produce are necessarily bad, and that some species have the potential to adapt quickly to the changes."

Grahame Madge from the Royal Society for the Protection of Birds (RSPB) said that this was "a fascinating piece of research" and that it fitted in with the birds adapting to a changing climate.

"Blackcaps have been able to start this behaviour because of the milder winter we've experienced in the last few decades," he said.

"And because they're getting food, this reinforces the behaviour and will enable them to survive a colder winter [in the UK]."

He added that putting food out for birds in the winter was "very important" and that many birds "need the energy boost at this time of year".