Migratory birds can be taught to adjust to climate change

One result of climate change is that spring is arriving earlier. However, migratory birds are not keeping up with these developments and arrive too late for the peak in food availability when it is time for breeding. By getting the birds to fly a little further north, researchers in Lund, Sweden, and the Netherlands have observed that these birds can give their chicks a better start in life.

Global warming is causing problems for birds in Sweden and elsewhere. Warmer springs mean that caterpillars hatch, grow and pupate earlier compared with just a few decades ago. This has consequences for birds that cannot eat caterpillars that have entered the pupal stage. Therefore, when the food supply runs out at an ever earlier time in the spring, more and more chicks starve during the breeding season. This is a big problem for migratory birds that spend winters in Africa, as they do not know how early spring arrives in Sweden. Could the problem be solved if the migratory birds simply came home and started breeding earlier?

"It seems that our non-migratory birds are doing this to a certain extent. But, of course, they are present and can feel how early spring will come. We thought that perhaps the migratory birds could fly further north until they find a place with suitable well-developed caterpillars," says Jan-Åke Nilsson, biology researcher at Lund University in Sweden.

To test this in practice, the researchers decided to help some Pied Flycatchers along the way. The biologists caught Pied Flycatchers that had arrived prior to breeding in the Netherlands. The birds were then driven during the night to Vombs Fure, an area of pine forest outside Lund in Skåne, where they were released. The peak of caterpillar availability in Skåne is about two weeks later than in the Netherlands -- a distance of around 600 kilometres that a Pied Flycatcher could cover in just two nights.

"The birds that were given a lift from the Netherlands to Skåne synchronised very well with the food peak! As they started to breed about 10 days earlier the "Swedish" Pied Flycatchers they had a dramatically better breeding success than the Swedish ones as well as a better success than the Pied Flycatchers that remained in the Netherlands," says Jan-Åke Nilsson.

In addition, it was shown that the chicks of the Dutch Pied Flycatchers that had received migration assistance did not stop in the Netherlands when they returned after their first spring migration. Instead, they continued on to the area of pine forest outside Lund where they were born. Furthermore, they arrived earlier than the Swedish Pied Flycatchers and thereby had more well-fed chicks at Vombs Fure the year after the researchers gave the Pied Flycatchers a helping hand to find Skåne.

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To know where the birds are going, researchers turn to citizen science and machine learning

Computer scientists at the University of Massachusetts Amherst, in collaboration with biologists at the Cornell Lab of Ornithology, recently announced in the journal Methods in Ecology and Evolution a new, predictive model that is capable of accurately forecasting where a migratory bird will go next -- one of the most difficult tasks in biology. The model is called BirdFlow, and while it is still being perfected, it should be available to scientists within the year and will eventually make its way to the general public.

"Humans have been trying to figure out bird migration for a really long time," says Dan Sheldon, professor of information and computer sciences at UMass Amherst, the paper's senior author and a passionate amateur birder. "But," adds Miguel Fuentes, the paper's lead author and graduate student in computer science at UMass Amherst, "it's incredibly difficult to get precise, real-time information on which birds are where, let alone where, exactly, they are going."

There have been many efforts, both previous and ongoing, to tag and track individual birds, which have yielded invaluable insights. But it's difficult to physically tag birds in large enough numbers -- not to mention the expense of such an undertaking -- to form a complete enough picture to predict bird movements. "It's really hard to understand how an entire species moves across the continent with tracking approaches," says Sheldon, "because they tell you the routes that some birds caught in specific locations followed, but not how birds in completely different locations might move."

In recent years, there's been an explosion in the number of citizen scientists who monitor and report sightings of migratory birds. Birders around the world contribute more than 200 million annual bird sightings through eBird, a project managed by the Cornell Lab of Ornithology and international partners. It's one of the largest biodiversity-related science projects in existence and has hundreds of thousands of users, facilitating state-of-the-art species distribution modeling through the Lab's eBird Status & Trends project. "eBird data is amazing because it shows where birds of a given species are every week across their entire range," says Sheldon, "but it doesn't track individuals, so we need to infer what routes individual birds follow to best explain the species-level patterns."

BirdFlow draws on eBird's Status & Trends database and its estimates of relative bird abundance and then runs that information through a probabilistic machine-learning model. This model is tuned with real-time GPS and satellite tracking data so that it can "learn" to predict where individual birds will move next as they migrate.

The researchers tested BirdFlow on 11 species of North American birds -- including the American Woodcock, Wood Thrush and Swainson's Hawk -- and found that not only did BirdFlow outperform other models for tracking bird migration, it can accurately predict migration flows without the real-time GPS and satellite tracking data, which makes BirdFlow a valuable tool for tracking species that may literally fly under the radar.

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