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Ecology & Environmental Sciences - Songbird Superhighway

It was 8:10 on a mild, clear October 2009 morning on Metinic Island in Penobscot Bay, and a group of University of Maine researchers was already several hours into a shift collecting, banding and analyzing songbirds migrating off the Maine coast.

Adrienne Leppold

University of Maine graduate student Adrienne Leppold is one of the country’s foremost bird banders. During the fall and spring migration seasons, she lives on Metinic Island off the Maine coast, conducting research there as part of the Northeast Regional Migration Monitoring Network. Through her research, supported by the U.S. Fish and Wildlife Service Maine Coastal Islands National Wildlife Refuge, Leppold made the important discovery that the island is a major flyway for songbirds.

University of Maine graduate student Adrienne Leppold is one of the country’s foremost bird banders. During the fall and spring migration seasons, she lives on Metinic Island off the Maine coast, conducting research there as part of the Northeast Regional Migration Monitoring Network. Through her research, supported by the U.S. Fish and Wildlife Service Maine Coastal Islands National Wildlife Refuge, Leppold made the important discovery that the island is a major flyway for songbirds.

University of Maine graduate student Adrienne Leppold is one of the country’s foremost bird banders. During the fall and spring migration seasons, she lives on Metinic Island off the Maine coast, conducting research there as part of the Northeast Regional Migration Monitoring Network. Through her research, supported by the U.S. Fish and Wildlife Service Maine Coastal Islands National Wildlife Refuge, Leppold made the important discovery that the island is a major flyway for songbirds.

Rebecca Holberton, one of the nation’s top bird biologists, had arrived several days earlier, joining UMaine graduate student Adrienne Leppold, who oversees banding operations on Metinic and is a key member of Holberton’s Laboratory of Avian Biology. Leppold had already been on the island several weeks, going through a daily routine that included waking up before dawn, setting up nets, capturing birds, taking measurements, and banding the leg of each before release, doing visual surveys of birds landing on the island, and then retreating to a small cabin to analyze data and repeat the process the next day.

That morning, Leppold was busy banding under a tent when Holberton called to her to come outside. Leppold left the tent, looking down as usual to carefully tiptoe through throngs of birds amassed on the ground.

Look up, Holberton told her. What Leppold saw was shocking and thrilling at the same time – multiple flocks each made up of hundreds of birds moving west-southwest over the island. One flock of about 150 yellow-rumped warblers stopped and hovered briefly over the treetops west of the banding tent before splitting, with half the flock coming down to land in the trees and the other half continuing on.

“I could almost feel them thinking. It was a moving experience,” Leppold says, recalling the moment. “Most of these birds are nocturnal migrants, and this was 8:10 a.m. And there was the same insanity on the ground around us. Up until that point I hadn’t noticed such movements, but I also wasn’t really looking, as banding demands on-the-ground attention. I think at that moment was when it hit me that this was something huge.”

Huge, indeed. What Holberton noted visually that morning, and what Leppold was able to substantiate while conducting research on Metinic Island, was that the Gulf of Maine serves as a sort of superhighway for songbirds migrating between Canada and South America. It was a major find not only for Holberton’s lab, but also for an international effort to document the movements of migrating songbirds in the Gulf of Maine.

The Northeast Regional Migration Monitoring Network, a cooperative of Canadian and U.S. nonprofit organizations, government agencies and university researchers such as Holberton and her research team, has spent the last two years trying to determine how migrating species use the Gulf of Maine’s complex network of islands and coastal areas. Using a combination of decades-old monitoring techniques and newer technologies, Network researchers are examining migratory movements made by both large groups of birds and individuals.

“We’re combining techniques and technology for tracking small birds,” Holberton says. “With the monitoring network and the sites all over the Gulf of Maine, we can couple all these approaches across scales.”

In addition to the groundbreaking nature of the findings and combination of research methods, the collaborative nature of the Network itself is unheard of in the world of bird migration research, at least in the Gulf of Maine.

Faculty and student researchers from UMaine and Acadia University in Nova Scotia are involved, along with U.S. Fish & Wildlife Service biologists at the Maine Coastal Islands National Wildlife Refuge, the National Park Service and several established bird banding stations such as the Atlantic Bird Observatory in Nova Scotia, Appledore Island Migration Station in the Isle of Shoals, and Manomet Bird Observatory in Massachusetts.

Network researchers are now collecting data about the species and numbers of birds captured on the migration highway, as well as where they come from and where they’re going. The Network’s ultimate goal, however, isn’t to simply amass information. Scientists are hoping to have as clear of an understanding as possible about the gulf’s migrants because current and emerging issues such as climate change, loss of habitat through development of inland and coastal areas, and alternative energy initiatives along the Maine coast will inevitably affect the mass migrations.

“We’re at the northern end of their spring migration, so of course the birds that we get would be breeding north of us,” says Holberton, who also is part of the ecological monitoring team working on UMaine’s DeepCwind offshore wind power initiative. “Those are the habitats that are really going to be the first and fastest to go in response to global climate change. If we don’t have some idea of what we’ve got now, we won’t have a feeling for how quickly population change is happening. And we certainly don’t want to exacerbate it by increasing mortality or making it more difficult for birds to reach their destinations.”

Although the collaborative nature of the Network is new, bird migration research in the Gulf of Maine has been going on for more than 100 years.

In the 19th century, Holberton says, the U.S. Department of Agriculture was interested in the impact of migratory birds on crops and newly seeded fields sometimes decimated by migrants. USDA created in 1885 the Office of Economic Ornithology and Mammalogy – a forerunner of the current U.S. Fish and Wildlife Service now housed in the Department of the Interior – which tasked lighthouse keepers in the Gulf of Maine with recording their observations about the timing of birds’ arrivals, the types and numbers of birds. In addition to the keepers’ scientific data, their observations became part of the cultural history of the life of a lighthouse keeper. Holberton has the original records, and says the birds became an important and welcome harbinger of spring for many of those in the isolated lighthouses.

“You can imagine being out there all winter and then you start seeing birds land, geese, bluebirds, robins, all this bright color,” she says. “The lighthouse keepers would write that it had been a tough winter, and they were glad to see the birds this year. So there is some interesting information in those notes.”

In England during World War II, as radar developed and its use became widespread, flocks of large migrating birds such as geese were detected and occasionally mistaken for squadrons of enemy planes.

It wasn’t until the 1960s, however, that scientists began basic research into the study of bird movements using surveillance radar in the Gulf of Maine, with studies documenting the directions in which birds were moving and the density of those flocks of birds. Scientists used ceilometers, a powerful light developed to determine the cloud ceiling at airports, to see and count birds as they flew through the beam of light pointed up at the sky.

Those techniques added critical knowledge about movements of flocks of birds on a large, landscape scale, but the researchers are now asking individuals more directly about their preferred direction. During so-called orientation release tests, first used in the Gulf of Maine by one of Holberton’s former graduate students, the researchers capture birds during the day and glue to the birds’ back a small, clear capsule filled with fluid that glows brightly in the dark. The birds are released after dark and their chosen direction is recorded by watching the movement of the capsule, often for up to two miles. The capsule falls off in 3-4 hours, after which time the bird is well on its way.

UMaine didn’t have a history of consistent research into songbird migration in the gulf until the start of the Network, which originated through an event that occurred about five years ago. At the root of the network was a 50-year-old seabird restoration project being done by the Holberton’s lab in collaboration with the U.S. Fish and Wildlife Service. It took a specific incident for things to turn. Holberton says she was on Petit Manan Island one early May day about four years ago with a graduate student studying the Arctic tern when the pair realized they were surrounded by songbirds.

They set up a mist net — a fine mesh netting used to catch birds — and within five minutes, they had captured a number of songbirds.

“U.S. Fish and Wildlife colleagues were there,” Holberton says, “and they could see that songbirds use these islands. They began to write their long-term, comprehensive management plan trying to understand how the islands they manage for seabirds during the breeding season are important for songbirds during other times of the year. They started to put songbirds on their radar screen.”

Working with USF&W and National Audubon, the network selected islands for research and banding based on the amount of involvement already present there in bird research, and also the level of logistical support the islands were receiving. The area of Metinic Island where Leppold’s banding station is located, for example, is owned by the Maine Coastal Islands National Wildlife Refuge, which services the banders with bi-weekly grocery deliveries and shuttling researchers on and off the island.

One of the key undertakings for the Network is bird banding, an effort in which Leppold plays an important role. This spring, Leppold will head back to Metinic Island for the beginning of her fourth overall migration season there. She will spend hundreds of hours banding birds, taking measurements, counting birds by hand, and performing the release tests.

Leppold’s job is to gain an understanding of the types of birds landing on Metinic, why they’re there and the condition they’re in when they arrive. Other network banding stations have been set up at Petit Manan and Seal islands and Petit Manan Point. UMaine biologist Brian Olsen has three banding stations in Acadia National Park under his purview, including two operated by UMaine graduate students.

During the fall 2009 season, more than 3,000 birds were captured at Metinic, Seal, and Petit Manan islands. Holberton says, taking into consideration statistics such as the number of nets and people available to monitor the nets and handle birds, the amount of migrants captured per net hour were almost double at Metinic compared to the other two islands. Metinic was equally as busy during the fall 2010 season and the intensity of birds captured there far exceeds that of other stations, including Manomet Bird Observatory, a long-term and much more expansive operation in Massachusetts.

In order to band birds, workers set up mist nets between two poles several dozen feet across. Birds fly into the nets and are collected by banders, who process each bird by taking measurements and affixing a specially sized and individually numbered U.S. Geological Survey aluminum band to one of the bird’s legs. The bird is released into the wild ideally no more than 30 minutes after it’s been caught. If workers are overrun with birds, as happened occasionally on Metinic, they will close the nets so no more birds are caught.

After a bird has been banded, the bander determines the sex and attempts to age the bird, and measures the wing and tarsus on the bird’s foot in order to get an idea of its body size. An important step for Holberton’s research is approximating the amount of subcutaneous fat on the bird. The researchers can use the fat amounts, as seen through the skin in the bird’s neck region, and body weight to get an idea of the bird’s energetic condition.

If a bird has more fat on its body than normal, taking into account its mass, researchers can extrapolate that the bird is in good energetic condition and is piling on weight to prepare for long migration flights. If a bird is lacking in fat, it may be at the end of a migration or has been unable to put on enough weight for a long trip. The better energetic condition, the longer a bird can go in the air, which means taking shorter routes by cutting across bodies of water where there are few opportunities to land. The reverse is also true: Birds in poor condition will tend to move inland, where there may be more opportunities to stop, but there may also be a greater danger posed by predators and longer distances to cover.

To describe three different types of stops migrating birds tend to make, Holberton uses terminology known in bird biology circles. Some landing spots are known as fire escapes — places where birds stop for a few hours to get a quick rest or reorient themselves after having been blown off course, but aren’t suitable for long stays because of lack of food or shelter from predators. Then there are the so-called convenience stores, which have easily accessible resources for birds. Here they can rest briefly for a day or two before moving on to better sites, maintaining or improving their condition and increasing the odds of reaching their destinations. The third type of spot is the five-star hotel, a place where birds can stop for a week at a time to rest, feed and fatten in order to make long pushes on their migratory travels.

So far, Holberton and her researchers have determined that Petit Manan and Seal islands are more in the life preserver category, offering critical places to rest, while Metinic falls into the convenience store analogy, where a bird can improve its condition and therefore increase its chances of reaching its destination. Both of these are vital links along migratory flyways. Fortunately, there are also five-star hotels in the Gulf of Maine, too, and all of these areas are regarded as critical habitats for migratory birds.

Where in the gulf those places are located is one of the big pieces of Network researchers’ work. When hot spots such as Metinic have been plotted, scientists will know which areas and the flyways connecting them should be protected from development or coastal wind turbines.

“That’s really what drove the formation of the network,” Holberton says. “Energetic condition is really important to know. There are a lot of birds in these areas but we don’t really know who they are, how many there are, where they’re coming from, where they’re going, and why. We need to figure out the location of the important stopover areas.”

When banding, Leppold sometimes takes a tail feather or small amount of blood from the birds. From those biological materials, the UMaine researchers have been able to determine where birds were born or bred by looking at the stable isotope signatures of those samples.

An isotope is a form of a chemical element that contains a different number of neutrons than its normally occurring form. A stable isotope is one that doesn’t give off radiation over time. Scientists can track the presence of a stable isotope, known as a signature, in a bird that has over time been a part of the food chain. Take, for example, a hydrogen stable isotope known as deuterium that naturally occurs in the environment. Its levels rise in the environment where there is a lot of water, including geographic areas that have received a lot of rain.

Plants take in the deuterium, which is incorporated into their tissues through photosynthesis. Plants are eaten by insects, which incorporate the deuterium into their bodies. Birds eat the insects and therefore the stable isotope is transferred through the food chain and gets incorporated into the growing tissues in the bird.

Stable isotopes can be measured in something like a feather, which incorporates the proteins with the stable isotope signature. Even if the bird moves to a different habitat and the feather grows out, the stable isotope signature of the original habitat will be found at the end of the feather, giving an indication of the kind of environmental conditions into which the bird was born. The carbon signatures in the feather closer to the bird’s body can give researchers an idea of what kind of environmental conditions a bird has been more recently for breeding purposes.

If the range of stable isotopes is available for a large region, such as the Americas, researchers can then map the geographic areas that have specific levels of those stable isotopes.

If Holberton finds the deuterium signature in the feather or a bird, she can therefore assume the bird has at some point been in an area that has had a lot of water. That might seem too broad a geographic area to be of help to researchers, since there are rainy seasons all over the world, but scientists can look deeper to gain specifics. If Holberton has a feather from a bird known to be in Alaska and Newfoundland, for example, she might check the stable isotope signatures against those commonly noted in those areas to determine where a bird has been.

“You can find different habitats anywhere in the globe, but the rain patterns vary north and south,” Holberton says. “By also measuring stable carbon isotopes, which can vary with habitat type, in the same tissues, you can start putting another coordinate on where that bird was. So we’re taking these different tissues that give us a different time stamp, and we’re putting together a composite of stable isotope signatures that help give us some information.”

The information again informs the Network’s research by revealing more about birds’ travels.

Blood samples are tested for indications of the birds’ immune health. Holberton checks for ratios of hetereophils, which are ever-present immune cells that fight bacterial infections, and lymphocytes, which are cells that provide a longer-term line of defense yet have a high cost to a bird in terms of the energy it takes to produce them. If researchers find elevated levels of heterophils and normal levels of lymphocytes, the assumption is that the bird is fighting an infection but hasn’t yet suffered any long-term consequences. However, if lymphocyte levels are low, the testing may indicate the bird is having trouble maintaining its immune response critical to survival.

“A lot of times we see a situation where birds are not fighting an infection yet, but they’re under some kind of stress, whether the stress is from bad weather or crowded conditions, or they can’t find enough food,” Holberton says. “The immune system is a luxury that’s only going to be good if the animal stays alive, so what animals do is redirect energy away from the production of lymphocytes in order to deal with the currently stressful situation. They can become immunosuppressed and more susceptible to infection and disease. Things that you might normally have thrown off, like a cold, can kill you.”

Energy metabolite levels also can indicate changes in the behavior and physiology of a bird. If those levels are elevated, combined with indications of changes in the immune system, it could indicate that the birds isn’t doing well. That means it’s more likely to make a lot of stops during migration, which means taking a longer journey around the gulf. Birds in good shape will cut across large bodies of water, because they don’t need to stop as often.

Another important element of research for the Northeast Regional Migration Monitoring Network is data picked up by both radar and passive acoustic surveys. The acoustic data, gained through recorder arrays throughout the Gulf of Maine coastline and inland, give researchers an idea of which species of birds are flying overhead, especially at night.

As birds move through the sky, they call to each other via a series of short, usually high frequency noises, many lasting a mere hundreds of a second, which sound to us like clicks or chirps. An interactive sound analysis software system called Raven, which was developed at Cornell University, translates each call into a spectrogram or visual picture of the sound.

A group of UMaine undergraduates working in Holberton’s lab compare each bird’s song picture to standard, confirmed images of a species’ spectrogram to determine which species of bird has made the call.

“It puts a face to the radar profile, and allows us to identify different species flying overhead,” Holberton says. “Some species may not call, so this technique doesn’t tell you what’s not flying overhead. But this does help give us an idea of what is overhead in a certain time period and the corridor of the birds’ movements.”

Acadia University biologist Phil Taylor’s work also adds to the network’s diverse research techniques, especially related to individual songbirds. In addition to operating the Network radar sites, a graduate student in Taylor’s lab is deploying tiny transmitters on small songbirds as they are captured at banding stations in southwestern Nova Scotia. As the birds move through the Gulf of Maine, automated receivers set up along the coast from Nova Scotia to Scarborough Marsh can detect the flight and stopover movements of the individual bird.

Citizen research is also expected to be part of the project, with bird-watching fans in the populace recruited to help identify bird species and enter their observations into a database.

“No one research method by itself will tell you what you want to know,” Holberton says. “The value of the Network really is the integration of the different methods and the extensive expertise of the collective group of participants. That’s the beauty of it.”

The amalgamation of the Network’s research is expected to offer a clear picture of how migratory songbirds and other migratory species such as waterfowl, seabirds and shorebirds, are using the Gulf of Maine. Evolutionary changes in birds likely won’t keep up with human alterations to landscape, but at least scientists will know what species are flying through the area, how the birds are using different areas of the gulf, and how their numbers may be changing in the face of environmental challenges. Holberton’s own research over the years has focused on the Blackpoll warbler, a boreal forest breeding bird that undertakes one of the longest non-stop migrations in North America. But in 2005, a report by the Alaska Department of Fish and Game claimed Blackpoll warbler populations have declined as much as 90 percent in Alaska and western Canada.

How does the changing climate have the potential to affect the Blackpoll warbler populations – and provide an example of why the Network’s research is so critical? In years when there are a lot of hurricanes along the eastern North Atlantic where these warblers fly non-stop from the eastern U.S. to winter throughout the Amazon River basin, the warblers suffer devastating losses as they migrate during hurricane season.

“In a 40-year period, say, you run those chances,” Holberton says. “But what do we heard every year? Hurricane frequency and intensity have increased over the few decades and they’re going to increase more. Studies by Manomet Bird Observatory researchers have show a strong correlation between storm frequency and decline in Blackpoll numbers over the last three or four decades. The Blackpolls can’t evolve fast enough to adjust their migratory behavior to avoid that. It’s easy to get complacent with a species that’s always been considered so common and overlooked. The population loss hasn’t even made the headlines but it’s one that could slip very quickly.”

Climate change isn’t the only potential threat to birds migrating in the Gulf of Maine, although it’s one of the biggest. Land development along the coastline could change how birds use their stopover sites; the gulf could see more areas with fire escape capabilities, for example, while there are fewer five-star hotel zones, a situation that could not sustain successful migrations of millions of birds annually.

More and more commercial developers and communities are looking to coastal or near-shore areas for sources of wind energy. Deep-water wind platforms are in the experimental stages, but may pose the least risk to birds and also bats. Holberton, her team at UMaine, and the rest of the Network researchers hope their findings will be used to support responsible development in and around the Gulf of Maine, especially now that researchers such as Leppold have shown the region is a superhighway for songbirds and other species.

“Maine desperately needs a comprehensive, long-term plan for coastal and offshore development that takes into account not only our region but those north and south of it,” Holberton says. “These birds that travel well beyond the Gulf of Maine are very good at what they do, but it might not take much more than one thing, such as loss of critical migratory habitat in addition to loss of wintering and breeding areas, to push them over a threshold at which they can no longer sustain their populations. That’s the issue.”


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