Home - Songbird Superhighway – Spring 2011
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.”