Thursday, August 20, 2009
The Search for A Patch of Green: Appledore Island and Bird Migration
by Andrew Powers, Dalhousie University
It is 7:00 AM and it is time to "walk the line" for netted birds. Stella Walsh walks ahead and a certain amount of excitement starts to build up in the visitors. The nets wind through the forest, ending just out of view. A person’s heart could almost stop at the electrifying moment when a fluttering bird is in the net. This causes the net, which formerly ebbed and flowed like the sea, to jump and quiver instead. Walsh carefully extracts the bird feet first, then the wings, and finally the head. She explains that in removing the bird there is no strict set of rules. The bander will often also softly speak to the bird to try and calm the squawking beast, while expert fingers work to release it from the net. However, these birds are not being caught just for fun. They are often passing though on their way to tropical climates and back again. It is hard to imagine an animal that weighs a couple of ounces traveling for thousands of miles on delicate wings every year. The migration patterns of these birds force the banders to have some of the longest working days, often from sunrise to well past sunset.
The banders are working hard here because it’s an island six miles off the coast of Maine, which is very different than most other banding stations. Although Appledore Island is far away from the mainland, birds are still plentiful here. This fact goes against what popular opinion might believe about animal populations in a small area, that they are small in number. This fact begs the question, why are so many birds stopping here?
Three banders are working this August to further explore this mystery. During the two major migrations, to and from the tropics, birds use Appledore Island as a stopover spot in the Gulf of Maine. They follow a specific path using a magnetic bearing, much like a compass that takes them on the same route every year.
These birds are not only here for a quick stopover though. The island is also home to several species of nesting birds, some of which do not migrate at all. The non-migratory birds need to be tough enough to survive the harsh winters, which is a different strategy of survival than that of the birds which are able to migrate, which need to be able to store enough energy for the long flight. Of the nesting birds, both the migratory and non-migratory birds lay eggs on the island in the spring. The younger birds that hatch stumble into the nets more often than the adults, and can be more easily banded.
Banding is not a perfect science, but it is cheaper than satellite tracking. Bands cannot always be recovered, as compared to more expensive means. However many bands can be added to many birds so that there is a greater chance of viewing a trend in the information, such as life span. Through this banding, researchers on Appledore have discovered that birds use the island as a stopover on migration. Every year some of the same birds have been found in the nets, showing that the animals are using the island as a rest stop while traveling the highway of the sky.
David Holmes, a master bander on Appledore, states that in the springtime, it is common to "see birds fall out of the sky, at least in the old days, until 10 in the morning." The vast number of these migrating birds stopping on Appledore can be visually seen by scanning the skies for birds quickly dropping down from high in the air. Holmes knows this fact from experience as he has been on the banding staff for thirty-three out of the thirty-five years that the Shoals Marine Lab’s banding station has existed.
Holmes, when off-season, spends the year as a piano and flute instructor. Another bander, Stella Walsh spends the off-season as a healthcare worker, filling out paperwork. Holmes describes bird banding as one of the few fields that "citizen science" can make a real difference. Even though the banders do not pursue their summer passion at home, they are still have to be well trained to be able to band correctly. It is rare for a citizen to pursue such a difficult science that can take five to ten years to master. These citizen scientists must also have more drive than their university scientist counterparts as they are paid little or no money for their skills
The banding and measuring process is both challenging and extensive. After the bird is netted, the magic begins. It is then brought back to the lab to take measurements. These include leg length, stored fat, feather patterns, and the weight of bird. An unbanded bird will also have a band added to the leg. The band assigns a "serial number" to identify each bird for its whole life. Individual banders carefully work to reveal these facts and are luckily at the Shoals Marine Lab station, working hard on the opening morning of the season.
The small reddish-brown bird that has been captured is slowly being removed from the net, while fluttering its wings and chirping.
It is important to keep the birds calm during this procedure so that no injury will occur. "The first concern is the welfare of the bird," Walsh instructs. The smallest injury, such as a broken leg or damaged wings, could eventually cause death.
Walsh places the bird in a bag and carries it back to the station, where the other banders are patiently waiting after their data work. Holmes then steps forward to meet the bag. Walsh removes the bird from the bag, to have Holmes point to the bird and ask the visitors, what they might guess as the species of bird. He draws attention to some certain details of the body such as the slightly curved bill and the held up tail. Holmes identifies it as a young Carolina Wren, which has an unusual life on the island.
Maine is at the northern end of the Carolina Wren’s breeding range. These birds have traveled to Appledore and are non-migratory. In the mid-1990’s the population was literally wiped off of the island due to an extraordinarily harsh winter and the bird’s sensitivity to cold. It then took five years for the wrens to return and breed again. This is a prime example of the dangers a non-migratory bird will face on Appledore island or even elsewhere.
An island’s climate is unique compared to the mainland because it has less snow, due to the warmth of the ocean. However in addition to this, it often has more wind, which cannot be blocked by large trees. There are no tall trees on Appledore Island because the soil is not deep enough for them to take root because after a relatively thin layer of soil, the roots hit thick bedrock.
Despite the lack of these trees the island can still provide a refuge to the migrating birds through the smaller shrubbery. Fruit-eaters, such as Cedar Waxwings arrive here to take advantage of the fruiting plants such as cherries. However, cherries are not always as abundant as the birds might hope. During the summer an insect called a webworm, will cover cherry trees in thick webs and feed on the tree. These trees then produce less food for these birds that then cannot get the energy they need. "Birds have flown over all this water to a patch that’s supposed to be green" Holmes sadly states. This change can reduce the chance of the birds surviving to the next stopover and can be tough on a population.
Appledore migrating birds have been recorded as far North as Newfoundland and as far south as Venezuela, but this journey can only be possible by the maintenance of these stopover sites. If the food and shelter are good enough there, then a bird can make it from stop to stop, all the way to its best breeding and feeding grounds. Banding has shown that in addition to the migration stopover, some birds also find it to be more successful to use the island as a breeding spot or even to spend their whole lives on. However, no matter the reasons for birds to be on Appledore, it is vital that this unique area be preserved so that we may still have as many feathered wonders as we do today. This island is not the only place in the world that birds migrate through. There are many other stopover spots in the world, each for an individual type of bird, such as large bodies of water with lots of plants for ducks, and dense woodland filled with insects for warblers. These areas need protection to save birds and ensure avian survival into the future.
[Photo by Colleen Cassidy]