Dusk for the Kent Island Tree Swallows

On Kent Island, everyone dabbles in each other’s projects, and the lines between artist and scientist are often blurred. When Nathanial Wheelwright, a former director of the BSS and chair of the biology department at Bowdoin, asked Hannah, Tracey and I, the non-bio majors, if we wanted to take up a side-project on tree swallows, we jumped at the learning opportunity. Tree swallows are small, insect-eating birds with a distinctive long wings and dark feathers with an iridescent sheen.

Tree Swallows have large wings with tapered feathers, allowing them to perform the aerial acrobatics necessary to catch insects (image:http://en.wikipedia.org/wiki/Tree_swallow)

Tree Swallows have large wings with tapered feathers, allowing them to perform the aerial acrobatics necessary to catch insects
(image:http://en.wikipedia.org/wiki/Tree_swallow

They have a long history of nesting on Kent Island, but sadly that era has passed its twilight and is falling swiftly into darkness. In first annual Kent Island scientific station report  Bill Gross, one of the “Bowdoin Pioneers” who began science research on the Island in 1934, describes tree swallows as “our greatest friends,” possibly referring to their services as mosquito predators. The report also reveals that the Pioneers built bird boxes for the swallows. Many of the boxes that still dot the Island today are remnants from studies of tree swallows conducted in the 1970s. Professor Wheelwright continued this research on tree swallows when he arrived on the Island in 1987, and has seen a dramatic decline in the population in the quarter century that he has kept tabs on the birds. “In the 80’s there would be 100 males sitting in that single tree,” he told me, pointing to a now-barren spruce in front of the dorm. By 1994, the population was down from 100 pairs of tree swallows to 60 pairs, and that summer the constant rain and fog killed all of the chicks, making matters much worse.

It was after four or five years of low tree swallow numbers that Professor Wheelwright realized the decrease was a trend and not just annual variation. “The habitat on Kent Island hasn’t changed, so it has to be something affecting their migratory route or wintering grounds,” he explained. Habitat loss and insecticides, which poison swallows’ food source, are the most likely culprits. While Tree Swallows do not have threatened species status under the IUCN, global populations declined 36%  between 1966 and 2010. Tree swallows aren’t the only bird species that has seen major population decreases in recent years. Scientists on Kent Island have observed far lower densities of herring gulls, chickadees, and many other species that once crowded the Island. Researchers discontinued upkeep of the tree swallow bird boxes because there simply weren’t enough birds to make the effort worth it.

Our project is to resurrect the tree-swallow study to take stock of what remains of the population on the Island after years of neglect. Wheelwright armed us with a map of the Island, a bucket of nails, a notebook, and a hammer, and set us loose into the field. Our task was to check each bird box that dots the grid of quadrants that overlays the South and North Fields. We noted which houses were rotting or missing a door, which contained old nests, and which, if any, had active nests. After finding many empty houses and several lying on the ground, slowly decomposing, we found a nest that contained five chicks, one unhatched egg, and one remarkably calm female tree swallow. The chicks had probably hatched that morning, and were naked pink blobs that were so entangled that it was difficult to count them. Professor Wheelwright assured us that the common wisdom that touching baby birds will make mothers reject their chicks is a myth, and after we closed the box door and backed away from the nest, the female swallow swooped down and returned to her brood. We only found one other nest containing five unhatched eggs, though there is a possibility that other tree swallows might build nests in the coming weeks. The eggs take fifteen days to incubate, so we will have to carefully time our visits to keep track of the hatch date. Later in the summer, the team that studies Savannah Sparrows will help us to band the birds, which hopefully will return to the Island next year. I’m excited to have my own field project, not only because I will get to work with baby birds but also because it will require me to sharpen my vision. Observation of the natural world is a skill that many people have forgotten because they no longer have to do to it to survive. Professor Wheelwright has reminded me to keep looking, because it’s amazing how much you can learn about life from keeping track of what you see.

Tree swallow nest, lined with gull feathers (image:http://www.sialis.org/neststres.htm)

Tree swallow nest, lined with gull feathers
(image:http://www.sialis.org/neststres.htm)

Sources:

Gross, W.A.O. 1936. Kent’s Island — Outpost of Science. Natural History 37: 195-210.

Hébert, P.N. 1989. Decline of the Kent Island, New Brunswick, herring Gull, Larus argentatus, colony. Canadian Field-Naturalist 103(3): 394-396.

The Cornell Lab of Ornithology, “Tree Swallow.” All About Birds: 2014. http://www.allaboutbirds.org/guide/tree_swallow/lifehistory

 

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