Today Tracey, Hannah and I continued our project to monitor and band the two Tree Swallow families on Kent Island this summer, the last of what used to be a large population. We had to time our expedition carefully, to catch the hatchlings when they were big enough to band, but before they fledged and no longer returned to the nest. We checked the nests every other day to see if the eggs had hatched, because checking daily might put too much stress on the parents and cause them to abandon the nest. Nat told us to band the chicks thirteen days after our estimated hatch date, because the nestlings fledge twenty or so days after they hatch. While Nat had helped us to band the females earlier in the summer, he departed for Brunswick, leaving us with what he had taught us of bird fieldwork. We also had the help of Jackson, who studies Yellow Warblers, and Raquel, from the University of Guelph in Ontario, who is working with Savannah Sparrows. We approached the first box and were immediately warned off by a Herring Gull, who swooped threateningly and landed directly on top of the tree-swallow box. We soon realized the reason for its aggression when two Herring Gull chicks emerged from the high grass onto the path, squawking and scurrying on their awkward legs. After shooing the chicks away from our makeshift banding station of an overturned crate and warding off the parent gull with a stick, we approached the tree swallow box for a second time.
The first thing Raquel said when she opened the box and removed the female from the nest was, “Are you sure these aren’t adults?” A huge transformation had occurred in the two weeks since we had last checked the chicks. What had been five flesh-colored blobs that Nat described as “tangled spaghetti” was now a mass of grey and white feathers and wide, yellow mouths. These nestlings were much larger than the Yellow Warbler and Savannah Sparrow nestlings that Jackson and Raquel had banded before. It was hard to tell which appendage belonged to which nestling, but we eventually figured out that there were five, as well as an egg that is unlikely to hatch at this point. Extracting the nestlings was difficult because their tiny hooked claws gripped the nest with surprising strength, but Raquel gently removed two and put them in a bird bag. We went through a similar process of banding, measuring, and weighing the birds as we had done before to the female swallows, except that the nestlings were much more difficult to hold. The “photographer’s grip” of necks between peace-fingers was less possible because the nestlings tucked their heads in and barely had necks to begin with, so we ended up cupping them in our hands. Jackson showed me how to hold a tree swallow with one hand while stretching out its leg between two fingers and using my other hand to close the metal band around its tarsus, the area between the bend in its leg and its foot. Banding is an extremely delicate process, because a band that is too tight can damage the leg and cause infections, severely reducing the bird’s chances of survival. The birds wiggled when we held them and even managed once to escape, but did not make it very far without the ability to fly. After processing the birds as quickly as possible, we returned the birds to their nests as quickly to placate their anxious parents, who swooped near the box helpless to prevent us from taking their babies.
The nestlings in the second nest were about a week younger than those in the first, and the difference in their appearance made the rapid growth that tree swallows undergo in their first few weeks very visible. They only had the beginnings of feathers, and Jackson pointed out the yellow fat deposits on their bellies and tarsus that were visible beneath their thin skin. When I held a nestling, it lay in my palm and wiggled its miniature wings helplessly.We banded two before deciding to wait another few days to band the remaining three, because the fat on their tarsi made it difficult.
It was incredible to not only see all of the stages of the tree swallow’s growth, but also to be able hold the bird and feel its life in my fingers. While I was glad to have that experience, I also felt guilty for disturbing the tree swallows during a delicate developmental period, and for causing them stress that might damage their chances of success. Many scientific experiments, even if they mainly involve observation like our project, involve disturbing the study subject. Scientists take measures to minimize interference, but some damage is often inevitable. I was comforted by the thought that our project is for the larger purpose of conservation, and that our future efforts to fix tree swallow boxes will provide habitat for next year’s birds. I am hopeful that some of the nestlings that we banded will return to their birthplace, though only 20% of tree swallows survive their first year. Despite these odds, all but one egg hatched, and the birds survived what can be fatal stormy weather. I was heartened by their fierce will to survive that I sensed even as they lay prone in our hands.