Year of the Bird Series: April – Tree Swallow

Editor’s Note: 100+ bird organizations declared 2018 the “Year of the Bird” as it is the centennial of the Migratory Bird Treaty Act’s ratification. Many are pledging to do 1 thing per month to help birds. As Ruthven Park National Historic Site has a bird banding station in collaboration with the Haldimand Bird Observatory, we are featuring one blog post per month on different birds! Below, you will find the fourth installment in this 12-part series.

Article by Christine Madliger, Post-Doctoral Researcher (University of Windsor and Carleton University)

Wetlands, riversides, and meadows have just recently seen the return of this month’s “Year of the Bird” entry – the Tree Swallow (Tachycineta bicolor). This feisty, beautifully-plumaged songbird will always be high up on my list of most favourite birds. For six years, my husband (Chris Harris) and I studied the tree swallows nesting at Ruthven Park, focusing on how habitat quality affects their stress hormone levels. As you drive up to the main expanse of the park or explore the surrounding areas, you can see a whole collection of wooden bird boxes (see photos below) where this species builds its nest and raises one set of 5-6 young each spring/summer. Tree swallows can also be found nesting in natural cavities in trees, but they do not have the strong beak required to excavate these cavities themselves. Instead, they rely on woodpeckers to do the work for them! Right now, females are busy choosing their mates for this season, assessing potential suitors by the blueness and shininess of their feathers.

To many birdwatchers and ornithologists, tree swallows are considered a common bird. Some have even gone so far as to call tree swallows the “white rat” of the bird world because they have been studied in such great detail. Part of the reason for their popularity as a study species stems from how accessible they are while nesting. Colonies of nest boxes allow researchers to easily monitor the birds and learn more about their reproduction, plumage colour, behaviour, physiology, and how they respond to climate change. Despite being small birds that only weigh around 20 grams, they are also very hardy. This means that researchers and bird banders who monitor colonies of nest boxes can capture the birds to band them, take measurements and weights, and even acquire small blood samples, without interfering with the bird’s ability to successfully breed.

Despite being so highly studied, scientists still have a lot more to learn about this species, especially regarding their migration and over-wintering ecology in places like Mexico and Cuba. Tree swallows are part of an interesting group of birds known as aerial insectivores, which also includes the martins, swifts, flycatchers, and nightjars. This diverse group all shares one thing in common: a reliance on flying insects as their primary food source. Compared to all other groups of birds in North America, aerial insectivores are in the sharpest decline and scientists are still trying to determine why this is so. Even tree swallows, which are quite abundant and widespread, have been showing population declines since the 1970s. Most likely, there is an assortment of factors driving this decline, including habitat loss and decreased availability of food sources.

One method that scientists are using to learn more about what might be contributing to tree swallow declines is an exciting type of tracking technology. Geolocators are comprised of a light sensor and a computer chip and are fitted to a bird’s rump with a special harness. They are light-weight enough that the birds can carry them year-round. By recording the timing of sunrise and sunset, geolocators allow researchers to determine the approximate location of a bird on any given day. Recently, scientists at the University of Guelph led a study that put geolocators on tree swallows at breeding sites across North America. The birds traveled to their over-wintering locations and then researchers retrieved the geolocators and data the following year when they came back to their breeding sites. This work has located crucial stopover sites along tree swallow migratory routes and is helping to pin-point the most important locations for conservation work.

If you have the opportunity to visit Ruthven Park this spring, stop at a distance for a few moments and observe the tree swallows using the nest boxes around the mansion and banding lab. You may see males vying in the air to claim possession of a highly-coveted waterfowl feather, which they use to beautifully line their nest (see photo below). Or you may hear a male and female chatting away at one another, their song a pleasant assortment of bubbly gurgles and chirps. Visit a little later into the spring or in the early summer and you will see both parents flying out over open water and fields, collecting mouthfuls of squirming insects to feed their hungry young. Regardless of when you happen upon them, these common but beautiful birds are certainly worth a closer look.