Aerial acrobats of the biosphere: Swallows

A young Tree Swallow and its parent are pictured in a nesting box.

During this year’s Bras d’Or Watch field day on July 14, participants noted flocks of swallows (Mi’kmaq: pukwales) at all five sites. These charismatic acrobats were quite numerous and entertaining.

Their apparent abundance is of interest because swallow populations worldwide are facing significant population declines. In 2014, the alarm bells went off among North American bird watchers. Several swallow species had experienced greater declines than any other group of birds in North America, with the most severe downward trend in the Maritimes. The most likely reason for this dramatic decline has been the significant decrease in the biomass of flying insects due to agricultural insecticide use.

In the Bras d’Or Lake Biosphere, we have four species of swallows that breed before their annual fall journey to more southerly climates. Their common names are derived from their preferred nesting habitat; Tree, Barn, Cliff and Bank Swallows. All four species are aerial insectivores, catching mosquitoes, bees, horse flies and other flying insects in mid-flight.

The species that is most common in the Biosphere is the Tree Swallow, and that species is most likely the one that entertained Bras d’Or watchers on field day. Tree Swallows are beautifully streamlined little songbirds with long, pointed wings, a short, square or slightly notched tail and short, flat bills. As is the case with most birds, the males are the showy sex with blue-green above, white below with black flight feathers and a thin, black eye mask. Females are less showy, with more brown on their upper body.

Contributed photos — Pictured is a Tree Swallow.

Globally, the International Union for the Conservation of Nature lists the Tree Swallow’s status as “least concern” but the situation in eastern Canada was dire between 1966 and 2014 with a significant population decline. This decline could be a function of the sparse food but it could also have been a result of a decline in nesting habitat. Biosphere Tree Swallows nest in tree cavities in open habitats such as fields and marshes close to the Bras d’Or estuary. If old trees with cavities are in short supply, Tree Swallows are happy to take advantage of provided nest boxes. If you are handy and would like to build a nest box, see the instructions at: If you need encouragement to undertake this project, remember that they eat blackflies, mosquitoes, wasps and horseflies.

Although Tree Swallows are the most common, you may observe one of the other species that call our Biosphere home. The smaller Bank Swallow has a slightly forked tail, short pointed wings, a chunky body and large head. They nest in large colonies by excavating their own tunnels in steep sandbanks. Sometimes they share the nesting habitat with Belted Kingfishers. If you see one flying you will notice a thick brown band across its white chest, unlike the pure white chest of the Tree Swallow. As their name suggests, Bank Swallows breed in open lowland areas near bodies of water, excavating nest hollows in the sides of banks.

The Committee on the Status of Endangered Wildlife in Canada has assessed the Bank Swallow as “threatened” because the Canadian population has declined 98 per cent over the last 40 years. As is the case with the Tree Swallow, the decline is probably a result of loss of breeding habitat and decline in prey abundance.

Another resident, the Cliff Swallow, has rounded wings, a small head, and a square tail. This species is slightly larger than a Bank Swallow and much more brightly coloured. If the light is good, their backs will appear dark blue metallic and their rumps pale orange. Their little faces are red with a white forehead patch. When feeding in flocks with other species of swallows, they often fly higher. They build mud nests in colonies on cliff ledges or under bridges. The population of Cliff Swallows is not declining as precipitously as other species and is not currently of concern.

The species that is of most concern currently is the Barn Swallow. This species is cobalt blue above and tawny below with a very long, deeply forked tail. As their name suggests, they build their cup-shaped mud nests almost exclusively on human-made structures such as barns. Before barns were abundant, this species largely nested in caves. The Committee on the Status of Endangered Wildlife in Canada lists this species as “threatened.”

Have you noticed flocks of acrobatic swallows in our Biosphere? We would really like to have a better idea of how our four species are faring. If you see swallows, take a photograph and lodge your information on I-Naturalist at:, a Web-based platform which is very easy to use.

So, when you go on a drive or hike in the Biosphere, remember your cell phone and watch for our aerial acrobats!

Dr. Annamarie Hatcher is a consulting ecologist and a board member of the Bras d’Or Lake Biosphere Reserve Association. Information about swallows was obtained from the Nature Conservancy of Canada at: For more information about the Bras d’Or Lake Biosphere Reserve Association, please visit: their Facebook page: