Swooping, soaring and flying in beautiful patterns in the sky. These social birds capture the attention and interest of many by swarming around bridges, overpasses and fields in the summer. Yet, rarely are Cliff Swallows seen without the company of another. Feeding off of each others’ energy, I don’t think this bird quite knows the definition of “alone time”.

Description + Identification

Weighing in at 19-34 grams, the Cliff Swallow is a small bird with both adult females and males measuring 13 cm in length and flying through the sky with a wingspan of 28-30 centimeters – comparable to the size of a sparrow (All About Birds). As with most birds, the light conditions in which you see it will affect the colours and patterns the human eye can identify. Under poor light, Cliff Swallows appear brown with dark-coloured throats and a white underbelly. When in good light, the observer can see that their backs are metallic, dark-blue with pale brown-orange rumps. Their faces are a rusty red with a bright white patch above their bill. There are no distinctively different identifying features between the female and male Cliff Swallow. However, the juveniles appear as messy adults with pale, rusty red faces and a dingy-looking breast.

The best time to find this bird is in the summer when they are swarming to hunt insects. They will likely be foraging in flocks close to fresh water, such as lakes, rivers, or wetlands. Key features which differentiate the Cliff Swallow from other common swallows in North America are their square tail and the pale brown-orange rump on their dark upper body (Sibley, 2016). They also tend to forage higher than other species, so turn your gaze high to the sky.

Vocalizations

Cliff Swallows have a limited vocal repertoire with five distinctive vocalizations for signalling actions such as feeding, raising the alarm and mating (Loesche, Beecher & Stoddard, 1992). Songs are reserved for activities related to breeding like courting and nesting. The Cliff Swallow sings a combination of squeaks and gutteral grating sounds in six second intervals. The most common Cliff Swallow call sounds like a soft chur. Calls during foraging sound like a squeak, while calls alarming the rest colony about danger sound like a purr.

Habitat + Distribution

Like its namesake, the Cliff Swallow habitat orginates in the western mountains nesting on cliff sides and rock ledges in large colonies. Presently, however, their nests are more likely to be found on human-made structures such as bridges and house eaves (Blair, 1996). Cliff Swallows live in grasslands, towns, and river edges while avoiding areas of heavy forest and deserts (All About Birds). It’s likely to find most nesting colonies close to a water source and open fields which are optimal for foraging (All About Birds).

Nesting

Although Cliff Swallows can nest in solitary, they are far more inclined to nest in colonies. The farther west in the Cliff Swallows’ breeding distribution, the larger the colony can be. Colonies can reach up to 3,700 nests in one distinctive habitat (All About Birds)! You can spot nests on a variety of structures such as cliffsides, building eaves, bridges, and large trees. Each nest is built between a vertical wall and a horizontal overhang. Cliff Swallows gather mud in their bills and bring these mud pellets back to mold them in place. Each gourd-shaped nest contains upwards of 9,000-12,000 mud pellets costing an abundance of energy and time to build this nest (Gauthier & Thomas, 1993)! Even though both the female and male nesting pair contribute to making the nest, that is still 4,500-6,000 trips back to the mud source.

Behaviour

As aforementioned, the Cliff Swallows are an extremely social bird. They feed, bathe, preen, nest, and migrate in groups – talk about a commune! Sightings of Cliff Swallows are common as they forage for a variety of swarming insects during the day. On a clear, warm spring or summer day, they can be found over grassy meadows and other open areas feeding in groups from 2 to over 1,000 birds. Cliff Swallows take advantage of thermal air currents which bring together the swarmming insects causing less energy expenditures during foraging. If out birding on a rainy or cool day, it is more likely to find the Cliff Swallows foraging over fresh water (All About Birds).

These social birds turn to their neighbours in the colony if they find themselves unsuccessful during a hunting trip. Individuals who have returned to the colony unable to provide for their family, or hungry themselves wait in their nests until they notice another come back with food. Often, the successful individual will alert the rest of the colony by giving a specific call. The unsuccessful individuals can then follow the successful neighbour ensuring they are all well fed (Brown & Brown, 1997). It is truly a community effort to ensure the benefit of all.

Conservation Status

The Cliff Swallow is showing widespread decline of population in Canada (Migratory birds, Government of Canada). During the 1980s, there has been an overall decrease in species known as avian aerial insectivores (i.e. swallows, swifts, nightjars, and flycatchers) across North America (Smith et al., 2015). While the causes of the decline in these species remains uncertain there have been changes in swarming insect populations resulting from the use of insecticides (Hallmann et al., 2014). Another factor which contributes to the population decline is the invasive species of House Sparrow which steal Cliff Sparrow nests, contributing to their overall breeding success (Leasure, Kannan & James, 2010). Even though the Cliff Swallow population is declining in Canada, the conservation concern remains low as their abundance in other parts of the continent balance out these numbers (All About Birds).

Human Impact on Cliff Swallows

As previously discussed, the urbanization of once natural landscapes have altered the historical habitat of Cliff Swallows. This swallow population has been observed to take advantage of human constructed structures such as highway overpasses, bridges and buildings for nesting areas. What repercussions do Cliff Swallows face when having to adapt away from their standard and natural nesting areas?

A 2021 article by Lauryn Benedict et al. published in The Journal of Ornithology studied the affect urbanization had on the presence of an ectoparasite, commonly known as the “swallow bug” (Oeciacus vicarius), found in the nests of Cliff Swallows. Swallow bugs severely impact Cliff Swallows as they are associated with nesting failures and shortening lifespans by making the swallows more susceptible to viruses.They hypothesized that swallow bug populations would increase in highly urban areas because of the elevated presence of the invasive House Sparrow in cities. House Sparrows are another host to swallow bugs. They take over Cliff Swallow nests throughout the year, especially when the swallows migrate south.

With higher parasite numbers in urban areas, why would the Cliff Swallows continue choosing to habitate in human-altered areas? While living among a parasite infestation might seem unlivable for you and I, for the Cliff Swallows, this cost does not seem to outweigh the benefits of forming large colonies at urban sites. As the researchers suggest, benefits might include street lights attracting insects for easier foraging, provide protection from predators and concrete providing ideal adhesion for mud-nests. Further research into these, among many other factors, are suggested by Benedict et al. to help explain why Cliff Swallows continue to nest in large and highly parasitized colonies.

Cited Literature

• All About Birds. Retreived October 30, 2022, from https://www.allaboutbirds.org/guide/Cliff_Swallow/id
• Audubon. (2022, April 1). Cliff Swallow. Retrieved October 30, 2022, from https://www.audubon.org/field-guide/bird/cliff-swallow
• Benedict, L., Covy, N.E., Love, P.A., & Stier, S.T. (2021). Human presence outweighs non‑anthropogenic factors as a driver of avian nest parasite loads. Journal of Ornithology, 162(1), 155-164. https://doi.org/10.1007/s10336-020-01810-8
• BirdLife International. (2022). Petrochelidon pyrrhonota. Retrieved November 3, 2022, from http://datazone.birdlife.org/species/factsheet/cliff-swallow-petrochelidon-pyrrhonota
• Brown, C.R., & Brown, M.B. (1997). Coloniality in the cliff swallow. The effect of group size on social behavior. International Journal for Parasitology, 27(4), 453. https://doi.org/10.1016/S0020-7519(96)00194-4
• Cliff Swallow Project. Retreived October 30, 2022 from https://www.cliffswallow.org/introduction.html
• Gauthier, M., & Thomas, D.W. (1993). Nest selection and cost of nest building by Cliff Swallows (Hirundo pyrrhonota). Canadian Journal of Zoology, 71(6), 1120-1123. https://doi-org.ezproxy.viu.ca/10.1139/z93-152
• Government of Canada. (2015, August 19). Cliff Swallow (Petrochelidon pyrrhonota). Retrieved October 30, 2022, from https://wildlife-species.canada.ca/bird-status/oiseau-bird-eng.aspx?sY=2019&sL=e&sM=c&sB=CLSW
• Hallmann, C.A., Foppen, R.P.B., van Turnhout, C.A.M., de Kroon, H., & Jongejans, E. (2014). Declines in insectivorus birds are associated with high neonicotinoid concentrations. Nature, 511, 341-343. https://doi.org/10.1038/nature13531
• Leasure, D.R., Kannan, R. & James, D.A. (2010). House Sparrows associated with reduced cliff swallow nesting success. The Wilson Journal of Ornithology, 122(1), 135-138.
• Loesche, P., Beecher, M.D., & Stoddard, P.K. (1992). Perception of Cliff Swallow Calls by Birds (Hirundo pyrrhonota and Sturnus vulgaris) and Humans (Homo sapiens). Journal of Comparative Psychology, 106(3), 239-247.
• Sibley, D.A. (2016). Sibley Birds West. Knopf.
• Smith, A.C., M-A.R. Hudson, C.M. Downes, and C.M. Francis. (2015). Change points in the population trends of aerial-insectivorous birds in North America: Synchronized in time across species and regions. PLOS ONE, 10(7).