All About Swallow Roosts
Millions of swallows migrate from South America, Mexico and the Caribbean to Canada every spring to raise their families. They can travel up to 320km every day during migration! Species such as the Purple Martin, Barn Swallow and Bank Swallow are just some of the birds that call Canada their summer home and breeding grounds.
Swallows are aerial insectivores, which means their diets are almost solely made up of flying insects. Unfortunately, as insect populations decline globally due to pesticide use and climate change swallows are becoming more and more threatened. In fact, some swallow species such as the Purple Martin are not currently protected or listed under the Canadian Species at Risk Act (SARA) even though they have lost over 50% of their population nationally and over 90% east of Saskatchewan.1,2
Swallow Roost 101
After their respective breeding seasons have finished in Canada, most of the swallows migrate a short distance to areas where they congregate together to rest at night in a safe location that is relatively near sources of flying insects. This congregation of many diverse swallow species is known as a post-breeding swallow roost. These nocturnal roosts tend to be found in wetlands such as marshes and swamps, (though smaller roosts can also be found in fields of tall crops like corn or Sugar Cane) and may have a variety of benefits for the swallows found within them.
These post-breeding roosts appear to be a stage in the annual cycle of each species that is critical to their survival, in part because it prepares them for their epic migrations to their wintering grounds in South and Central America, Mexico and the Caribbean. It is likely that non-breeding swallow roosts provide security and safety due to the sheer number of swallows within them providing safety from predators and securing an abundance of prey.
Of the seven swallow species found within Canada, only the Tree Swallow regularly overwinters in North America. Five of the species migrate to South America to balance their non-breeding season. However, both the Tree Swallow (Tachycineta bicolor), Purple Martin (Progne subis), Barn Swallow (Hirundo rustica), and Bank Swallow (Riparia riparia) all have been observed demonstrating nocturnal post-breeding roosting behaviour in Canada.3, 4, 5, 6
Generally speaking, swallows tend to migrate North to Canada in April and May, breed in June or July and begin roosting in August after their breeding stage has been completed. You can learn more about the Purple Martins migration journey through our online, interactive StoryMap. Their migration to their respective overwintering locations tends to occur between September and November, this period may also include roosting behaviour depending on the species. Once April rolls around again the migration, breeding, and roosting journey starts all over!
Why Are Roosts Important to Protect?
Non-breeding swallow roosts can provide a host of benefits for the vulnerable swallow species found within them. Avoiding predation and ectoparasites as well as exchanging information, and taking advantage of finding prey together are just a few of the benefits of post-breeding, communal roosting.7, 8 The most important perk of non-breeding swallow roosts however is that they allow thousands of swallows to rest and gain valuable energy resources that they require to continue their migrations to their overwintering locations in the fall. Swallow roosts can change location from year to year. Most interestingly, these relatively unknown non-breeding swallow roosts sites can be spotted on weather radar.
Swallow roosts are ephemeral in nature and only last for about a month. However, in that short time, numerous swallows can gather together in relatively small geographic spaces. Hundreds to hundreds of thousands of swallows can settle in one roost site to take advantage of nearby food due to safety in numbers. Large enough roosts can also be detected by weather radar, as can be seen below. One of Nature Canada’s own staff members spotted the
“donut” or “croissant” shape on radar imagery and inferred that it may be demonstrating a possible roost site. They were correct! When swallows depart from a roost site in the early hours of the morning, a radar monitor used with adequate training can help to easily identify the distinct “donut” or “croissant” shaped image that appears on weather radar images.
It is critical that we protect these roost sites as they are crucial stopover and resting sites for various vulnerable and endangered swallow species that allow them to recharge before continuing to their overwintering locations. Non-breeding nocturnal roost sites may be critical habitats that allow for a successful migration journey for many swallow species in Canada. Without these non-breeding, nocturnal roost sites the numerous benefits they provide to swallow populations will potentially be lost. The loss of roosting sites may result in even larger swallow population declines nationally and as well as cascading irreversible changes to Canada’s vulnerable ecosystems and biodiversity.
Roost Monitoring & Reports
Are you interested in learning more about the non-breeding swallow roost sites found in Ontario or the species found within them? Nature Canada has carried out multiple years of non-breeding roost monitoring and research. You can find our own roost monitoring data and reports here: 2018, 2019.
If you are interested in learning more about some of the spectacular species that can be found in non-breeding swallow roosts check out the reports and blog posts below:
- Purple Martin
- Barn Swallow
- Bank Swallow
- Tree Swallow
- Cliff Swallow
- Northern Rough-winged swallow
- Violet-green Swallow
2Falconer, M., & Badzinski, D. (2013). COSEWIC. 2013. COSEWIC assessment and status report on the Bank Swallow Riparia riparia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. ix + 48 pp. (www.registrelep-sararegistry.gc.ca/default_e.cfm).
3Brown, C. R. and S. Tarof (2020). Purple Martin (Progne subis), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.purmar.01
4Brown, M. B. and C. R. Brown (2020). Barn Swallow (Hirundo rustica), version 1.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.barswa.01
5David W. Winkler, Kelly K. Hallinger, Daniel R. Ardia, R. J. Robertson, B. J. Stutchbury, and R. R. Cohen Version: 1.0 — Published March 4, 2020
6Garrison, B. A. and A. Turner (2020). Bank Swallow (Riparia riparia), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.banswa.01
7Paquet, M., Doutrelant, C., Loubon, M., Theron, F., Rat, M. and Covas, R. (2016), Communal roosting, thermoregulatory benefits and breeding group size predictability in cooperatively breeding sociable weavers. J Avian Biol, 47: 749-755. https://doi.org/10.1111/jav.00916
8Eisere, L. (1984). Communal Roosting in Birds. Bird Behavior, Volume 5, Numbers 2-3, 1984, pp. 61-80(20).