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Monitoring Barn Swallow Nests

Why Monitor Barn Swallow Nests?

Reports on nesting activity tell us where and when breeding is occurring, and how successfully Barn Swallows are producing young. This information helps us determine what factors may be contributing to the population decline.

How to Find Barn Swallow Nests

Barn Swallows nest in and around barns, sheds, and boathouses; under bridges; and in culverts. Nests are often adhered to vertical surfaces near the ceiling, or under eaves on the outside of buildings. Barn Swallows also build nests on horizontal beams, or on top of ledges, light fixtures, cables, etc. which provide additional support for the nest.

To find nests in a barn or shed, use a flashlight to scan rafters and other areas near the ceiling that could be used to support a nest. In two-storey barns, the majority of nests are usually found in the lower level.

PLEASE NOTE: Permission from property owners must be obtained before searching for nests on private property.

IMPORTANT: If you are interested in monitoring Barn Swallows using the BSC Project NestWatch protocol, please contact to obtain a copy of the Canadian Wildlife Service Scientific Permit from Bird Studies Canada.

Cliff Swallow at nest (Photo: Mark Peck)

Cliff Swallows

You may find Cliff Swallow nests near Barn Swallow nests. Cliff Swallow nests are easily identified by their shape, which is rounded and enclosed except for a small tunnel entrance. Cliff Swallows sometimes take over Barn Swallow nests by building domes on top of them, even if they are occupied.

When to Check Barn Swallow Nests

Barn Swallow colonies should not be disturbed too early in the nesting season. The risk of nest abandonment is higher during the early stages of nest building and laying. Start checking nests when you think the birds have begun incubation (usually late May in southern Ontario).

Do not check nests too early in the morning or in inclement weather when eggs and young are more vulnerable to exposure. Avoid disturbing nests when it is cold or during heavy rain, when birds may already be stressed due to reduced foraging ability and/or insect availability.

How to Check Barn Swallow Nests

Because Barn Swallow nests are usually very close to the ceiling, roof, or overhang of a structure, it is often impossible to observe nest contents from above. Use the methods described below to check nests at different stages of development.

Nests with eggs
(Mirror on a pole)

Nests containing eggs can be checked using a mirror on a pole and a flashlight. Fasten a mirror (e.g., an adjustable bike mirror) onto a long or extendable pole. Position the mirror above the nest. Use a small, bright flashlight to light the mirror. (Practice using the mirror elsewhere before trying this technique, to avoid accidentally hitting the nest!) You may not always be able to determine an accurate number of eggs (e.g. a feather may be blocking your view). Record the number as a minimum count if visibility of the contents is obscured.

Nests with young
(Remote observation)

Once eggs have hatched, do not check the nest using a mirror on a pole. To minimize the risk of harming the young, or causing them to fledge prematurely, monitor nests with young from a distance. Watch adults for clues (e.g., carrying food to the nest, carrying fecal sacs away from the nest). As the young get older you may be able to see them from a distance, especially with binoculars. Try to count the number of heads you see. Some nests may be difficult to observe, and some young may not be visible, so just do your best!

NOTE: Please use extreme caution with the mirror and do not touch the nest! Nests can be fragile, and may fall if disturbed. For nests that are more than 12 feet above the ground, do not attempt to use a mirror on a pole - use your observational skills to gather information about these nests from a distance.

Clues about Nesting Stage

Gather information about nesting stage by watching the adults and looking for other clues around the nest. Keep in mind that if the adults are disturbed by your presence, they may leave the nest during any stage. Here are some clues to look for:

  • An adult sitting on the nest usually indicates incubation or newly hatched young (brooding).
  • After young hatch, you may see eggshells on the ground.
  • As nestlings get older, both adults will be busy feeding the young, and you may observe a pile of fecal material underneath the nest.
Watch Out! Barn Swallow young may fledge prematurely if startled when they are close to fledging. Do not approach a nest if you can see well feathered young from a distance.
See instructions on what to do if young fledge prematurely

Labeling Nests

If you are monitoring more than one nest, it is very important to label the nests. In a barn, consider affixing a small piece of flagging tape below each nest using tacks. Write a number, or nest code, on the flagging tape in permanent marker to keep track of your nests even if there are changes in the colony throughout the season (e.g., new nests being built).

How Often to Visit a Nest

Check Barn Swallow nests every 5-7 days throughout the entire nesting attempt (i.e., from the first visit until the nest fledges or fails). Do not visit more frequently, as this could have a negative impact on Barn Swallow nesting success. The recommended frequency of nest visits is less often than for other species because there is some indication that more frequent visits may negatively impact nesting success for Barn Swallows. After the nesting attempt is complete, check the nest one last time to see if any unhatched eggs remain. If you find a Barn Swallow colony, try to monitor all the active nests throughout the breeding season. Remember that some pairs of Barn Swallows raise two broods. Please submit your data even if you only visit a nest or colony once over the season.

More on the Information you're collecting

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Minimizing Disturbance

  1. Always move slowly and carefully around nests;
  2. When using a mirror to check nests, do not touch the nest;
  3. Do not handle the eggs or young;
  4. Do not approach within about 5m of nests with visible young;
  5. Minimize your time at the nest;
  6. Do not spend more than an hour checking nests in a colony (half an hour in cooler weather or rainy conditions);
  7. Minimize the number of photos taken.

Nest Failure

Barn Swallow nest that has been taken over by a Cliff Swallow (Photo: Mike Cadman, Canadian Wildlife Service

Although Barn Swallows have a high rate of nesting success, nest failures (i.e., no young surviving to the stage of fledging) can occur for a number of reasons. If all the eggs disappear, or the young are gone before they should have fledged, you'll know the nest has failed. Possible causes include:

  • Predation
    Barn cats, rats, mice, owls, and raptors are all possible predators. Rats and mice are more likely to predate nests with eggs. Cats, owls, and raptors may take all the young from a nest, leaving no trace.
  • Nest destruction by other species
    House Sparrows and Cliff Swallows are known to occasionally take over Barn Swallow nests, sometimes destroying eggs in the process. House Sparrows may also take over nests with young, destroying nestlings.
  • Ectoparasites
    Barn Swallow young are often affected by mites and blowflies. Severe infestations can lead to partial or complete nest failure.
  • Human causes
    Because Barn Swallows nest in close proximity with humans, nests may fail due to intentional disturbance or destruction, or unintentional disturbance from human activities near the nest.

Please submit data on all nests you monitor, even if they do not succeed, or the final outcome is unknown.

If a nest you are monitoring fails, make note of the conditions of the nest and if any contents remain (e.g., broken eggshells), as this may provide clues about the reason for nest failure.

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