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How to Monitor a Nest

Once you have located a nest, follow these steps:

  1. Determine what species the nest belongs to;
  2. Record the location of the nest;
  3. Monitor the nest every 3-5 days until the nesting attempt is complete;
  4. Check the nest after young have left to look for unhatched eggs or dead young.
WARNING! Before approaching any bird nest, it is best to observe nesting activity from a distance. If you find a nest during the nest building stage, wait until your next visit to check the nest. Nest abandonment is higher during the early stages of building and laying therefore you should not approach the nest until you think incubation has begun.

1) Determine the species

If you do not know what species the nest belongs to, you can use field guides to help identify the parents and you can also get clues from the nest. If you're still uncertain, send us a photograph of the bird and/or nest and we can help you identify the species. Please only submit data on nests for which you can confidently identify the species.

2) Record the location of the nest

Choose a reference point near the nest (but at least 10 m away) that will be easy to locate and remember (e.g., a large tree, shed, gate, etc.). Make a sketch in your field notebook from the reference point noting the distance and direction to the nest. You'll also want to approximate the height of the nest and note what type of tree, shrub, or other substrate it is in.

Never put flagging tape or any marking material close to a nest. This could attract predators. If you do need to mark a nest in the field, place a small piece of flagging tape at least 5-10 m away and record the location of the nest from the flagging tape in your field notebook or on your data sheet. Make sure to take detailed notes on nest location; it can sometimes be challenging to re-locate nests as they become more hidden by foliage later in the season.

3) Monitor your nest every 3-5 days

Visits throughout the entire nesting attempt are very useful because each period provides different information (e.g., clutch size, brood size, nest outcome, etc.). If you cannot check the nest every 3-5 days, try to check it two or more times with visits spaced about a week apart. If you only visit a nest once, please still enter the data. Single nest visits can contribute valuable information to the distribution or nesting chronology of a species.

Note that you should not check a nest more often than every 3-5 days, to minimize disturbance to nesting birds.

4) Check the nest after the nesting attempt is complete

Sometimes there are unhatched eggs or dead young left in a nest after it has fledged. It is important to try to gather this information by checking the nest after the young have left.

Note: Make sure that you report all nests that you monitor, even if they fail (i.e., no young fledge), or if the final outcome is unknown.

Tips and information about nest monitoring

How to check high nests

Nests are often a few metres above ground, making it challenging to check the contents without special equipment.

  • Stepladder
    If the nest is not too high up (about 1.5 m) you can use a stepladder to check the contents, as long as it is safe to do so. Be very careful not to disturb the nest or nest support when you are setting up the stepladder.
  • Mirror and golf ball retriever pole
    This extendable pole was originally designed to retrieve golf balls from ponds and creeks and should be available in many golf shops. Combined with a small mirror, these two items will allow you to check nest contents 5 m up in a tree without ever leaving the ground. Tape the mirror into the ball basket and then bend the basket to a 75° angle. To check a nest, extend the pole above the nest and look in the mirror. Practice using this tool before checking an active nest so that you can safely maneuver the mirror without touching the nest and causing accidental damage or harm to the eggs or young.
  • Bicycle mirror (with mounts) and wooden pole
    Similar to the previous device, a bicycle mirror with mounts can be fastened onto a wooden pole. Bring the wooden pole above the nest and look into the mirror to check the nest contents. Again, make sure that you can safely maneuver this equipment before using it to check an active nest.

Note that if you are using equipment to check a nest, such as a mirror on a pole or a stepladder, it is often helpful for ease of data recording and for safety, to have another person assist with the nest check.

How to check nest boxes

Nest boxes should be designed so that one of the panels can be opened to check nest contents. Before opening the panel or looking through the opening, give a few gentle taps on the box, so the adult can exit. This reduces the risk that the bird will damage the eggs or crush the young upon leaving. Eastern Bluebird and Tree Swallow nest boxes on roadsides or public property are often monitored by dedicated volunteers. Before checking any nest boxes that do not belong to you, make sure you get permission from the owner.

What information are you collecting and why?

Monitoring nesting activity allows us to gather important information about where and when breeding occurs, and how successfully birds are producing young. This information can help determine the health of bird populations, and highlight changes that may be occurring in the nesting success, breeding biology, or distribution of a species.

When you are monitoring a nest, there are several important pieces of data that you are trying to collect including:

  • Clutch size
  • Brood size
  • Key dates (e.g., hatch date, fledge date)
  • Nest outcome (did it fledge or fail?)
  • How many young fledged?

Although it may be difficult to gather all of the above information for each nest, data gathered from multiple nests and observers helps tell the full nesting story for a species and track changes over time.

Nest monitoring - key terms
Clutch sizeThe number of eggs a female lays in a single nesting attempt
Brood size The number of birds hatched from a single clutch of eggs
Altricial young Birds that are naked, blind, and helpless when they hatch (e.g., most songbirds)
Precocial young Birds that are fully feathered, mobile, and active when they hatch (e.g., ducks, geese, shorebirds)
Incubation periodThe length of time the clutch is incubated
Hatch dateThe day the young hatch (may occur over a couple of days)
Nestling period The length of time the young remain in the nest
Fledge dateThe day the young leave the nest (may occur over a couple of days)

Nest parasitism by Brown-headed Cowbirds

Learn more about Brown-headed Cowbirds
Yellow Warbler nest with a Brown-headed Cowbird egg (Photo: Darrin O'Brien)

Brown-headed Cowbirds do not build nests or raise young. Instead, they lay eggs in other birds' nests. Cowbird young are then raised by other species, often to the detriment of the species' own young. The Brown-headed Cowbird is the most common parasitic bird species in North America and has been found to lay its eggs in nests of more than 200 species. If you find a Brown-headed Cowbird egg in a nest, please do not remove it. Continue to monitor the parasitized nest to determine the fate of the host eggs as well as the Brown-headed Cowbird egg(s).

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