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Nestbox Monitoring: Why and How

Drs. Foster & Smith Educational Staff
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The Nestbox Close Up
Cavity-nesting birds depend heavily upon man-made nestboxes these days. The reasons are many, but among them is increased competition The Nestbox Close Up
for natural cavities. The introduction of aggressive non-native species such as house sparrows and starlings as well as urban sprawl and development have reduced the number of available natural cavities.
The Nestbox Close Up

Our growing interest in the use of nestboxes helps seasonal species like bluebirds, purple martins, wrens, and tree swallows tremendously. However, if we place a man-made nestbox, there are many reasons we need to monitor and maintain it, especially during nesting season.

How do you monitor the nest box?
There are many ways to monitor nest boxes. Many of the newer nest boxes include a side panel that swings open for checking on the inhabitants. Some people use a telescoping mirror to look into nests without disturbing them. Others install a camera near the box before nesting season, or install one close to the entrance hole, to get real images of nest activities. These cameras are a great way to view all of the early social and feeding behaviors. You will learn amazing things about wild birds, without being the least bit invasive. We really recommend this approach.

Why should you monitor nestboxes?
There are several reasons why you should monitor your nestboxes during the nesting season.

  • Rotted or damaged wood on the nestbox can leave the eggs vulnerable to the elements like rain or direct sun.
  • Chewed entrance holes increase the likelihood that larger species like starlings, house sparrows or other predators could access the nest and attack and destroy eggs or nestlings.
  • Many other creatures can invade or inhabit the nest, including wasps, fire ants, snakes, raccoons, and mice.

Each of the above circumstances minimizes the likelihood of successful nesting in your nestboxes, and sometimes in your entire yard.

Will birds abandon a monitored nestbox?
Most cavity nesting birds will be protective of the nest but will not abandon it if monitored. You have to be quiet, quick and respectful with your monitoring visits, however, to minimize the stress on the birds. Nesting time is stressful enough, with the added demands of feeding and defending territory. On the other hand, you don't want the adults to become so accustomed to your visits that they begin to be less protective of the nest; this will be detrimental when a real threat to the nest comes along.

You do, however, want to avoid handling the eggs or nestlings in the nest, and you want to avoid monitoring altogether when the nestlings are getting ready to fledge (11-14 days old). Your intrusion at this stage could cause them to fledge the nest prematurely, before they are able to fly or find food for themselves.

How frequently should you monitor? And when is best?
During nesting season, it's a good idea to monitor the nest at least once or twice a week. When the last clutch leaves the box for the summer, remove all nests and clean the box out well. You won't have to monitor again until the next nesting season.

The best time to monitor the nest is in the afternoon. Avoid the morning hours, since most females lay their eggs in the morning. And, eggs and nestlings get cold easily if left alone in the morning. Also, avoid after dusk hours when the female is likely to return to the nest for the night.

Make note of the first few days of incubation. During this time, approach the nest only when the female leaves the nest. If you approach the nest and are not sure whether the female is absent, give a gentle knock or two on the nest and stay away from the entrance hole so the female can fly out safely. If the female doesn't leave the nest before you look in, do not force her off the nest, and keep your observation brief.

Bird Guardian Birdhouse Predator ProtectorWhat are you looking for when you monitor?
When you monitor, you're looking for evidence of anything that could disturb or harm the native bird population's chances of successfully nesting in the box. It is illegal to move or disturb the nest of any native birds, but if you see non-native species like house sparrow or starling nests in the box, you can legally remove their nests, eggs, and young. So, it's important to be able to identify the eggs and nests of different species.

You're also looking for evidence of occupation of animals or insects other than native birds, such as wasps, snakes, spiders, flying squirrels - any creature that may be occupying the box at the expense of native birds. You want to carefully remove these species and clean and re-hang the box as soon as possible. Also, look for evidence of chewing around the entrance hole that could enlarge the entrance for predator species. Add a predator guard to prevent this. You should also monitor for damage to the box that would allow rain to come into the nest.

If you see eggs of native birds, check back frequently to note the hatch day. This will help you avoid the nest during those critical days before the nestlings fledge. If you see any dead birds, remove them and dispose of them safely.


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