Door To Nature: Nest Boxes for Birds

Many nest boxes for birds can be found along some back roads in Door County. You may wonder what species use them. The smaller cavity nesters are typically chickadees, tree swallows, eastern bluebirds and house wrens.

Many other species nest in cavities or holes in trees, like woodpeckers, eastern screech owls, American kestrels, great crested flycatchers and even some ducks, like the common goldeneye, wood duck and common merganser. The size of the entrance hole determines which birds can nest in a box or tree opening.

If you set up a nest box on your property but cannot open and clean it, how do you know what’s going on inside? Some people think they’re helping birds by putting out a nest box, but if they don’t monitor its use, their efforts may be for naught. Old nesting material in the box may remain there for years, with no other bird using it.

I volunteer as the Door County coordinator of nest-box monitors for the non-profit organization Bluebird Restoration Association of Wisconsin. That group was formed with encouragement from the Wisconsin Department of Natural Resources (DNR) in the mid-1980s to increase eastern bluebirds’ reproductive success. Our Door County group is made up of about 22 monitors. 

Non-native birds like European starlings and house sparrows were occupying nest holes, limiting access for bluebirds. Our group began building nest boxes and doing weekly monitoring to document how well bluebirds were producing young that could safely fledge from the box. Several nest box styles were compared to find out which were the most beneficial to the bluebirds.

We use a simple top-opening nest box on our bluebird trail, originally called the K-style or Kentucky box. This style makes it easy to see what’s in the nest quickly, then close the box and walk away. Some people wonder if opening the box every week to monitor it disturbs the birds, but they come back very soon after we leave.

A female bird is extremely faithful to her nest. It’s the only thing she has, and the instinct to incubate her eggs and get them to hatch is ingrained in her. These birds only have a few months out of the entire year to procreate.

When we do our weekly monitoring, I make note of what we find, such as started or completed nests, what species of bird is occupying the box, how many eggs have been laid and when they are incubated.

The hen will stay on the eggs and keep them warm for about 14 to 15 days, leaving the box briefly to find food. We note the approximate date when eggs hatch so we can estimate the date the young will fledge and leave the box. If there is good insect food for the adults to feed to the chicks, the young can grow and exit the box in about 15 to 17 days.

Once they’re gone, we can clean out old nesting material so the female bluebird can build a new nest. The male helps the youngsters learn how to find food as they live in the trees and strengthen their wings.

Tree swallows have only one brood. Once the young have left the nest, they are gone for good and we clean out the box. If it’s early enough in the summer, another species, like a bluebird, might move in.

Tree swallows get all their food in the air and can fly up to four miles away from their nest, while bluebirds get their food on the ground and need lots of space for hunting. That’s why we don’t place nest boxes close together. They need to be at least 125 yards apart, depending on the quality of the habitat.

When an area becomes overgrown with shrubs, it encourages house wrens to move in, and they are not good neighbors for bluebirds.  The male wren often fills every box with twigs until a female arrives to decide which one she wants. 

We then remove the box and try to find a better location. We also must protect the box from predators like raccoons, squirrels, snakes, feral cats, opossums and anything else that might eat the eggs or young.

When bluebird chicks fly out of the box, they must go to a nearby tree. Then the adults help feed them as they exercise their wings and become stronger. If a baby bluebird lands on the ground, it might not have the ability to fly up to a tree – then, it is doomed.

The openings of tree-swallow boxes don’t need to face nearby trees; the young are out and flying right away with the adults. Placing a nest box requires a lot of thought and care for the occupants to succeed.