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Bay Area Birds: Help local birds with nesting boxes

By Charlie Frisk

We are now in the peak of nesting season for many species of birds, and if you have nesting boxes up in your yard, hopefully one or more of them are occupied.

Most of the birds that use nesting boxes are cavity nesters, meaning they nest in hollow cavities in trees.

The cavity nesters that are most likely to use nest boxes are those that are not capable of excavating their own cavities, such as house wrens or chickadees.

Raptors like screech owls and kestrels will also use nesting boxes, as well as hooded mergansers and wood ducks.

For many years, we have had both house wrens and chickadees utilize nesting boxes in our yard.

Chickadees typically start nesting a little earlier than house wrens, so some years a box has been used first by the chickadees and then, once their young have fledged, by the wrens.

One species that definitely benefits from nesting boxes is the purple martin, which is thought to nest almost exclusively in human-made nesting boxes.

Native Americans have hung dried gourds with holes drilled in them for martins to use for hundreds of years.

The purple martin, which has seen a decline in its population, has become so accustomed to using human-made housing that they prefer to nest in houses within view of human habitation.

The most major threats to their species include pesticides, particularly the newer neonicotinoid insecticides, and competition for nesting sites from invasive house sparrows and European starlings.

However, providing housing for purple martins is not for the casual nest box provider. Their requirements are very specific and require a dedicated builder and continual monitoring and maintenance, or you will do more harm than good.

Purple martins are colonial nesters, so providing housing for multiple pairs of birds is a must.

They are also quite claustrophobic, so nesting boxes or gourds must be at least 60 feet, but preferably 100 feet from trees or buildings.

Ideally, the location should be within a half mile of a water source, such as a stream or lake.

If you have house sparrows or European starlings in your neighborhood, they will usurp the nest boxes and continually harass the martins, so you need to be prepared to deal with them.

House sparrows and European starlings are considered harmful, invasive species.

A good source for information on establishing purple martin nesting sites is the Purple Martin Conservation Association at purplemartin.org.

Eastern bluebird
Another species that benefits from human-provided nest sites is the Eastern bluebird, but they are also not a species for the casual nest box provider.

The Eastern bluebird population has also declined dramatically because of insecticide use and house sparrows and European starlings.

In order to be successful, bluebird houses require a fairly specific habitat and must be continually monitored to remove the house sparrow nests that will inevitably be built within.

Other, less picky species such as house wrens, chickadees and tree swallows will also compete for the nest boxes.

Because of the knowledge base and the continual maintenance and monitoring necessary to be successful with Eastern bluebird nest boxes, I strongly urge you to join the Bluebird Restoration Association of Wisconsin if you are considering providing nest boxes for bluebirds.

They are a great support group for nest box providers and a source for all of the information you will need to be successful.

More information can be found at braw.org.

Black-capped chickadees are cavity nesters, meaning they nest in hollow cavities in trees. Sue Ascher Photos

Many people think the wood duck is unique among ducks in utilizing nesting houses, but there are actually many other duck species that will also nest in houses.

Goldeneyes, buffleheads and hooded and common mergansers are cavity nesters and will use nesting boxes.

Duck boxes are most effective if they are installed over water because there will be fewer problems with predators, such as raccoons and squirrels.

I put them up in the winter when the ice is frozen by drilling a hole in the ice with an auger, and then driving a 10-foot steel pipe into the bottom of the pond.

Tips for putting up birdhouses
• Beginners should start out simple.

The least complicated species to attract to birdhouses are house wrens and chickadees.

• Build the houses to the correct dimensions and with the proper hole sizes.

The hole size is extremely important for keeping out pest species, such as house sparrows, starlings and raccoons.

• Do not put a perch on the house.

The birds using the house gain no advantage from a perch, and it will provide a roost for house sparrows and starlings to harass the occupants and work on enlarging the hole.

• Design the house so it can be opened and cleaned once the young have fledged.

• Take down the houses when the nesting season is over.

Houses left up all winter are frequently damaged by squirrels and mice gnawing on them.

• Houses hung from branches or put on poles generally attract more birds than houses attached to tree trunks.

Those placed on tree trunks frequently attract squirrels and raccoons.

At the end of the day, regardless of what kind of nesting box you install or set up, birdhouses can provide a lot of entertainment for homeowners.

Happy birding.

Bay Area Birds is a monthly column written by local ornithology enthusiast Charlie Frisk.

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