Across North America, our adult breeding bird population has declined by 29% since 1970. That is more than 1 in 4 birds—nearly 3 billion birds—gone in less than a single lifetime. Bird populations are declining not just in rare or endangered species but even among common backyard birds.

Threats include urban sprawl, climate change, pesticides, a lack of dead trees called snags for nesting, and a lack of native plants to host insect larvae and provide berries in winters. This habitat loss and degradation has made it harder for birds to find the essential food, water, shelter, and nesting sites. In addition to habitat loss, birds are killed by cats, invasive house sparrows, and collisions with buildings, automobiles, and other manmade features. 

Estimates of annual bird deaths from specific human-related causes (other than habitat loss) in the United States and Canada. Source: Loss et al. 2015. It should say 2.4 billion from cats.

Nest boxes provide alternative nesting sites to increase the odds that native birds successfully breed. Using guards, poles, and weekly monitoring, we minimize predators and can prevent and treat pests and invasive competitors. Predator guards minimize the chance that snakes, squirrels, raccoons, large birds, and cats will prey on the eggs and nestlings.  Monitors also look for signs of invasive House Sparrows nesting, ants, blowflies, and wasps and use remedies to discourage them.

Studies have shown that over 90% of bluebirds successfully fledge in monitored nest boxes mounted on pipes with predator guards – as compared to only 65% in natural cavities. So our work improves their odds by almost 50%.

In Arlington County, almost 800 native birds have fledged from nest boxes on our trails since 2008. They include Eastern Bluebirds, Chickadees, House Wren, and Tree Swallows.

In the winter, downy woodpeckers often use the nest boxes to stay warm when resting or when sleeping at night (brooding).

The above six bird photos were taken in Arlington County and contributed by David Howell, ARMN Class of 2018.

Bluebird egg and nestling photo © Alison Davis-Holland, ARMN Class of 2008.