Skip to main content

Bridge Construction May Still Be Taking Toll on Swallows

Support Provided By
cliff-swallow-petaluma-5-15-14-thumb-600x399-74070
Cliff swallow in flight | Photo: Don DeBold/Flickr/Creative Commons License

A legal settlement in January between Caltrans and wildlife protection groups over a highway construction project in Sonoma County may have protected local nesting birds in the short term, but the alternative measures used may be affecting wildlife populations in the long term, according to an environmental attorney who works with the Golden Gate Audubon Society.

At issue are cliff swallows, which had long built their mud nests on a pair of concrete bridges near Highway 101 in the Sonoma County community of Petaluma. When Caltrans decided it was time to rebuild those bridges during a highway widening project, contractors installed bird netting to keep the swallows away from the construction area. But that netting ended up snaring the small birds, and more than a hundred of them died.

After five wildlife groups sued in May 2013 to get rid of the netting, Caltrans agreed in January to use other means to deter the swallows, including artificial surfaces to which the mud nests wouldn't adhere. But as April Rose Sommer writes on the Golden Gate Audubon Society's blog, that lesser evil may have long-term effects on the historic Petaluma River swallow colonies.

Cliff swallows are so-named for their habit of building mud nests in cavities on cliffs and protected rock outcroppings. They're one of the wildlife species that has adjusted well to human influence, mainly because of our habit of building thousands of vertical "cliff faces" everywhere we go. Concrete bridges and similar structures are especially attractive to the swallows because they tend to have concrete sills that overhang the vertical faces, which allow the birds to build their nests more efficiently.

When Caltrans agreed to end the use of netting during the construction project, its contractor C.C. Myers deployed a slick material called "Bird Slide" over the concrete. When the swallows learn after a few tries that they can't get their carefully gathered beaks full of mud to stick to the Bird Slide, they give up and build their nests somewhere else.

That's undeniably a better alternative than the netting: rather than getting injured or killed through entanglement, the birds shrug their shoulders and go off to build a nest somewhere else. And they may not have to travel far: C.C. Myers has left some of the concrete on the bridges bare, where swallow nests won't get in the way of construction.

But according to Sommers, those patches of open concrete are more exposed to the elements than is ideal for the longevity of the nests, which are, after all, made of mud and spit. Swallows have nested on the bridges this season, with about 80 nests total. But that's well under the historic 500-800 nests the bridge colonies built before construction.

Where did the remaining swallows go? They may well have dispersed throughout the nearby community looking for more suitable nesting sites. And that's a problem: the highly gregarious birds fare better in huge colonies with up to 6,000 nests. Breaking up a colony may well mean a population decline in the long run.

"This seems to be what happened with Mission San Juan Capistrano's famous swallow colony," writes Sommers, "[which] has dwindled ever since nests were removed and excluded during preservation efforts in the early 1990s."

Sometimes there just isn't such a thing as a quick fix, it would seem. Sommers says that Golden Gate Audubon will be monitoring the success of the Petaluma River swallows in hopes that the local decline will be temporary.

Support Provided By
Read More
Gray industrial towers and stacks rise up from behind the pitched roofs of warehouse buildings against a gray-blue sky, with a row of yellow-gold barrels with black lids lined up in the foreground to the right of a portable toilet.

California Isn't on Track To Meet Its Climate Change Mandates. It's Not Even Close.

According to the annual California Green Innovation Index released by Next 10 last week, California is off track from meeting its climate goals for the year 2030, as well as reaching carbon neutrality by 2045.
A row of cows stands in individual cages along a line of light-colored enclosures, placed along a dirt path under a blue sky dotted with white puffy clouds.

A Battle Is Underway Over California’s Lucrative Dairy Biogas Market

California is considering changes to a program that has incentivized dairy biogas, to transform methane emissions into a source of natural gas. Neighbors are pushing for an end to the subsidies because of its impact on air quality and possible water pollution.
A Black woman with long, black brains wears a black Chicago Bulls windbreaker jacket with red and white stripes as she stands at the top of a short staircase in a housing complex and rests her left hand on the metal railing. She smiles slightly while looking directly at the camera.

Los Angeles County Is Testing AI's Ability To Prevent Homelessness

In order to prevent people from becoming homeless before it happens, Los Angeles County officials are using artificial intelligence (AI) technology to predict who in the county is most likely to lose their housing. They would then step in to help those people with their rent, utility bills, car payments and more so they don't become unhoused.