Why Are Sea Gulls Suddenly Flocking To The Highland Park Bridge?

May 22, 2017

The Highland Park Bridge is noisy—traffic speeds by as barges pass through the nearby lock and a train rattles underneath. But in the past few years, a new, natural sound has joined the orchestra of automobiles and industry: gulls. To be more specific: Herring gulls.

Herring gulls—sea gull is the colloquial term for the entire gull family—are white or light gray, with rounded beaks that are made for fishing and scavenging. They’re usually found near the Arctic tundra, but recently Pittsburghers like Liz Buchanan have been noticing them hanging out near the Highland Park Bridge.

“Sometimes there seem to be hundreds as we cross," Buchanan said.

Ornithologist Bob Mulvihill from the National Aviary said the gulls’ presence is a really good sign for the area. It means the water in the Allegheny River and the surrounded environment is getting cleaner and more fertile.

“The rivers have more fish in them and the birds that rely on that source of food are finding their way here,” Mulvihill said. “They’re both reliant directly or indirectly on the quality of the water in the rivers, in the three rivers there.”

Land along the Allegheny River near Sharpsburg and Aspinwall, Pa., was once used for industrial purposes. Now, it's been cleaned up and much of it has been developed into a park, preserving the region's natural resources.
Credit Katie Blackley / 90.5 WESA

Efforts to improve the quality of Pittsburgh’s air and water over the years are paying off, Mulhivill said. Birds, like the Herring gulls, are able to find food in and around the city’s many rivers. The Allegheny has the highest local concentration of breeding Herring gull pairs, partially due to its water being cleaner than the other two rivers.

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“Birds, we have learned on a lot of levels, are really valuable bio-indicators of the quality of the environment,” Mulhivill said. “You know, what does the environment contain that’s beneficial to them or harmful to them?”

Sightings of Herring gulls in southwestern Pennsylvania were first recorded in the PA Breeding Bird Atlas in 1994. Since then, 40-50 breeding pairs have made their home in Pittsburgh.

Climate change also aided in the gulls’ decision to nest in the Steel City, with hotter temperatures impacting their usual northern habitats. The unseasonably warm weather is changing their patterns.

So far, as Buchanan pointed out, the gulls tend to stick near the Highland Park Bridge, rarely venturing toward downtown or the Point.

Mulvihill said it’s natural for birds new to an area to pick a spot and stay there for a bit. The first few pairs to visit Pittsburgh may have liked the site for its micro environment—maybe it catches the morning sun or shields them from harsh winds. The gulls do, after all, nest in the support structures like beams and warning bouys. It’s prime real estate for a Herring gull.

Herring Gulls rest along the base of the Highland Park Bridge on the Allegheny River, while others fly nearby on Thursday, May 18, 2017. The species is relatively new to the region, but increasing in population each year.
Credit Katie Blackley / 90.5 WESA

“It’s typical that when birds start building a population, the best sites from that species ecology point of view get occupied first,” Mulvihill said. “If and when their numbers increase, I think they’ll spread.”

Mulvihill said as long as Pittsburgh keeps on track cleaning up its environment, the city’s bird population will increase and diversify.

“We know that the environment is trending in the right direction,” Mulvihill said. “We don’t want to lose the ground we’ve gained.”

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