California brown pelicans usually nest and hatch chicks in Southern California and Mexico. But in the past two years, scientists have seen them building nests much farther north on an island in the Columbia River.
The unusual nesting behavior follows a northward shift in the birds’ migratory patterns over the past three decades, according to Oregon State University seabird ecologist Dan Roby. He noted that a similar pelican species has also been moving north and expanding its breeding range on the East Coast, which suggests it could be linked to climate change.
“I think we can expect it to continue, and it’s probably linked to global climate change because quite a few birds are shifting their range farther and farther north as the climate warms,” he said.
Since the 1980s, scientists have documented brown pelicans regularly flying as far north as British Columbia to feed along the coasts of Oregon and Washington during the summer. When it comes to nesting and breeding in the spring, however, they haven't ventured very far north of the Channel Islands in Southern California.
But last spring, while monitoring colonies of double-crested cormorants and Caspian terns on East Sand Island at the mouth of the Columbia River, Roby noticed three pairs of California brown pelicans had built nests and laid eggs on the island.
“That’s a big leap from the Channel Islands of California to come all the way up to the border of Oregon and Washington and start to breed there,” he said.
None of the eggs hatched, but this year he’s noticed two more nests that were built by birds in breeding condition — with bright red gular pouches under their bills.
“At least two pairs in that condition have built nests and have been seen copulating,” Roby said. “We’re hopeful that this year they may produce fertile eggs and hatch young.”
Deborah Jaques, an independent wildlife biologist based in Astoria, Oregon said pelicans haven't just been coming up north earlier — they've also been staying in the Northwest later in the year. A couple times in recent years, the pelicans that waited too long to head back south have died in early winter storms. Still, she was surprised to learn that they have started building nests in the Columbia River estuary.
"To me, it was earth-shaking," she said. "It’s never been recorded in modern history to have pelicans nesting this far north. The farthest north they've been known to nest before now was in Monterey in the '50s. Other than that, it’s always been confined to Southern California."
Breeding rates have declined in pelican colonies in Southern California and Mexico over the past three years as sardine populations in those areas have declined, Jaques said. So, it's possible pelicans are lacking the food they need farther south and are finding it farther north.
"So something may have shifted in the desirability of this area, or it could have to do with the fact that there has been fishery declines in the southern part of their range in Southern California," she said. "I think there could be a climate change connection. It’s just very complicated. It would be based on how climate change is affecting fisheries and ocean currents."
Shawn Stephensen, a wildlife biologist with the Oregon Coast Wildlife Refuge Complex in Newport, has been doing aerial surveys since 2008 of pelicans along the Oregon and Washington coasts every September. He says he’s been noticing a northward shift in pelicans within the survey area of the Oregon and Washington coastline.
“The first few years we did the survey there were hundreds of birds scattered out along the Oregon coast, but in recent years there haven’t been as many birds farther south,” he said.
Roby said he thinks it may be just a matter of time before he sees a colony of breeding pelicans on East Sand Island.
“And that would be pretty neat because this is a bird that before 2009 was listed as endangered,” he said.
The brown pelican population was heavily impacted by the use of the pesticide DDT, which prevented the birds' eggs from hatching. DDT was banned in 1972, and the birds have made a comeback since then. The pelicans' breeding range expansion could be beneficial to the recovery of the species as a whole, Roby said. But if it is connected to climate change, the benefits might be offset by other impacts.
"It depends on what happens on the southern end of their range, where things may not be as positive for California brown pelicans," he said.