Seagull numbers fall by half in 30 years
Diet is main factor for decline, researchers say
The population of seagulls in the Strait of Georgia has dropped by half over the last three decades, in part because a lack of food from the ocean, according to new research from the University of B.C.
Researchers collected 100 years of data on Glaucous-winged Gulls, the most common species on B.C.’s South Coast and found the population increased rapidly from the early 1900s, but started to drop after the mid-1980s.
Using bird counts from breeding colonies in the Georgia Basin, researchers say in 2010 there were 5,600 nesting pairs, down by 57 per cent from 13,002 pairs in 1986. They also discovered diet is one of the main factors in the decline of the bird’s health, according to a UBC news release Friday.
“These birds are the ultimate generalist — they can eat whatever’s around,” said Louise Blight, the study’s lead author. “If they are experiencing a population decline, the gulls may be telling us there have been some fairly profound changes to local marine ecosystems.”
Blight said gulls historically relied on almost a purely marine diet, largely eating small fish and shellfish, but over time moved to a diet that incorporated more foods found on land.
The theory is that access to high-protein fish, as opposed to lower-quality anthropogenic garbage, may be critical for successful egg production in some species. The research suggests food shortages may also lead to cannibalism in some colonies.
“They’re presumably turning to land-based prey sources because the things they prefer to eat are less available,” Blight said, adding there needs to be more focus on restoring ecosystems along the coast, including fish populations.