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Seagull population down by half on South Coast of B.C.: UBC study

Feb 28. 15

By Tiffany Crawford, Vancouver Sun

The population of seagulls in the Strait of Georgia has declined by half in the past three decades, in part because a lack of marine food, according new research from the University of B.C.

Researchers analyzed 111 years of data collected during bird counts on glaucous-winged gulls, the most common seagull species on B.C.'s southern coat. They found the population increased rapidly beginning in the early 1900s, but started to drop after the mid-1980s and has been on a steady decline since.

Using bird counts from breeding colonies in the Georgia Basin, researchers say there were 5,600 nesting pairs in 2010, the latest number available, down by 57 per cent from 13,002 pairs in 1986.

Louise Blight, the study's lead author, said research indicates that diet is one of the main factors in the decline of the bird's health.

"These birds are the ultimate generalist — they can eat whatever's around," said Blight. "If they are experiencing a population decline, the gulls may be telling us that there have been some fairly profound changes to local marine ecosystems."

She said gulls historically relied on a marine diet, largely eating shellfish and small fish like herring. Over time they incorporated more food found on land, such as garbage and earthworms.

"It's not that they are preferentially going after this food. But they are eating things like french fries or bits of fried chicken or that sandwich they just snatched out of your hand. They are generalists, so they can survive on this food but they do need a high-protein fish."

The theory is that high-protein fish, as opposed to lower quality garbage, may be critical for successful egg production. Blight said there is evidence that seagull eggs have become fewer in number and smaller in size over the past few decades.

The research also suggests that food shortages may lead to cannibalism in some bird colonies.

"They're presumably turning to land-based prey sources because the things they prefer to eat are less available," said Blight, although she noted that the study did not look at fish populations.

"I can't speak to that in detail but there is evidence out there, for example herring spawning is decreasing in the Georgia Strait. We also know that they used to feed on oolichan, but that is an endangered species and is not available for gulls."

Study co-author Peter Arcese, with UBC's faculty of forestry, said reductions in marine food abundance and quality help explain why the population of two other bird species in the region — the marbled murrelets and western grebes — have declined by 90 per cent.

The study was published earlier this month in the online journal The Condor: Ornithological Applications.

Seagull facts


The glaucous-winged gull, most abundant in coastal cities and towns of the Pacific Northwest, has a white head and under parts, and grey wingtips. They have pink legs and a yellow beak with a red spot. Their forehead is somewhat flat.


They make a whistling "keow" noise.


Glaucous-winged gulls live on average about 15 years, but some have been found to live into their early 20s, though that is rare. They nest in the summer, and each pair on average produces two or three chicks which fledge at six weeks.


They are scavengers of dead or weak animals, including small fish, and shellfish like mussels and clams. They also scavenge for garbage and will eat just about any kind of human food, but have also been known to munch on small rodents and pigeons, as well as glaucous-winged gull chicks. They use a variety of feeding methods, including plunge-diving, diving from the surface and dropping shellfish on rocks.

Why should we care if they decline?

While some might not like seagulls because they steal food or poop on your car, they are an integral part of the coastal ecosystem. If seagulls are declining because of a shortage of marine food, it could mean other coastal creatures are under threat of declining or becoming endangered.

Source: The Cornell Lab of Ornithology, Louise Blight, UBC

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