A new study by researchers at the University of British Columbia has found that the seagull population in the Strait of Georgia has fallen by 50 per cent since the 1980s.
The finding was based on data collected over a century on population numbers on the Glaucous-winged Gulls, which are the most common species of the seagull in the Lower Mainland, Victoria and elsewhere on the South Coast of B.C.
The population of the species of seabird grew rapidly in the early 1900s but it declined rapidly beginning in the mid-1980s when their marine food availability changed.
It is estimated that the population declined to about 5,600 nesting pairs in 2010, which is approximately 7,400 fewer pairs than the 13,002 pairs in 1986. However, the 2010 figure is similar to the 5,654 to 6,654 pairs estimated in the region during the middle of the population increase phase in 1960.
“These birds are the ultimate generalist — they can eat whatever’s around,” says the study’s lead author Louise 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.”
“Gulls are an indicator of our coastal marine ecosystems,” adds Blight. “We need to be restoring ecosystems along the coast, and that includes restoring fish populations.”
The local population of seagulls has historically relied on a marine diet of eating small fish and shellfish, but over time with the growth of the human population they have transitioned into a diet that also consists of foods found on land including garbage and earthworms.
Researchers believe the seagulls’ successful egg production process requires a diet largely comprised of high-protein fish rather than lower-quality anthropogenic garbage. Seagull eggs have generally become smaller and fewer in number in recent decades.
Furthermore, there have been instances of cannibalism in some colonies experiencing food shortages. Predation by eagles is also a contributing factor with the recent resurgence in the local eagle population.
Seagulls have an average lifespan of between 10 to 15 years. Their eggs take about one month to hatch.