A Canadian wildlife organization is raising questions about the future of an iconic Canadian bird, linking pollution to the declining reproductive success of the common loon.
In a document published last month, Bird Studies Canada reports that while the population of loons on Canadian lakes remained stable between 1992-2010, the number of young raised to six weeks of age declined. At six weeks, loons are larger and more likely to be raised to independence.
“We found a number of interesting patterns, but one of them was that across the country as a whole, reproductive success is going down over time, but it’s still high enough to maintain numbers of breeders out there on the lakes,” said Doug Tozer, a scientist with the organization and author of the report. “So this is sort of like the first warning of something worse to come later, perhaps.”
The report uses data collected from the organization’s regular survey work conducted by scientists and volunteers.
The numbers reveal that a pair of loons produce 0.6 young per year, said Tozer, an average created using national numbers. Numbers from the early 1990s were closer to one. The report says an average annual reproductive success of at least 0.48 is enough to sustain the number of breeders.
As loons can live over 20 years, the declining breeding success will take time to show itself in the population numbers, said Tozer.
“You can’t be totally sure the decline will continue in the same manner that we see in this 30-year, 20-year data set, but if you assume that it is going to continue that way, which it could, we might get down to a point where reproductive success is low enough to start causing a reduction in the number of breeders we see on lakes in a few decades,” said Tozer.
The organization is linking the decline to higher mercury levels in lakes and acid precipitation from fossil fuels. Lakes with higher acidity are home to fewer fish and higher mercury levels have been shown to affect loons’ behaviour.
“They’re not as good at incubating eggs and feeding young and that’s why it reduces their reproductive success.”
Runoff from nutrients linked to agricultural and animal production, while still problematic, might actually reduce mercury levels.
A 2011 report from the Biodiversity Research Institute studying mercury in the Great Lakes region found their presence had a diluting effect, decreasing mercury levels in fish.
“The increased algal biomass at the base of the food web tends to biodilute the methylmercury, even in individual basins within large lakes … resulting in lower concentrations in fish and other animals at the top of the food web as compared to levels in more mercury-sensitive watersheds,” said the report.
Concerning other species of birds, populations across Canada have dropped by 12 percent since 1970, acc-ording to Bird Studies Canada data.
Internationally, one in eight bird species is threatened with extinction, according to BirdLife International, which attributes agricultural intensification, infrastructure development, pollution and climate change to declines.