High levels of contaminants are linked with thinner eggshells in the ivory gull, a red-listed high Arctic seabird.
The ivory gull, a rare high Arctic seabird that is one of the most northerly nesting birds on the planet, has enough contaminants in its body to cause its eggshells to thin, Norwegian and Russian researchers have found.
The eggshell thinning is significant enough that the researchers suggest it may contribute to the gull’s population declining of up to 80 per cent in some areas. There are only an estimated 8000–11500 breeding pairs of ivory gulls worldwide.
“This is very concerning,” says Cecilie Miljeteig, a biologist from the Norwegian University of Science and Technology and lead author of the study, published earlier this year in the scientific journal Science of the Total Environment. “Pollution is not the only threat to this species – it is ice-dependent, which means that global warming is also a threat.”
Organochlorinated pesticides and other contaminants have long been known to cause eggshell thinning in birds, but the researchers’ findings are the first to document eggshell thinning in the ivory gull. Previous studies conducted by the same researchers have documented that ivory gull eggs have the highest known concentrations of PCBs and DDT of any Arctic seabird.
Miljeteig and her colleagues from the Norwegian Polar Institute, the Russian Arctic and Antarctic Research Institute and the Norwegian School of Veterinary Science sampled 35 ivory gull eggs from four colonies on Svalbard and northwestern Russia and tested the eggs for a range of contaminants, including organochlorinated pesticides (DDT and DDE), PCBs, brominated flame retardants and mercury.
They also measured the shell thickness of the eggs they sampled and found that thinner eggshells were associated with higher contaminant levels in the eggs. The eggshells were also as much as 17 % thinner than those of archived ivory gull eggs from before 1930.
The ivory gull feeds near the top of the food chain, which causes it to accumulate high levels of contaminants that have been biomagnified in its food. Industrial pollutants, such as pesticides and PCBs, are transported to the Arctic by winds and weather, and persist there because their chemical structure makes them resistant to breakdown. Thus many long-banned pollutants continue to pose problems for Arctic animals and birds.
Eggshell thinning associated with the pesticide DDT and its breakdown products led to severe population declines in some birds of prey after 1945, including the bald eagle, the California condor and the peregrine falcon. A growing awareness of the environmental effects of DDT led to its subsequent ban for use beginning in the 1970s. It was banned worldwide for most uses by the Stockholm Convention in 2001.