Ivory Gull (Pagophila eburnea) is one of those species, birders will travel across the country to try to see if one shows up somewhere in the lower 48 states. Birders from around the country flocked to see one in Quincy, Illinois this January. The bird’s presence even made it to the front page of the Chicago Tribune. Those that saw it will be talking about it for years, as will those that didn’t (like me). The reason is that this beautiful all white bird normally lives at the highest latitudes in the Arctic even in the winter. The photo here is one Josh Engel took of the Quincy bird.
However, this blog post is not really about that bird. It is about what a newly published study on Ivory Gulls and what may be behind a precipitous decline in their populations. This study, by Alex Bond, Keith Hobson, and Brian Branfireun just appeared in the Proceeding of the Royal Society of London, series b, and it used museum specimens in a way that the original collectors of these specimens could never have imagined. The Bond et al. study was carefully designed to assess the temporal patterns they were investigating, the study highlights that the activities of humans are influencing the entire planet in ways that go far beyond climate change. Mercury is a rare element in the natural environment. However, it can accumulate and it has been accumulating fast in marine systems especially at high latitudes. It gets concentrated in animals that are at the top of the food chain. Ivory Gulls may not seem like something that would be at the top, but they are. They frequently scavenge on carcasses of marine mammals, so Ivory Gulls are eating top carnivores. The authors sampled feathers from 80 museum specimens going back to the 1870s. Only 2 of our 44 Field Museum specimens of this species met the geographic criteria they were looking for; these two birds were collected in 1896 in Newfoundland. Their analysis shows that Ivory Gulls today have significantly increased amounts of mercury than they did in in the past. The authors also gathered data on nitrogen isotopes and found that the ratios of these isotopes did not vary for the same samples. Nitrogen correlates with aspects of diet and the lack of change across 130 years indicates that the mercury accumulation in modern Ivory Gulls is not due to changes in the diets of these birds through time, which bolsters their conclusion that this accumulation appears to be due to the general increase in the environment as a whole.
In their discussion, Bond et al. cite other studies of other birds including Rusty Blackbird (Euphagus carolinus), Wandering Albatross (Diomedia exulans) and Clapper Rails (Rallus longirostris) where high mercury levels are thought to reduce breeding activity and success. The Bond et al. paper is just another example of the incredible ways in which the time series of specimens in museum collections can be used. Ridding the high arctic environments of an excess of mercury will not be easy, but we have to recognize these problems if we are going to find solutions.