Published Date Written by David EastmanAnyone fortunate to view some of the videos at the Loon Center in Moultonborough has to remark how unfortunate it is for the incubating female loons to put up with incessant black flies also co-habiting the northern woodland lakes they breed in. The small biting flies cover the smooth black head of the stoic loon parent, and cause quite an uncomfortable reaction from us as we view this seasonal torture. We unconsciously hope these buzzing bugs don't bother this wilderness loving northern diver as much as it surely would us. Now a young grad student has found loons really are affected by these tormentors, and it can significantly matter in their reproductive success over their four weeks on the nest.
The 2011 LPC summer newsletter featured an article by biologist John Cooley as he revealed Meggin Weinandt's work — where she found out it is the loon's feathers themselves acting as an attractant for the vicious biting black flies. The Northern Michigan graduate student even found that a specialist species of black fly, Similium annualus (Lundrs.), was an added insult to the loon's misery. John had to remark about the subtlety of a species that has apparently evolved a preference for its loon host, as the black fly hatches out of a coldwater stream, and then heads for a nearby lake searching for a loon. Locating that big bird over hundreds of acres of surface waters has to be a task.
Weinandt's experimental work confirmed that captured black flies target loons, and that a chemical cue — presumably from the loon's natural waterproofing oil on the wing feathers — was the likely attractant.
Furthermore, during two of her three trials, the only species of black fly captured was the aforementioned species.
To stimulate a nesting bird, Weinandt equipped loon, goose, and duck decoys with flypaper traps and exposed them for brief periods on lake shorelines. She hoped to determine the black fly species present, and their host preferences. And to research whether the flies used scent cues or sight to find the birds, some decoys were actually outfitted with real wings salvaged from recent loon mortalities. What she found was striking: the loon decoy with real wings attracted over 90 percent of all the black flies trapped on any decoy! In fact, when the loon wings were attached to the goose decoy, the flies followed suit, swarming that fake goose, too.
Weinandt also investigated the microorganisms that the black flies can deposit in their loon host as they feed. Dozens of the flies crawl around the loon's eyes and bill, burrowing into the soft iridescent feathers of the head with specialized claws. In other bird species these blood parasites, akin to human malaria, are known to lower the reproductive success of the host bird, compromise its immune system, or perhaps killing it outright.
Through genetic analysis of loon blood samples from Wisconsin, Weinandt detected several common avian blood parasites, previously unreported in the common loon. Her results were consistent with preliminary findings from the New Hampshire work of Tufts veterinary student Heather Crispell in 2010, where blood parasites were also detected.
Then, here is a kicker. Weinandt compared parasite infections with blood mercury levels. More mercury, it turned out, was associated with a higher likelihood of blood parasite infection. So, the result suggests that mercury, in addition to poisoning a loon's nervous system, may compromise the loon immune response. Which, in this case, is the ability to fight off blood parasites introduced by black flies. A cause and effect between mercury and parasites was beyond the scope of her graduate study, and testing for that would take more research work, she admitted.
This is a complex natural history, helping to explain black fly impacts beyond the immediate nesting torment we flinch from while seeing. We may not be able to limit the numbers of black flies throughout the northern forest and its lakes, but we could do something about adding mercury to the environment. This is becoming a dangerous factor to birdlife in the Northeast, and is deplorable as a pollutant.
Meggan L. Weinandt's Master's 86 page thesis written in 2006 was entitled: Conservation implications of Common Loon (Gavia immer) parasites: black flies, haematozoans, and the role of mercury. Northern Michigan University is located in Marquette, Mich. For us humans, we will probably choose to remain behind screened enclosures while the loon population has to put up with swarming black flies in the worst of the season they reproduce in. Joining the Loon Preservation Committee as a member can help.
There are times, however, when the black fly infestation becomes so severe that it does drive the loons off their nests that summer, leading to reproductive failure as the eggs become abandoned. This primitive waterfowl has a lot to put up with to continue existing.