John Beetham of DC Birding Blog, whose curation of noteworthy bird notes every week is among the very best of any subject on the web, draws attention to a recent study that offers a great deal of insight into one of the more insidious and quiet killers of wild birds in North America, mercury poisoning.
We’re well aware of mercury’s effects as a neurotoxin on human populations such that stringent restrictions are placed on its disposal, but methylmercury has been documented in several bird species as well and while we don’t know the extent of how it manifests in birds, we do know that it can impact learning and memory (much as it does in humans). This means that birds affected by mercury in their environment can have difficulty memorizing and retaining songs, among other things.
That study Beetham elaborates on was one authored by Sheila Scoville and Oksana Lane and published in the Bulletin of Environmental Contamination and Toxicology concerning the analysis of the tissues of a young Saltmarsh Sparrow, particularly the bird’s brain, which suggested disturbing things about the omnipresence of mercury in many ecosystems.
Based on feather samples taken from adult birds at the study site, it can be inferred that this fledgling’s mother had high exposure to mercury at the time that she laid her eggs. This is analogous to in utero exposure in humans. In humans, in utero exposure can lead to brain abnormalities like Minamata Disease. This fledgling Saltmarsh Sparrow showed abnormalities in its cerebellum
that would have similar effects on motor control and coordination. Birds with these sorts of defects would have trouble recognizing and escaping danger, thus making them more susceptible to predation and accidental deaths.
While this fledgling Saltmarsh Sparrow is only one data point, the findings have disturbing implications. Since mercury levels among adult birds were so high, many other young Saltmarsh Sparrows are presumably exposed to mercury at the time of egg formation. We cannot know how many of them have brain abnormalities like the one documented in this study, but it seems safe to assume that the problem is widespread.
It’s hard to know precisely what to do about this issue. Chief among contributing factors are coal-burning power plants, which are the single greatest source of methylmercury in the environment. In addition to climate concerns, it seems critical that we shift away from coal as an energy source to reduce the amount of mercury entering these ecosystems for the sake of those birds, and other wildlife, that are clearly feeling the stress.
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