Editing Common loon (section)

==== Effects of mercury and acid rain pollution on health and brood productivity ====
The common loon is a key indicator of [[Mercury (element)|mercury]] deposition in aquatic environments due to its position at the top of the [[food chain]].<ref name=":10">{{Cite journal |last1=Evers |first1=David C. |last2=Savoy |first2=Lucas J. |last3=DeSorbo |first3=Christopher R. |last4=Yates |first4=David E. |last5=Hanson |first5=William |last6=Taylor |first6=Kate M. |last7=Siegel |first7=Lori S. |last8=Cooley |first8=John H. |last9=Bank |first9=Michael S. |last10=Major |first10=Andrew |last11=Munney |first11=Kenneth |date=2008-02-01 |title=Adverse effects from environmental mercury loads on breeding common loons |url=https://doi.org/10.1007/s10646-007-0168-7 |journal=Ecotoxicology |language=en |volume=17 |issue=2 |pages=69–81 |doi=10.1007/s10646-007-0168-7 |pmid=17909967 |bibcode=2008Ecotx..17...69E |s2cid=17769869 |issn=1573-3017|url-access=subscription }}</ref> The main contributors to elevated mercury concentrations in aquatic environments are coal burning power plants, waste incineration, and metal production.<ref name=":19">{{Cite web |title=Threats to Loons |url=https://www.adkloon.org/threats-to-loons |access-date=2022-03-07 |website=Adirondack Center for Loon Conservation |language=en-US}}</ref> Although environmental mercury (Hg) is naturally occurring, [[methylmercury]] ({{chem2|CH3Hg+}}, sometimes written as {{chem2|MeHg+}}) is a biologically toxic form that accumulates throughout aquatic environments in the northeastern United States.<ref name=":20">{{Cite journal |last1=Schoch |first1=Nina |last2=Glennon |first2=Michale J. |last3=Evers |first3=David C. |last4=Duron |first4=Melissa |last5=Jackson |first5=Allyson K. |last6=Driscoll |first6=Charles T. |last7=Ozard |first7=John W. |last8=Sauer |first8=Amy K. |date=April 2014 |title=The Impact of Mercury Exposure on the Common Loon (Gavia immer) Population in the Adirondack Park, New York, USA |url=https://bioone.org/journals/waterbirds/volume-37/issue-sp1/063.037.sp116/The-Impact-of-Mercury-Exposure-on-the-Common-Loon-Gavia/10.1675/063.037.sp116.full |journal=Waterbirds |volume=37 |issue=sp1 |pages=133–146 |doi=10.1675/063.037.sp116 |s2cid=85674745 |issn=1524-4695|url-access=subscription }}</ref> Methylmercury, a [[neurotoxin]], has been shown to have a wide range of behavioral, reproductive, and survival effects on the common loon.<ref name=":21">{{Cite journal |last=Schoch |first=Nina |date=2006-01-01 |title=The Adirondack Cooperative Loon Program: Loon Conservation in the Adirondack Park |url=https://digitalworks.union.edu/ajes/vol13/iss2/5 |journal=Adirondack Journal of Environmental Studies |volume=13 |issue=2 |issn=1075-0436}}</ref> Previous research has found a correlation between mercury levels and [[pH]], with more acidic aquatic environments being at the highest risk for elevated methylmercury concentrations.<ref name=":22">{{Cite journal |last1=Yu |first1=Xue |last2=Driscoll |first2=Charles T. |last3=Montesdeoca |first3=Mario |last4=Evers |first4=David |last5=Duron |first5=Melissa |last6=Williams |first6=Kate |last7=Schoch |first7=Nina |last8=Kamman |first8=Neil C. |date=2011-10-01 |title=Spatial patterns of mercury in biota of Adirondack, New York lakes |url=https://doi.org/10.1007/s10646-011-0717-y |journal=Ecotoxicology |language=en |volume=20 |issue=7 |pages=1543–1554 |doi=10.1007/s10646-011-0717-y |issn=1573-3017 |pmc=3175042 |pmid=21691858|bibcode=2011Ecotx..20.1543Y }}</ref> Once mercury enters the water, it is taken up by fish and spread throughout the food chain.<ref name=":19" /> Resulting from this transmission of mercury, there is a significant positive correlation between mercury levels in fish and mercury levels in male, female, and chick blood of common loons; consequently, an increase in mercury concentration in the blood of common loons and fish was seen with a decrease in local aquatic pH.<ref name=":16">{{Cite journal |last1=Champoux |first1=L. |last2=Masse |first2=D. C. |last3=Evers |first3=D. |last4=Lane |first4=O. P. |last5=Plante |first5=M. |last6=Timmermans |first6=S. T. A. |date=September 2006 |title=Assessment of mercury exposure and potential effects on common loons (Gavia immer) in Québec |url=http://link.springer.com/10.1007/s10750-006-0066-7 |journal=Hydrobiologia |language=en |volume=567 |issue=1 |pages=263–274 |doi=10.1007/s10750-006-0066-7 |issn=0018-8158 |s2cid=10621451|url-access=subscription }}</ref> Although there have been reductions in recent years in acidifying emissions, there has been limited biological recovery in these lakes most likely due to climate change.<ref name=":6">{{Cite journal |last1=Bianchini |first1=Kristin |last2=Tozer |first2=Douglas C. |last3=Alvo |first3=Robert |last4=Bhavsar |first4=Satyendra P. |last5=Mallory |first5=Mark L. |date=October 2020 |title=Drivers of declines in common loon (Gavia immer) productivity in Ontario, Canada |url=https://linkinghub.elsevier.com/retrieve/pii/S0048969720332447 |journal=Science of the Total Environment |language=en |volume=738 |pages=139724 |bibcode=2020ScTEn.73839724B |doi=10.1016/j.scitotenv.2020.139724 |pmid=32531589|s2cid=219620784 |url-access=subscription }}</ref> Research has shown that warmer summer temperatures can inhibit reestablishment of cold-water fish species in acidified lakes and droughts brought on by increased summer temperatures can further acidify lakes.<ref name=":6" />

Although the common loon is able to decrease their methylmercury levels by molting and laying eggs, continued consumption of fish with raised methylmercury levels prevents these mechanisms from effectively lowering methylmercury levels.<ref name=":21"/> Mercury concentrations have been shown to vary by the sex and age of common loons. Male common loons were found to contain the highest blood mercury concentration likely due to the fact that they tend to consume bigger fish with higher mercury concentrations.<ref name=":17">{{Cite journal|last1=Schoch|first1=Nina|last2=Glennon|first2=Michale J.|last3=Evers|first3=David C.|last4=Duron|first4=Melissa|last5=Jackson|first5=Allyson K.|last6=Driscoll|first6=Charles T.|last7=Ozard|first7=John W.|last8=Sauer|first8=Amy K.|date=April 2014|title=The Impact of Mercury Exposure on the Common Loon ( Gavia immer ) Population in the Adirondack Park, New York, USA|url=http://www.bioone.org/doi/abs/10.1675/063.037.sp116|journal=Waterbirds|language=en|volume=37|issue=sp1|pages=133–146|doi=10.1675/063.037.sp116|s2cid=85674745|issn=1524-4695|url-access=subscription}}</ref> Females contained the second highest blood mercury concentration with differences between the males likely being due to the fact that females can expel mercury into the eggs they lay.<ref name=":16" /> Juveniles had the lowest blood mercury concentration.<ref name=":18">{{Cite journal|last1=Burgess|first1=Neil M.|last2=Meyer|first2=Michael W.|date=February 2008|title=Methylmercury exposure associated with reduced productivity in common loons|url=http://link.springer.com/10.1007/s10646-007-0167-8|journal=Ecotoxicology|language=en|volume=17|issue=2|pages=83–91|doi=10.1007/s10646-007-0167-8|pmid=18038272|bibcode=2008Ecotx..17...83B |s2cid=40571426|issn=0963-9292|url-access=subscription}}</ref> Scientists found that the data from juveniles helped to best indicate the local mercury availability as they are fed exclusively from their natal territory.<ref name=":16" />

Elevated levels of mercury have been associated with changes in foraging and [[brooding]] behavior among adult common loons, especially in higher concentrations.<ref name=":18" /> Studies have found that elevated levels of methylmercury are associated with lethargy and decreased time spent foraging in adult common loons.<ref name=":10" /> A different study carried out in the [[Adirondack Mountains]] found that elevated levels of methylmercury are associated with reduced diving frequency in adult common loons.<ref>{{Cite journal |last=Stewart |first=Paul A. |date=January 1967 |title=Diving Schedules of a Common Loon and a Group of Oldsquaws |journal=The Auk |volume=84 |issue=1 |pages=122–123 |doi=10.2307/4083265 |jstor=4083265 |issn=0004-8038|doi-access=free }}</ref> One study found that brood productivity was reduced by half when female blood mercury levels exceeded 4.3 μg/g and productivity completely failed when female blood mercury levels exceeded 8.6 μg/g. These results are related to fish mercury levels of 0.21 μg/g and 0.41 μg/g, respectively.<ref name=":18" /> As mercury levels and pH are correlated, scientists have found that brood success decreases with decreasing pH such that environments with a pH at around 4.5 exhibited reproductive success below a calculated positive growth rate threshold.<ref name=":6" /> An association has also been observed between elevated blood methylmercury levels and aberrant incubation patterns.<ref name=":10" /> Adult common loons with high levels of methylmercury were found to spend less time incubating and in the nest, increasing the risks of [[predation]] and the eggs overheating/overcooling.<ref name=":10" /> Together, the effects of heightened methylmercury levels on parenting behaviors may contribute to lower chick survival rates. One study in Maine and New Hampshire found that high levels of methylmercury in parents are associated with a significant decrease in the number of fledged young, with common loons in the highest risk group producing 41% fewer fledged young than common loons with low levels of methylmercury.<ref name=":10" />