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JERALD J. DOSCH
ON DEAD BIRDS' TALES: MUSEUM SPECIMEN FEATHERS AS HISTORICAL ARCHIVES OF ENVIRONMENTAL POLLUTANTS
| THE STUFFY AND LITERALLY stuffed old birds found in museum collections around the globe have tales to tell. Locked in the leg tags and plumages of these preserved specimens are historical environmental records of when and where their feathers were grown, what the birds were eating at the time, and what levels of certain environmental toxins were present in the habitat in which they were living. By combining information from avian study skins with historical maps and industrial records it may now be possible to determine both the sources and sinks of certain environmental pollutants over time. |
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Humans have long used birds as indicators of local environmental health. The proverbial "canary in a coal mine" was a live, caged bird that miners carried with them deep underground. The unique, highly efficient and sensitive respiratory system of birds makes them very receptive to atmospheric conditions. Thus, if miners saw their caged bird die they knew hazardous carbon monoxide or methane gas levels had reached dangerous concentrations in the air and it was time to flee the mine.1 In 1962, Rachel Carson's Silent Spring used birds to highlight the environmental dangers of pesticides.2 That same decade other scientists used over seventeen-hundred eggs from museums and personal collections to demonstrate the link between the decline in several species of fish-eating birds, the thinning of their egg shells, and chlorinated hydrocarbon insecticides such as DDT and its metabolite DDE.3 More recently, scientists have begun using stable-carbon, nitrogen, and other isotope ratios in feathers and eggs to reconstruct the diets and movement patterns of birds.4 As biological archives, feathers also can be used to reconstruct environmental toxin levels decades or even centuries into the past. |
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Figure 1. Common Loons
Photo courtesy of the author.
These birds at the University of Minnesota's Bell Museum of Natural History have been collected and preserved since the late nineteenth century.
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Scientists began measuring the levels of heavy metals in bird feathers during the mid-1960s.5 Like the egg collections used to study the detrimental effects of DDT on avian reproduction, feathers from museum specimens also were used to track environmental pollutants through time. For example, a seminal 1966 paper using avian specimens from the Swedish Museum of Natural History documented fairly constant levels of mercury in Swedish birds collected from approximately 1840 to 1940; however, this was followed by a ten- to twentyfold increase during the 1940s and 1950s, likely due to the 1938–1940 introduction of alkyl-mercury compounds used to prevent fungal growth on seeds.6 As a result of this research, mercury-based seed dressings were banned in Sweden and later research once again used feathers to document the subsequent decline of mercury in birds.7 |
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Mercury, although naturally present in aquatic systems, has been and in some cases continues to be added to the environment through anthropogenic sources such as atmospheric deposition from the combustion of coal, point-source emissions from paper mills, and antimicrobial compounds. The primary anthropogenic sources of lead in aquatic habitats, also a naturally occurring element, are fishing tackle and hunting ammunition. Both of these heavy metals can cause illness, reproductive failure, and death, often on a grand scale. For example, lead poisoning killed more than one-hundred thousand Mallard ducks in Illinois in a single year, 1948, and continues to be a leading cause of mortality for loons in New England.8 |
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Feathers, a uniquely avian structure in extant species, are dermally derived, alive when growing, dead when completed, and strongly resistant to decay. Although birds can repair minor damage through daily preening, using their bills and/or feet to reconnect the microscopic, Velcro-like hooklets of a feather's vane, the only mechanism for excessive damage repair is replacement. While individual feathers can be accidentally lost and almost immediately regrown at any time, "molt," the process of shedding and replacing worn feathers en masse, usually takes place at regular age intervals and at specific times of the year.9 While all birds have at least one complete molt per year after the breeding season in which they replace all of their feathers in preparation for migration or winter survival, many birds also have a second molt before the spring mating season in which they may replace only some of their feathers. This second, prealternate molt largely serves to replace a bird's dull, more cryptic basic feather coat with a more colorful plumage better suited to attracting a mate and defending a territory. |
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Beta-keratin, the protein found in feathers, binds to and removes metals from the blood supply that nourishes a growing feather.10 As a result, the mature feather serves as an archive recording the metal levels that were circulating through a bird's body while it molted. The metals most likely entered the bird through its diet while the feather was growing, and thus knowing a bird's natural history provides clues not only to the time of year it molted, but what it typically ate and thus the proximate environmental source of the metals. Persistent environmental pollutants such as DDT, DDE, and heavy metals tend to build up or bioaccumulate within an organism over time and also become concentrated or biomagnified as they move up the food chain.11 As a result, longer-lived organisms near the top of the food chain, such as loons, sea birds, and eagles, which eat large fish for many years, tend to be particularly vulnerable to these pollutants. |
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The Common Loon (Gavia immer) is the official state bird of Minnesota, which hosts the largest breeding population of the species in the lower forty-eight United States.12 Metal toxicity is a significant cause of morbidity and mortality in loons.13 With the aid of Keith Kuwata, a colleague and analytical chemist from Macalester College, I have begun a research project to reconstruct historic heavy metal toxin levels using the feathers from loons collected in Minnesota for museum collections during the late nineteenth and early twentieth centuries. While several researchers and governmental agencies are interested in heavy metal loads found in loons alive today, we are unaware of any research that has "gone back in time" to reconstruct historical levels. Similarly, while anthropogenic sources of lead such as shotgun pellets and fishing tackle have been recognized as causes of avian toxicosis for over fifty years, I am unaware of any loon study that has examined the effects of naturally occurring (or presumably naturally occurring) background levels of lead and other metals or those from anthropogenic sources on a historical timescale.14 A common assumption is that the high heavy metal levels found in today's birds are due to human activities such as burning coal. We want to test that assumption. |
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I gathered preliminary data for this project by sampling feathers from Common Loon study skins in the collection of the Bell Museum of Natural History at the University of Minnesota and having them analyzed by the Diagnostic Center for Population and Animal Health at the University of Michigan. These birds were collected in Minnesota from 1898 to 1902 and included both males and females as well as juveniles and adults. The results are surprising in that arsenic, lead, mercury, and selenium were all present in all feathers sampled, with some levels being comparable to and occasionally even higher than the concentrations found in Minnesota loons from the 1990s.15 These initial results are surprising in that they suggest the presence of relatively high levels of all four metals in birds more than a century ago. However, the very small sample size of this preliminary data set is obviously of concern and demands a much more expansive study. Now a major challenge will be not only significantly increasing our sample size but also determining how much mercury and arsenic were added to the study skins during the preservation process and how much the birds actually acquired from their environment.16 |
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While it is obvious that typical museum collections are an invaluable resource for historical research, it is a relatively new methodology to use feathers from living birds or museum specimens as a tool for monitoring environmental pollution.17 Existing collections of museum specimens are invaluable, irreplaceable, and arguably underutilize resources for historical research. Their obvious value as windows to the past will only be amplified by requiring that collection activities continue so as to provide an unbroken record for future studies.18 Although most feather research is currently conducted by ecologists and environmental toxicologists, there is tremendous potential for collaborative, interdisciplinary work coupling historians, public policy researchers, ecologists and toxicologists. The stories are there, recorded in the feathers. They only need to be read. |
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Jerald J. Dosch is a visiting assistant professor at Macalester College in St. Paul, Minnesota. His ecological research interests include environmental toxicology, birds, tropical forest restoration, and the rigors of the winter season.
NOTES
The author wishes to thank Bob Zink and Mike Westberg for access to the collection of the Bell Museum of Natural History at the University of Minnesota.
1. Virginia H. Dale and Suzanne C. Beyeler, "Challenges in the Development and Use of Ecological Indicators," Ecological Indicators 1 (2001): 3–10; Noble S. Proctor and Patrick J. Lynch, Manual of Ornithology: Avian Structure and Function (New Haven: Yale University Press, 1993), 2.
2. Rachel Carson, Silent Spring (Boston: Houghton Mifflin, 1962).
3. Joseph J. Hickey and Daniel W. Anderson, "Chlorinated Hydrocarbons and Eggshell Changes in Raptorial and Fish-Eating Birds," Science 162 (1968): 271–273.
4. Keith A. Hobson, "Stable-carbon and Nitrogen Isotope Rations of Songbird Feathers Grown in Two Terrestrial Biomes: Implications for Evaluating Trophic Relationships and Breeding Origins," The Condor 101 (1999): 799–805; Jeffrey F. Kelly and Deborah M. Finch, "Tracking Migrant Songbirds with Stable Isotopes," Trends in Ecology and Evolution 13 (1998): 48–49; Peter Mara, Keith A. Hobson, and Richard T. Holmes, "Linking Winter and Summer Events in a Migratory Bird by Using Stable Carbon Isotopes," Science 282 (1998): 1884–86; and numerous others.
5. Joanna Burger, "Metals in Avian Feathers: Bioindicators of Environmental Pollution," Reviews in Environmental Toxicology 5 (1993): 203–311.
6. W. Berg et al., "Mercury Content in Feathers of Swedish Birds from the Past 100 Years," Oikos 17 (1966): 71–83.
7. T. Westermark, T. Odsjö, and A. G. Hohnels, "Mercury Content in Bird Feathers Before and After Swedish Ban on Alkyl Mercury in Agriculture," Ambio 4 (1975): 87–92.
8. Glen C. Sanderson and Frank C. Bellrose, A Review of the Problem of Lead Poisoning in Waterfowl, special publication number 4 (Champaign, Illinois: Natural History Survey, 1986); Inga F. Sidor et al., "Mortality of the Common Loon in New England, 1987–2000," Journal of Wildlife Diseases 39 (2003): 306–15.
9. Frank B. Gill, Ornithology, 3rd ed. (New York: W. H. Freeman and Company, 2007), 89.
10. Burger, "Metals in Avian Feathers," 214.
11. G. W. Bryan, "Bioaccumulation of Marine Pollutants," Philosophical Transactions of the Royal Society of London B. 286 (1979): 483–505.
12. Paul I. V. Strong and Richard J. Baker, An Estimate of Minnesota's Summer Population of Adult Common Loons (St. Paul: Minnesota Department of Natural Resources, 1991).
13. Joanna Burger et al., "Heavy Metal Concentrations in Feathers of Common Loons (Gavia immer) in the Northeastern United States and Age Differences in Mercury Levels," Environmental Monitoring and Assessment 30 (1994):1–7; Karen L. Ensor, Dan D. Helwig, and Lauren C. Wemmer, Mercury and Lead in Minnesota Common Loons (Gavia immer) (St. Paul: Water Quality Division, Minnesota Pollution Control Agency, 1992); Mark Pokras and Rebecca Chafel, "Lead Toxicosis from Ingested Fishing Sinkers in Adult Common Loons (Gavia immer) in New England," Journal of Zoo and Wildlife Medicine 23 (1992): 92–97; Inga F. Sidor et al., "Mortality of the Common Loon in New England, 1987–2000," Journal of Wildlife Diseases 39 (2003): 306–15; and others.
14. Vernon G. Thomas and Mark A. Pokras, "International Analysis of Non-toxic Shot Adoption for Waterfowling," in International Union of Game Biologists 21st Congress, ed. Ian D. Thompson (Chalk River, Ontario: Canadian Forestry Service, 1993): 35–40.; Cynthia Perry, Lead Sinker Ingestion in Avian Species, Division of Environmental Contaminants Information Bulletin 94–09–01 (Arlington, Virginia: U.S. Fish and Wildlife Service, 1994).
15. Jimmy Pichner and Peregrine L. Wolff, "Causes of Morbidity and Mortality in the Common Loon, Gavia immer, in Minnesota, 1991–1996," (Apple Valley, Minnesota: Zoological Gardens, 1996); also additional unpublished data from Jimmy Pichner (copy in possession of author).
16. Barbara Smith and Bill Coulehan, "Potential Exposure to Arsenic and Other Highly Toxic Chemicals When Handling Museum Artifacts," Applied Occupational and Environmental Hygiene 17 (2002): 741–43; Berg, Sjöstrand, and Westermark, "Mercury Content."
17. Deborah A. Rocque and Kevin Winkler, "Use of Bird Collections in Contaminant and Stable-isotope Studies," The Auk 122 (2005): 990–94.
18. Thomas B. Smith, et al., "A Call for Feather Sampling," The Auk 120 (2003): 218–21.
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