Marilyn G. Spalding

Nineteenth Century Mercury: Hazard to Wading Birds and Cormorants of the Carson River, Nevada

Contemporary mercury interest relates to atmospheric deposition, contaminated fish stocks and exposed fish-eating wildlife. The focus is on methylmercury (MeHg) even though most contamination is of inorganic (IoHg) origin. However, IoHg is readily methylated in aquatic systems to become more hazardous to vertebrates. In response to a classic episode of historical (1859–1890) IoHg contamination, we studied fish-eating birds nesting along the lower Carson River, Nevada. Adult double-crested cormorants (Phalacrocorax auritus), snowy egrets (Egretta thula) and black-crowned night-herons (Nycticorax nycticorax) contained very high concentrations of total mercury (THg) in their livers (geo. means 134.8μg/g wet weight (ww), 43.7 and 13.5, respectively) and kidneys (69.4, 11.1 and 6.1, respectively). Apparently tolerance of these concentrations was possible due to a threshold-dependent demethylation coupled with sequestration of resultant IoHg. Demethylation and sequestration processes also appeared to have reduced the amount of MeHg redistributed to eggs. However, the relatively short time spent by adults in the contaminated area before egg laying was also a factor in lower than expected concentrations of mercury in eggs. Most eggs (100% MeHg) had concentrations below 0.80μg/g ww, the putative threshold concentration where reproductive problems may be expected; there was no conclusive evidence of mercury-related depressed hatchability. After hatching, the young birds were fed diets by their parents averaging 0.36–1.18μgMeHg/g ww through fledging. During this four to six week period, accumulated mercury concentrations in the organs of the fledglings were much lower than found in adults, but evidence was detected of toxicity to their immune (spleen, thymus, bursa), detoxicating (liver, kidneys) and nervous systems. Several indications of oxidative stress were also noted in the fledglings and were most apparent in young cormorants containing highest concentrations of mercury. This stress was evidenced by increased thiobarbituric acid-reactive substances, low activities of enzymes related to glutathione metabolism and low levels of reduced thiols, plus an increase in the ratio of oxidized to reduced glutathione. At lower concentrations of mercury, as was found in young egrets, we observed elevated activities of protective hepatic enzymes, which could help reduce oxidative stress. Immune deficiencies and neurological impairment of fledglings may affect survivability when confronted with the stresses of learning to forage and the ability to complete their first migration.

METHYLMERCURY ACCUMULATION IN TISSUES AND ITS EFFECTS ON GROWTH AND APPETITE IN CAPTIVE GREAT EGRETS

To test the hypothesis that fledging wading birds would be more at risk from mercury toxicosis than younger nestlings, captive great egret nestlings were maintained as controls or were dosed from 1- to 14-wk-old with 0.5 or 5 mg methylmercury chloride/kg wet weight in fish. Birds dosed with 5 mg/kg suffered from subacute toxicosis at wk 10–12. Growing feather concentrations were the most closely correlated with cumulative mercury consumed per weight. Blood concentrations of mercury increased more rapidly after 9 wk in all groups when feathers stopped growing. Total mercury accumulated in tissues in concentrations in the following order: growing scapular feathers > powderdown > mature scapular feathers > liver > kidney > blood > muscle > pancreas > brain > bile > fat > eye. The proportion of total mercury that was methylated depended upon tissue type and dose group. Selenium accumulated in liver in direct proportion to liver mercury concentrations. After wk 9, appetite and weight index (weight/bill length) declined significantly in both dosed groups. At current exposure levels in the Everglades (Florida, USA) mercury deposited in rapidly growing feathers may protect nestlings from adverse effects on growth until feathers cease growing.

Histologic, neurologic, and immunologic effects of methylmercury in captive great egrets.

Captive great egret (Ardea albus) nestlings were maintained as controls or were dosed with methylmercury chloride at low (0.5), and high doses (5 mg/kg, wet weight) in fish. Low dosed birds were given methylmercury at concentrations comparable to current exposure of wild birds in the Everglades (Florida, USA). When compared with controls, low dosed birds had lower packed cell volumes, dingy feathers, increased lymphocytic cuffing in a skin test, increased bone marrow cellularity, decreased bursal wall thickness, decreased thymic lobule size, fewer lymphoid aggregates in lung, increased perivascular edema in lung, and decreased phagocytized carbon in lung. High dosed birds became severely ataxic and had severe hematologic, neurologic, and histologic changes. The most severe lesions were in immune and nervous system tissues. By comparing responses in captive and wild birds, we found that sublethal effects of mercury were detected at lower levels in captive than in wild birds, probably due to the reduced sources of variation characteristic of the highly controlled laboratory study. Conversely, thresholds for more severe changes (death, disease) occurred at lower concentrations in wild birds than in captive birds, probably because wild birds were exposed to multiple stressors. Thus caution should be used in applying lowest observed effect levels between captive and wild studies.

Mercury in livers of wading birds (ciconiiformes) in southern Florida

Mercury was measured in livers from 144 wading birds representing seven species collected from four different areas in southern Flordia, including the Everglades National Park. Significant differences in hepatic mercury concentrations were identified between birds collected from different geographic locations, birds of different ages, dietary factors, and relative amounts of body fat. Birds collected from an area encompassing the central Everglades and eastern Florida Bay had significantly greater concentrations of hepatic mercury than did birds from other collection areas. Livers from fledgling and young adult birds contained approximately three times the concentration of mercury as livers from nestling birds. Bird species whose prey base consists of larger fish were found to have approximately four times the hepatic concentration of mercury as did those species which consume smaller fish or crustaceans. Birds with minimal to moderate amounts of body fat had two to three times the concentration of hepatic mercury as birds with relatively abundant body fat reserves. Four great blue herons collected from the central Everglades contained liver mercury at concentrations typically associated with overt neurologic signs (⩾30 μg/g). Between 30% and 80% of potential breeding-age birds collected from this area contained hepatic mercury at concentrations associated with reproductive impairment in ducks and pheasants. These data suggest that declining numbers of nesting ciconiiform birds in Florida may be due, in part, to mecury contamination of their food supply.

Mercury and cause of death in great white herons

Mercury contamination is suspected to adversely affect wading birds in southern Florida. To determine the magnitude of contamination associated with cause of death we followed 3 adult and 19 juvenile radio-tagged great white herons (Ardea herodias occidentalis), recovered them soon after death, and determined liver mercury content and cause of death. Birds that died from acute causes had less (P 25 ppm wm liver mercury. Although detrimental to the health of wading birds, mercury contamination is presumably more detrimental to their reproductive efforts; therefore, an understanding of its ill effects is important in the management of these birds. 29 refs., 1 fig.

Effects of methylmercury exposure on the immune function of juvenile common loons (Gavia immer)

We conducted a dose-response laboratory study to quantify the level of exposure to dietary Hg, delivered as methylmercury chloride (CH3HgCl), that is associated with suppressed immune function in captive-reared common loon (Gavia immer) chicks. We used the phytohemagglutinin (PHA) skin test to assess T-lymphocyte function and the sheep red blood cell (SRBC) hemagglutination test to measure antibody-mediated immunity. The PHA stimulation index among chicks receiving dietary Hg treatment did not differ significantly from those of chicks on the control diet (p = 0.15). Total antibody (immunoglobulin [Ig] M [primary antibody] + IgG [secondary response]) production to the SRBC antigen in chicks treated with dietary methylmercury (MeHg), however, was suppressed (p = 0.04) relative to chicks on control diets. Analysis indicated suppression of total Ig production (p = 0.025 with comparisonwise alpha level = 0.017) between control and 0.4 microg Hg/g wet food intake treatment groups. Furthermore, the control group exhibited a higher degree of variability in antibody response compared to the Hg groups, suggesting that in addition to reducing the mean response, Hg treatment reduced the normal variation attributable to other biological factors. We observed bursal lymphoid depletion in chicks receiving the 1.2 microg Hg/g treatment (p = 0.017) and a marginally significant effect (p = 0.025) in chicks receiving the 0.4 microg Hg/g diet. These findings suggest that common loon chick immune systems may be compromised at an ecologically relevant dietary exposure concentration (0.4 microg Hg/g wet wt food intake). We also found that chicks hatched from eggs collected from low-pH lakes exhibited higher levels of lymphoid depletion in bursa tissue relative to chicks hatched from eggs collected from neutral-pH lakes.

The epizootiology of eustrongylidosis in wading birds (Ciconiiformes) in Florida.

A total of 2,167 individuals representing 15 species of wading birds was examined for infection with the nematode Eustrongylides ignotus in Florida (USA). Ten of the species were infected with the greatest prevalences occurring in great blue herons (Ardea herodius) (33%), great egrets (Casmerodius albus) (22%), and snowy egrets (Egretta thula) (19%). Among nestlings, prevalences increased with age. This parasite was estimated to cause at least 80% mortality among nestling ciconiiforms at one colony in Everglades National Park, and was found in 15% of nestling ardeids throughout the state. Despite wide sampling efforts, infected fish (second intermediate hosts) were only found at six sites in Florida, all of which had been physically altered, such as with canals and ditches, and had an anthropogenic (human-caused) source of nutrient pollution. Colonies near sources of infected fish experienced significantly higher prevalences of eustrongy-lidosis than did colonies for which no source of infected fish could be found within 20 km. Higher prevalences were found at freshwater and estuarine mainland colonies than at marine colonies. Densities of aquatic oligochaetes, which may act as first intermediate hosts, were highest at sites containing infected fish and at sites with a source of nutrient pollution. Conservation and management of wading bird species should include consideration of this disease, epizootics of which seem to be linked to nutrient pollution.

Diseases of Poultry, 12th Edition

The 12th edition of Diseases of Poultry is a ‘‘must have’’ reference for those involved in avian diagnostics, and it continues to be a basic foundation for those engaged in avian disease research. First published in 1943, Diseases of Poultry has been reissued every four to seven years. I started with the 8th edition and have never questioned my purchase of each subsequent edition. Over 65 years of publication, the editors, contributors, and chapters have been refined, reshuffled, added to, and evolved—some of them more than others. The current impressive list of 96 contributing authors includes dozens of familiar names in the wildlife disease arena. The bulk of its 1,323 pages—weighing in at close to five pounds on my (very inaccurate) bathroom scale—will keep one fit, if handled daily. Although I have relied on this reference for many years, in reviewing the new edition, I was surprised to find that the first two chapters contain a rather thorough compilation of information about the principals of disease diagnosis, prevention, epidemiology, and treatment of poultry—information that would be useful to individuals involved in the housing of wild birds used in research and also to researchers unfamiliar with the poultry industry. The first chapter covers invaluable, up-todate information on such topics as biosecurity, coping with sources of infection, necropsy techniques and sample collection, quarantine, housing, feeding, and data interpretation. An introduction to avian immunology, expanded with this edition into a separate chapter, covers host factors for disease resistance. Because the domestic chicken is second only to the mouse among animals studied for health research, this extensive compilation of existing knowledge on diseases impacting chickens around the world is especially useful—it may be the best single source of methodology and results available. In many chapters, the host section provides a brief list of wild bird species that share the diseases; however, the coverage of wild birds varies between chapters. Thus, this reference provides an excellent foundation for the understanding of a disease, but readers seeking extensive information about its application to wild birds will require supplemental references. The kind of detailed information available for each of the roughly 120-plus diseases is clearly illustrated by the list of sections and subheadings in the chapter on pox, as one example. The introduction gives a definition of the disease, synonyms, economic significance, and public health significance. A history of the disease is followed by information on etiology, morphology, chemical composition, viral replication, and susceptibility to chemical and physical agents. The strain classification includes subheadings of polypeptides and genomic differences in avian pox viruses, as well as nonessential and immunomodulatory genes. A section on laboratory host systems addressing birds, avian embryos, cell culture, cytopathic effects, and plaque formation is followed by pathology and epidemiology, incidence and distribution, natural and experimental hosts, transmission, incubation period and clinical signs, morbidity and mortality, and pathology (gross and microscopic and ultrastructural). Following the natural history of pox, the chapter provides a section on diagnosis, with subheadings of microscopy, isolation and identification of virus (bird inoculation, avian embryo inoculation, and cell culture), serology and protection tests—including immunodiffusion, passive hemagglutination, neutralization, florescent antibody, immunoperoxidase, ELISA, immunoblotting, molecular methods (restriction endonuclease analysis of avian pox virus DNA, Journal of Wildlife Diseases, 45(1), 2009, pp. 251–256 # Wildlife Disease Association 2009

SUBCHRONIC EFFECTS OF METHYLMERCURY ON PLASMA AND ORGAN BIOCHEMISTRIES IN GREAT EGRET NESTLINGS

In recent years, high concentrations of mercury have been found in wading birds in Florida, USA. Great egret (Ardea alba) chicks (2 weeks old) were dosed orally daily with the equivalent of 0, 0.5, or 5 microg/g Hg as methylmercury chloride in the diet for up to 12 weeks. Weakness of the legs or paralysis occurred in all high-dosed birds. Geometric mean blood Hg concentrations were 0.17, 10.3, and 78.5 microg/g (wet wt), respectively. Mercury concentrations for organs (microg/g wet wt), including brain (0.22, 3.4, and 35, respectively), liver (0.34, 15.1, 138, respectively), and kidney (0.28, 8.1, and 120, respectively), increased in a dose-dependent manner. Total glutathione (GSH) peroxidase activity was significantly lower in the plasma, brain, liver, and kidney of the high-dosed group. Plasma aspartate aminotransferase activity increased with mercury treatment, whereas lactate dehydrogenase activity decreased. Four other plasma chemistries were decreased significantly in the high-dosed group and included uric acid, total protein, albumin, and inorganic phosphorus. Lipid peroxidation increased in liver (low and high dose) and brain (high dose). Tissue changes in concentrations of reduced thiols included decreased total thiols and protein-bound thiols in liver, decreased protein-bound thiols in kidney, and increased GSH in kidney and brain. Activities of GSH S-transferase and oxidized glutathione reductase increased in liver. In kidney, GSH S-transferase and glucose-6-phosphate dehydrogenase activities increased with mercury dose. These findings, including apparent compensatory changes, are compared to other Hg studies where oxidative stress was reported in egrets, herons, and diving ducks in the field and mallards in the laboratory.

FEEDING PATTERNS AND AGGRESSIVE BEHAVIOR IN JUVENILE AND ADULT AMERICAN FLAMINGOS

We studied the feeding and aggressive behavior of adult and juvenile American Flamingos (Phoenicopterus ruber ruber) at a coastal salina in Venezuela. Most birds fed in large flocks in early morning, roosted at mid-day, and resumed feeding in late afternoon- early evening. Flamingos rarely flew, except when disturbed. Adults in our study stepped at the same rates while feeding as did Chilean Flamingos (P. chilensis) feeding in the Chilean and Bolivian Andes. Paired observations of birds within mixed-age flocks revealed that adults stepped more during feeding bouts, but less between bouts, and spent more time overall with their bills in the water filter-feeding, than did juveniles. We calculate that the food-intake rate of juveniles was, at most, 82% that of adults. Both adults and juveniles walk-fed and stamp-fed. Juveniles, but not adults, were twice as likely to be supplanted when stamp-feeding than when walk-feeding. Juveniles were more often involved in ag- gression, especially as recipients, than were adults. Aggressive encounters significantly af- fected the amount of time flamingos spent filter feeding.