Wildlife and Landscape Science News

Summer 2010

Wildlife Populations

Habitats and Ecosystems

Health Effects of Toxics

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Wildlife Populations

> First rangewide genetic study of golden winged warblers reveals few pure populations

Golden-winged warbler | Photo: Carl SavignacThere are far fewer genetically pure populations of the threatened golden-winged warbler - a species of global conservation concern - than previously thought, having important implications for those working in species at risk conservation, according to a recent study.

According to the published results, genetically pure populations of golden-winged warblers may only exist in Manitoba, which, according to population estimates by Partners In Flight, constitutes only one per cent of the global breeding population.

Researchers found it “very disturbing” to identify introgression in Minnesota, where 40 per cent of the global population breeds, and where the bird is not afforded any protection.

Researchers examined the genetics from 608 golden-winged warblers, and 145 blue-winged warblers, across nine U.S. states and three Canadian provinces to provide the first range-wide assessment of mitochondrial DNA (mtDNA) introgression between the golden-winged warbler and the blue-winged warbler. This is an important first step to examine pattern, level, rate and direction of gene flow between the two species and better inform conservation activities.

The study showed populations from New York displayed the highest levels of introgression, followed by mid-Wisconsin and Tennessee. All states and provinces had some level of introgression except Manitoba and Quebec.

Although scientists do not yet fully know how hybridization affects the species’ demography, they say hybridization is commonplace and typically leads to the local extirpation of golden-winged warblers.

Since 1966, an estimated 64 per cent of the global population has been lost, making it one of the fastest declining passerine species in North America. In response, it was listed in 2006 as a federally threatened species in Canada.

Although not federally listed in the U.S., the bird is listed as endangered in Indiana, Ohio, and Massachusetts; as rare or threatened in North Carolina, Maryland, Vermont and Kentucky; and considered a species of special concern in Wisconsin, Georgia, Connecticut, New Jersey and New York.

Work is underway to increase the sample size and geographic sampling area. Researchers have identified an important next step as the analysis of nuclear DNA, which is inherited from both parents, and would provide greater depth of understanding than mtDNA analysis alone, which is only inherited maternally.

Some initial findings from the most recent work indicate the genetically pure population of golden-winged warblers is even narrower than the published findings, occurring in only the most extreme limits of the breeding range in Manitoba.

This work, in combination with surveys and habitat modelling, is being used by the Golden-winged Warbler Working Group to identify which habitat requirements the bird prefers. This work has also contributed to a Recovery Strategy that is currently under development for the golden-winged warbler. Habitat manipulation to prevent gene-flow between the two “sister species” is one possible solution that might enhance the chance of species recovery efforts.

Source: Vallender, R., S.L. Van Wilgenburg, L.P. Bulluck, A. Roth, R. Canterbury, J. Larkin, R. Fowlds and I.J. Lovette. 2009. Extensive rangewide mitochondrial introgression indicates substantial cryptic hybridization in the golden-winged warbler (Vermivora chrysoptera). Avian Conservation and Ecology (2)4.

Contact: Steve Van Wilgenburg (306) 975-5506 or Rachel Vallender (819) 953-3296


> Relaxation of hunting restrictions does not reduce snow goose populations, waterfowl managers encouraged to re-evaluate strategy

A recent study suggests that decade-long efforts to reduce the midcontinent population of lesser snow geese did not achieve desired effects.

Hunter with geese | Photo: Ray Alisauskas, Environment CanadaStarting in 1999, hunters were given unprecedented opportunity to hunt different populations of light geese (i.e., Ross's geese, greater and lesser snow geese) in portions of Canada and the U.S., because of the damage they were causing to terrestrial and saltmarsh ecosystems in the central and eastern Canadian Arctic and sub Arctic regions of Hudson Bay.

Despite extended hunting opportunities (including harvest during spring), the use of previously prohibited equipment, and no daily harvest or possession limits over much of North America, the midcontinent population of lesser snow geese continued to grow during these conservation measures, albeit at a reduced rate, say the study authors. 

For 10 years before then, waterfowl managers had been incrementally liberalizing hunting regulations in response to rapidly increasing abundance of light geese, but out of growing concern for Arctic ecosystems, the Arctic Goose Management Initiative recommended in 1997 that the annual harvest of midcontinent snow geese increase by three times, to a target of 2.2 million birds. Regulations were adjusted to accommodate more harvest.

Annual harvest of the midcontinent population peaked at one million geese only twice shortly after the special measures. In this short time those figures were insufficient to have an effect on overall snow goose survival, and population size of the midcontinent region. Another study of abundant greater snow geese that stage along the St. Lawrence River in spring and fall suggested that increased harvest was initially successful in reducing population levels, but population growth had resumed after decreased hunting effort and success.

Reduced numbers of hunters participating in spring harvest contributed to low harvest of lesser snow geese, and harvests were not sufficient to offset the population increase. Researchers also suggest the birds may have become wary and adapted behaviours to avoid vulnerability.

Increased hunting pressure may have reduced the ability of geese to fatten during spring and to nest in the Arctic, and thereby reduce the numbers of goslings produced per adult, but it remains unclear whether hunting pressure, or other factors, caused declines in annual production of young, say researchers.

Photo of snow geese in abundant population | Photo: Ray Alisauskas, Environment CanadaResearchers point out that historically, growth rates of geese have increased because of their ability to survive, fueled by agricultural production on wintering grounds and along migration routes.

In order to reduce populations of geese and protect fragile Arctic ecosystems, the authors offer several options for goose managers to consider.

First, the current measures could remain in place and be considered as a suite of tools available for attempting to reduce the numbers of geese in the long-term. Second, where they have not already been addressed, hunting restrictions on light geese in Canada could be further relaxed as they are in the U.S. Specifically, harvest of Ross’s geese in the spring, currently prohibited in Canada, could be allowed, as this population continues to increase even faster than snow geese. Third, direct control of geese and eggs where appropriate. Finally, active recruitment of snow and Ross's goose hunters might be increased through subsidization of hunting licenses and/or legalization of commercial trade in harvested light geese.

Researchers suggest that abundance of mid-continent snow geese was probably underestimated in the past, and may have contributed to overconfidence in the presumed ability of hunting pressure to reduce survival and cause population decline. They point to several additional avenues of research that will help to better understand goose-habitat interactions including inventory of suitable habitats for geese through remote sensing. They strongly recommend continued banding of geese in the Arctic to retain ability to monitor survival, distribution and continental abundance.

Source: Alisauskas R., et al. (in revision.) Effect of population reduction efforts on harvest, survival and population growth of midcontinent Snow Geese. Wildlife Monographs.

Contact: Ray Alisauskas (306) 975-4556


Habitats and Ecosystems

> Migrating birds at higher latitudes experience lower risk of nest predation

Average latitudinal decrease in nest predation risk and map of the shorebird breeding sites where artificial nests were monitored. The decrease in predation risk (3.6% per degree relative to the southernmost site, Akimiski Island) is indicated at 5° intervals on the latitudinal scale at right.

Average latitudinal decrease in nest predation risk and map of the shorebird breeding sites where artificial nests were monitored. The decrease in predation risk (3.6% per degree relative to the southernmost site, Akimiski Island) is indicated at 5° intervals on the latitudinal scale at right.

According to a new study recently published in Science, as migrating birds nest farther north, nest predation risk decreases, providing never before documented evidence that predation, much like food availability and risk of parasitic infection, may be a factor that influences the decision to migrate.

Environment Canada researchers, in partnership with previous Environment Canada students, found that for every one degree of increase in latitude, the relative risk of predation decreased by 3.6 per cent.

Researchers monitored 1555 artificial nests along a 3350 km latitudinal gradient from sub-Arctic to high-Arctic regions in Canada. They found that birds nesting on the southern most point of their study had an increased predation risk of 65 per cent over their most northern counterparts.

Predation has long been known as a driver in determining nest sites and clutch sizes, but this is the first time that it has been identified as a benefit for birds that pay high costs to migrate vast distances, some many thousands of kilometres.

Birds that nest at higher latitudes require large energetic and metabolic reserves and may be at risk of mortality from extreme weather events. According to this study, these costs may be compensated for by a reduced risk of nest predation.

In order to further explain these tradeoffs in bird life history strategies, researchers say they must compare ecological conditions on breeding grounds, reproductive components and adult survival so that they can better understand the evolution of long distance migration.

Researchers say that access to field stations, student collaboration and shared data sets are integral to reaching these findings.

This paper resulted from work conducted under the International Polar Year project “ArcticWOLVES (Wildlife Observatories Linking Vulnerable EcoSystems.”

Read a critique submitted to Science about the suitability of artificial nests and read the authors’ response to the letter.

Source: McKinnon, L., P.A. Smith, E. Nol, J.L. Martin, F.I. Doyle, K.F. Abraham, H.G. Gilchrist, R.I.G. Morrison and J. Bêty. 2010. Lower predation risk for migratory birds at high latitudes. Science 327(5963): 326-327. [DOI: 10.1126/science.1183010]

Source: Faaborg, J. 2010. Suitability of Artificial Nests. Science 328(5974): 46. [DOI: 10.1126/science.328.5974.46-a]

Source: McKinnon, L., et al. 2010. Suitability of Artificial Nests-Response. 2010. Science 328(5974): 46-47. [DOI: 10.1126/science.328.5974.46-b]

Contact: Paul Smith (613) 998-7362


Health Effects of Toxics

> Arctic wildlife and health effects of contaminants: a new assessment recently released

Polar bear | Photo: photos.comA new scientific assessment report reveals how contaminants are affecting the health of Arctic fish and wildlife, highlighting several ‘hot spots’ of concern, and recommending further areas of study for researchers.

The review, one of several for a 2010 report by the circumpolar Arctic Monitoring and Assessment Program (AMAP), summarizes new post-2002 data on the exposure and effects of persistent organohalogen contaminants (OHCs), including legacy and emerging compounds, and attempts to identify threshold contaminant levels in Arctic wildlife to evaluate health risks.

The assessment reports hot spot species and populations most at risk of OHC exposure are:

  • polar bears (East Greenland, Svalbard and West and South Hudson Bay populations)
  • killer whales (Alaska and Norway populations)
  • black-legged kittiwake, great and lesser black-backed gulls, and herring gulls (Northern Norway populations)
  • glaucous gulls (Svalbard populations)
  • ivory gulls (Canadian central-high Arctic)
  • northern fulmars (Svalbald and Canadian high Arctic populations)
  • ringed seals (East Greenland population)
  • stellar sea lions (Bearing Sea population)
  • Arctic char (Svalbard population)
  • Greenland shark

Killer whales | Photo: Corel CorporationResearchers found that although these species have exceeded a tissue concentration higher than the general level of concern of one part per million, there is no clear evidence that OHCs are causing population-level stress in all species.

To assess how these species might be affected at population levels, researchers considered contamination in a larger context of other complex interactions between natural and human-induced environmental, ecological and physiological stressors occurring in the Arctic, as these factors can influence exposure and effects of contaminants.

Disease, predation, climate change, food scarcity, body condition, as well as various spatial and temporal trends can influence how contaminants affect species at a population level. Researchers also say a complex cocktail of contaminants found in Arctic biota means that contaminants can act alone or in combination, and can undergo biotransformation in ways which make the metabolites more toxic than the original compound, adding to the complexity of factors.

Arctic fox | Photo: photos.comFor example, controlled studies involving sled dogs and Arctic foxes fed minke whale blubber and pork fat, have highlighted that OHCs adversely affect polar bear liver and kidney functions, immune response and endocrine system, which helps regulate growth, cognitive abilities, and body temperature. These impairments may alter the ability for bears to acclimatize and adapt to extreme Arctic environments.

When these effects are considered in combination with climate change, natural periods of fasting, cub survival rate, and female reproductive impairment, polar bear populations in East Greenland and Svalbard may be at higher risk of chronic population-level stress.

Similarly, OHC levels in glaucous gulls from Svalbard and the Eastern Russian Arctic have been associated with energy expenditure, nest attendance behaviour, thermoregulation and the ability to transfer heat to eggs during incubation.

Glaucous gull | Photo: USFWSFurther studies with great black-backed gulls from northern Norway have shown the effects of certain OHCs are aggravated when the birds are exposed to parasites, predation, pathogens, climate change, and food scarcity.

In general, OHC levels in fish did not raise concerns. One exception was a hot spot in Svalbard where Arctic char in a freshwater lake received a high load of contaminants from the guano in a nearby seabird colony. New experiments also indicate that OHCs can be redistributed from Arctic char fat stores to critical tissues, like the brain and liver, in response to seasonal long-term fasting.

Researchers point to several avenues of study that, if conducted, would help the scientific community better explain the complexity of the effects of contaminants on Arctic biota.

These include:

  • development of baseline ecological and physiological information for Arctic wildlife (e.g., hormones, vitamins, blood variables, immune factors, etc.) and other factors that may affect these (e.g., time of day/year, health status)
  • study of additional vulnerable or keystone species (e.g., ivory gull, great skua, ringed seal)
  • effects of OHCs during periods of physiological sensitivity (e.g., growth, reproduction, fasting periods.)
  • emerging contaminants
  • combined effects of OHCs and other anthropogenic and natural stressors

Researchers also recommend more collaboration between scientists with regard to studies on Arctic spatial and temporal trends, more harmonization of sample collection and storage, and consistent laboratory analysis in order to improve impact of scientific results.

Source: Letcher, R.J., J.-O. Bustnes, R. Dietz, B.M. Jenssen, E.H. Jørgensen, C. Sonne, J. Verreault (Post Doctoral Fellow), M. Vijayan and G.W. Gabrielsen. 2009. Exposure and effects assessment of persistent organic pollutants in Arctic wildlife and fish. Sci. Total Environ. Avalable online.

Contact: Dr. Robert Letcher (613) 998-6696


> Outdoor study using native species shows low concentrations of common pesticide turns male frogs into females

One of the most commonly used pesticides in the world appears to turn male northern leopard frogs into female frogs and slows metamorphosis, according to a recent study conducted by researchers from the University of Ottawa in collaboration with Environment Canada and Health Canada.

Northern leopard frog | Photo: Ryan BoltonThe team found that the herbicide atrazine could trigger the feminization of northern leopard frogs at concentrations of just 1.8 parts per billion (ppb). At this low concentration, there were 20 per cent more females present compared with controls. However, without easy genetic sexing of these frogs, the researchers had no way to confirm the number of true females versus the number of males that appeared as females based on the gross morphology of their gonads.

The researchers also gathered evidence that atrazine exposure affected the hypothalamic-pituitary-thyroid axis in the tadpoles. This axis helps regulate development, and the team found that at least half of the exposed tadpoles were unable to metamorphose into juvenile animals by the end of the experiment. Survival was also significantly lower in the 1.8 ppb treatment tanks compared to the control tanks.

The study used native species in outdoor tanks, with natural debris and exposure to the elements, to mimic how the frogs might be exposed in the wild. The study design sought to reduce criticisms that laboratory experiments with non-native species in laboratory aquariums are not relevant to assess potential effects stemming from exposure of native species under actual environmental conditions.

Researchers added 30 tadpoles to each of five tanks that received a treatment: one group of tanks was a clean water control, another group contained atrazine concentrations of 0.1 ppb, and another group contained concentrations of 1.8 ppb. The tanks were filled with well water to avoid any atrazine contamination, and atrazine was added to the treatment tanks as two “pulses” in May following Canadian agricultural spray practice. The tadpoles were left to develop naturally in the tanks over the summer until the test ended in September.

The researchers found that atrazine affected the frogs through multiple pathways. For instance, those frogs exposed to the highest atrazine concentration experienced alterations in gene expression in their brains that could possibly make the animals more sensitive to the female hormone estrogen, and lead to other physiological changes. Since many species respond to hormone signals in a similar manner as amphibians, the study has potential implications for those studying other taxonomic groups.

Recently, much attention has been paid to atrazine and the effects on amphibians, with one recent study published in the Proceedings of the National Academy of Sciences discussing how atrazine turned some male African clawed frogs into functioning females that copulated with unexposed males and produced viable eggs.

Atrazine is commonly used for weed control in crops including corn, and is ubiquitous in surface water, groundwater and precipitation. Surface water concentrations can exceed criteria for freshwater aquatic life and drinking water; in the midwestern United States atrazine concentrations have been found to exceed 200 ppb in streams and rivers, the surface waters typically monitored for pesticide residues.

Scientists have yet to determine the potential implications of wide-scale atrazine exposure on global amphibian populations and whether there are population-level effects. More generally, research on contaminants and amphibians is needed to better inform contaminant policies, guideline development and recovery efforts, and to determine if amphibians are being adequately protected by pollution prevention regulations.

Source: Langlois, V.S., A.C. Carew, B.D. Pauli, M.G. Cooke and V.L. Trudeau. 2010. Low levels of the herbicide atrazine alter sex ratios and reduce metamorphic success in Rana pipiens tadpoles raised in outdoor mesocosms. Environmental Health Perspectives 118: 552-557.

Source: Hayes, T.B. et al. 2010. Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). PNAS. Available online March 1.

Source: Lazorko-Connon, S., and G. Achari. 2009. Atrazine: its occurrence and treatment in water. Environ. Rev. 17: 199-214.

Contact: Bruce Pauli (613) 998-6690


> Intercontinental studies of river birds reveal implications for measuring contaminants in eggs

Image of freshwater ecosystem | Photo: photos.comRecent studies examining changes in the diet of two dippers - species of songbirds that catch their food underwater in fast flowing streams - highlight how local environmental conditions can alter foraging behaviour and affect egg contaminant composition, having implications in contaminant pathway analysis.

Using traditional dietary and modern stable isotope analysis, scientists examined the blood, feces, prey and eggs of American dippers from salmon-rich British Columbia rivers and compared them to Eurasian dipper samples collected from rural Welsh rivers with varying acidity.

Even though the dipper species have similar ecology, they displayed different contaminant loadings. Scientists determined that female dippers in both locations altered foraging patterns to accommodate changing nutritional requirements during egg-laying, and that the different local conditions caused different food availability and subsequent contaminant pathways in the two closely related species.

American dippers, even though they fed at a higher trophic level with a diet rich in fish, generally did not have a higher burden of contaminants compared to their Eurasian counterparts. Organochlorines like mirex and dieldrin appeared to be absent in American dipper eggs, but appeared in 86 per cent of Eurasian dipper eggs at acidic sites, despite a 1989 European ban. However, mercury levels were higher in American dippers, albeit at levels that didn’t pose risks to reproduction, because of their reliance on fish in their egg-laying diet. The two species had similar polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE) levels with similar congeners.

Stable isotope analysis in plasma and red blood cells allowed researchers to determine recent diet, within the past four days, and compare it to past diet, over 30 days. Although it has been shown that blood can reveal dietary changes, few studies have validated this technique or used it in combination with traditional dietary analysis. The researchers say the corroborating data from both methods allows for more confidence in the results.

Dippers were examined because they are good indicators for freshwater ecosystems and are used in monitoring programs to examine mercury, selenium, PCB and organochlorine pesticide levels. It is often assumed that birds’ eggs reflect local contaminant conditions, but this study examined the more complex spatial and temporal variations and interactions that might affect contaminant loadings.

Source: Morrissey, C.A., J.E. Elliott and S.J. Ormerod. 2009. Diet shifts during egg laying: Implications for measuring contaminants in bird eggs. Environmental Pollution. Published online.

Source: Morrissey, C.A., J.E. Elliott and S. J. Ormerod. 2010. Local to continental influences on nutrient and contaminant sources to river birds. Environmental Science and Technology. Available online.

Contact: John Elliott (604) 940-4680


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