2004 Progress Report: Evaluating the Impact of Multiple Stressors on Common Loon Population Demographics - An Integrated Laboratory and Field Approach

EPA Grant Number: R829085
Title: Evaluating the Impact of Multiple Stressors on Common Loon Population Demographics - An Integrated Laboratory and Field Approach
Investigators: Meyer, Michael W.
Institution: Wisconsin Department of Natural Resources
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 2001 through March 31, 2005 (Extended to November 25, 2005)
Project Period Covered by this Report: October 1, 2003 through March 31, 2004
Project Amount: $490,759
RFA: Wildlife Risk Assessment (2001) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Ecosystems , Biology/Life Sciences


In this research project, an intensive effort is being focused on collecting information on the abundance, distribution, and health of common loons inhabiting a risk assessment region of Wisconsin, where their breeding habitat (i.e., lakes and reservoirs) vary in mercury (Hg) contamination, degree of habitat alteration, and human recreational use. A rigorous field sampling scheme was used to produce a random sample of loon breeding pairs from which the common loon population density and critical population demographic parameters (adult survival, fecundity, and juvenile recruitment) on the breeding grounds are being calculated. Concurrently, the impact of stressors on these parameters was quantified. Several stressors are likely associated with impacts on loon demographic parameter, including mercury exposure, habitat quality, and human disturbance.

The overall objectives of this research project are to conduct research to improve predictions of loon population dynamics in regions impacted by multiple stressors, and to advance techniques for assessing the relative risk of Hg exposure and other stressors on loon populations in the Upper Midwest United States. The specific objectives of this research project are to: (1) estimate the population size of adult common loons in a 8,600 km2 region of northern Wisconsin impacted by Hg deposition, habitat alteration, and human disturbance; (2) quantify loon population demographic parameters within this study area, including adult survival, fecundity, and juvenile recruitment rates; (3) assess the impact of stressors (Hg exposure, habitat alteration, human disturbance) on the measured demographic parameters via projection matrix models; and (4) construct habitat models that evaluate the relationship between lake and shoreline habitat parameters and measures of loon lake use and reproductive success.

The expected results include a site-specific Wisconsin Common Loon Population Model, which predicts population growth rates as a function of estimates of loon population abundance, demographics parameters, and impacts of stessors on these parameters within the risk assessment region.

Progress Summary:

Field surveys were conducted from May 1 to September 30 in 2002, 2003, and 2004, to estimate the loon population density and population demographic parameters (adult survival, fecundity, and juvenile recruitment) within the area of risk. GIS tools were used to create a 8,600 km2 sample grid that was subdivided into 344 25-km2 cells. Cells were stratified into four categories of loon nesting habitat quality based on surface water area. Cells randomly selected (22 in 2002, 32 in 2003, and 36 in 2004) from each strata and all lakes greater than 4 ha within or intersected by the cells were surveyed to count and map the number and location of loons present. There are a total of 1,582 waterbodies greater than 4 ha within the study area. The dual frame sampling method is used to estimate population abundance, and demographic parameters (adult survival, juvenile recruitment, fecundity) are estimated via additional surveys. The impact of stressors on demographic parameters are assessed via response curves and integrated into the population model to evaluate potential impacts on population growth rates. Hg risk is established on the basis of exposure and thresholds of effect. Exposure has been measured via field tissue samples and/or predicted by laboratory-derived pharmacokinetic models and compared to thresholds of effect. Effect thresholds are established via controlled dosing studies in the laboratory and field correlations of Hg exposure and reproduction. Loon habitat models are being constructed to evaluate habitat alterations associated with human population growth. Spatially explicit variables such as shoreline housing densities, human population density, and proximity of housing to nest habitat are incorporated into the model, as are lake morphometry and water chemistry and clarity. Shoreline habitat is mapped into categories of nest habitat quality. An index of human-related disturbance rate also is developed.

In 2002, 22 randomly selected cells (6% of study area, 106 lakes) and 12 list segments (60 loon territories present in 2001) were surveyed; 120 adults were observed within the randomly selected cells, and 100 were categorized as territorial adults (83.3%) based on persistent presence and behaviors observed (2 adults exhibiting courtship/nesting/pair-bonded behavior) during more than 50 percent of population or nest monitoring surveys May 1 - June 15, 2002. Forty-nine of 106 (46%) lakes within the cells were occupied by territorial pair in 2002. In 2003, we surveyed 32 randomly selected cells (9% of study area, 139 lakes) and 12 list segments (60 lakes known to have pairs present in 2001 and 2002). Two-hundred thirty four adult loons were observed on the randomly selected lakes during the third period of Survey 1 (May 20-31), and 190 were categorized as territorial adults (81%) based on exhibitions of courtship and nesting behavior, similar to 2002 (80%). Sixty one of 139 lakes (44%) had territorial pairs present in 2003, similar to 2002 (46%). In 2004, we surveyed 36 randomly selected cells (10% of study area, 186 lakes) and 12 list segments (60 lakes known to have pairs present in 2001-2003). Two-hundred fifty five adult loons were observed on lakes randomly selected in 2004 cells, and 177 were categorized territorial adults (70%) based on exhibitions of courtship and nesting behavior. This is considerably lower than in 2002 and 2003, when 80 percent of adults observed were classified as members of territorial pair. Ninety of 183 lakes (49%) had territorial pairs present in 2004, a proportion somewhat greater than that of lakes surveyed in 2003 (44%) and 2002 (46%). The 2004 estimated number of territorial adults present in the study area (687 ± 94) was substantially greater than in 2002 (550 ± 104) and 2003 (463 ± 54).

Vital rates were measured annually during 2002-2004. The adult survival rate averaged 92 percent, hatching rate was 0.27 female chicks/hen, chick survival to 6 weeks averaged 0.80, and survival from banding to age 3 years was 0.53. Inclusion of these preliminary rates into the Wisconsin Loon projection matrix model predicts an annual growth rate of 1.00, or a nearly stable population.

Hg exposure assessment shows that less than 10 percent of Wisconsin common loon adults (n = 116 sampled) and chicks (n = 122) have blood Hg concentrations associated with toxicity in the laboratory or the field. Chicks hatched from eggs with methylmercury (MeHg) concentrations comparable to that of some loons in Wisconsin, however, have shown developmental abnormalities and hatching deficits. The impact of exposure on the population model predictions will be assessed via response curves.

We recorded disturbance events at 38 loon territories where adult loons were rearing chicks on our study area in 2002, 38 territories in 2003, and 40 territories in 2004. Beginning in 2003, we began collecting disturbance rates at nest sites by passively observing incubating loons at 40 territories and adding an additional 56 nests in 2004. Multiple regression analysis will be used to explore the relationship between: (1) rates of disturbance and nest success; (2) rates of disturbance and loon chick survival; and (3) rates of disturbance and indices of anthropogenic impacts, including boating activity, shoreline housing density, and presence/absence of various shoreline developments (public boat landings, campgrounds, marinas, condominiums, etc.).

Loon habitat suitability models are being developed and tested using field data to assess the relative importance of natural and anthropogenic features in defining and predicting loon distribution, abundance, and productivity. This data will be used to establish the relationship between habitat features and loon presence/absence and reproductive performance. These relationships will be used to establish response curves between response variables associated with demographic models and anthropogenic habitat features (housing density/proximity) and disturbance rates. Finally, the data will be used to estimate the carrying capacity of the study area and predict whether additional human settlement will impact carrying capacity. A variety of statistical techniques are used to quantify relationships between local characteristics, including anthropogenic stressors such as mercury and land use, and the presence and fecundity of loon pairs. Data was collected at 106 lakes in 2002, 139 lakes in 2003, and 186 lakes in 2004.

Future Activities:

We will complete the Wisconsin Common Loon Population Model, Wisconsin Common Loon Hg Exposure Model, and Wisconsin Common Loon Habitat Model in the spring of 2006. Final results of 3 years of common loon mercury dosing experiments also will be available in the spring of 2006. Finally, pilot studies have been conducted to develop methodology and dosing protocols for a common loon/MeHg egg injection study to be conducted in the field season in 2006, pending funding.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 12 publications 4 publications in selected types All 4 journal articles
Type Citation Project Document Sources
Journal Article Fevold BM, Meyer MW, Rasmussen PW, Temple SA. Bioaccumulation patterns and temporal trends of mercury exposure in Wisconsin common loons. Ecotoxicology 2003;12(1-4):83-93. R829085 (2002)
R829085 (2004)
  • Abstract from PubMed
  • Abstract: SpringerLink Abstract
  • Journal Article Fournier F, Karasov WH, Kenow KP, Meyer MW, Hines RK. The oral bioavailability and toxicokinetics of methylmercury in common loon (Gavia immer) chicks. Comparative Biochemistry and Physiology-A: Molecular & Integrative Physiology 2002;133(3):703-714. R829085 (2002)
    R829085 (2004)
  • Abstract from PubMed
  • Full-text: Wisconsin University Full-Text PDF
  • Abstract: Science Direct HTML
  • Journal Article Fournier F, Karasov WH, Meyer MW, Kenow KP. Daily energy expenditures of free-ranging common loon (Gavia immer) chicks. The Auk 2002;119(4):1121-1126. R829085 (2002)
    R829085 (2004)
  • Abstract: BioOne Abstract
  • Other: Wisconsin University
  • Journal Article Kenow KP, Gutreuter S, Hines RK, Meyer MW, Fournier F, Karasov WH. Effects of methyl mercury exposure on the growth of juvenile common loons. Ecotoxicology 2003;12(1-4):171-182. R829085 (2002)
    R829085 (2004)
  • Abstract from PubMed
  • Abstract: SpringerLink Abstract
  • Supplemental Keywords:

    methylmercury exposure, habitat alteration, prey abundance, human disturbance, stressors, demographics, EPA Region 5, Wisconsin, WI, survival, fecundity, recruitment, population size,, RFA, Scientific Discipline, Toxics, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecology, exploratory research environmental biology, wildlife, Ecosystem/Assessment/Indicators, Ecosystem Protection, HAPS, State, Ecological Effects - Environmental Exposure & Risk, Ecological Risk Assessment, Ecology and Ecosystems, 33/50, EPA Region, Mercury, predicting risk, demographic, ecological exposure, contaminants, demographic data, stressors, loon population demographics, multiple stressors, mercury & mercury compounds, Mercury Compounds, Wisconsin (WI), impact of stressors on loon population, Region 5, population

    Progress and Final Reports:

    Original Abstract
  • 2002 Progress Report
  • 2003
  • 2005
  • Final Report