2002 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, 2001 through March 31, 2002
Project Amount: $490,759
RFA: Wildlife Risk Assessment (2001) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Ecosystems , Biology/Life Sciences


The overall goals of this research project are to: (1) conduct research to improve predictions of loon population dynamics in regions impacted by multiple stressors; and (2) advance techniques for assessing the relative risk of Hg exposure and other stressors on loon populations in the upper Midwestern United States. The following specific objectives have been established to achieve those overall goals:

  • Estimate the population size of adult common loons in a 8,575 km2 region of northern Wisconsin impacted by Hg deposition, habitat alteration, and human disturbance.
  • Quantify loon population demographic parameters within this study area including adult survival, fecundity, and juvenile recruitment rates.
  • Assess the impact of stressors (Hg exposure, habitat alteration, human disturbance) on the measured demographic parameters.
  • Construct habitat models by developing relationships between lake and shoreline habitat parameters and measures of loon lake use and reproductive success.

The expected results include a Common Loon Demographic Model, which provides output-predicting population growth rates as a function of estimates of loon population abundance, demographic parameters, and impacts of stressors on these parameters.

Progress Summary:

Field surveys were conducted from May 1 to September 30, 2002, to estimate loon population density and population demographic parameters (adult survival, fecundity, and juvenile recruitment) within the area of risk. Geographic information system (GIS) tools were used to create an 8,575 km2 sample grid, which was subdivided into 343 25-km2 cells. 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 the potential impacts on population growth rates.

2002 Adult Loon Population Estimate

In 2002, we surveyed 22 randomly selected cells (7 percent of study area, 103 lakes) and 12 list segments (60 lakes known to have pairs present in 2001). One hundred and twenty adults were observed within the randomly selected cells and 65 percent of the lakes within the cells were occupied by territorial pairs. The breeding adult loon population within our study area was estimated to be 1,865 ±931 standard deviation (SD) in 2002. This level of precision is less than desired and calculations were made to determine the sample size necessary to increase the precision for 2003 and 2004. We determined that the 2002 estimate would have had a SD of ±252 if similar variance and 44 cells were surveyed (13 percent of study area) and ±105 if 66 cells were surveyed (19 percent of study area). We will attempt to accomplish this level of survey during the 2004 field season.

2002 Estimate of Wisconsin Common Loon Demographic Model Parameters

The 2002 estimate of demographic parameters for the Wisconsin Common Loon Demographic Model as represented by the following equation:

N(i+1) = sANiBi + HPscsj N(i+1-k) Bi

includes N = 1,865 (estimated number of breeding adults), sA = 0.91 (adult survival), B = 0.47 (proportion of adults nesting), H = 0.44 (egg hatching rate), P = to be determined (renesting potential), sc = 0.67 (chick survival), sj = 0.53 (juvenile recruitment), and k = 5 (age in years at first breeding). These parameters will again be estimated in 2003 and 2004. Deterministic and stochastic matrix population models, which are structured by age, will be used to project the population size and calculate the population growth rates for given survival and reproductive rates.

Quantification of Stressor Impacts: Hg Exposure Assessment

Development of Hg Bioaccumulation Model. We compared the toxicokinetics of methylmercury in captive common loon chicks during two time intervals to assess the impact of feather growth on the kinetics of mercury. We also determined the oral bioavailability of methylmercury during these trials to test for age-related changes. The blood-concentration time curves for individuals dosed during feather development (initiated 35 days posthatch) were best described by a one-compartment toxicokinetic model with an elimination half-life of 4 days. The data for birds dosed following completion of feather growth (initiated 84 days posthatch) were best fitted by a two-compartment elimination model that includes an initial rapid distribution phase with a half-life of 0.9 days, followed by a slow-elimination phase with a half-life of 116 days. We determined the oral bioavailability of methylmercury during the first dosing interval by comparing the ratios of the area under the blood-concentration time curves () for orally and intravascularly dosed chicks. The oral bioavailability of methylmercury during the first dosing period was 0.83, and did not appear to differ from the bioavailability estimate for the second dosing period. The results highlight the importance of feather growth on the toxicokinetics of methylmercury. We also have completed the determination of loon-field feeding rates and fish Hg levels in the risk-assessment area. These data and the kinetic rates provide the information needed to predict loon-Hg exposure.

Blood, Feather, Egg Hg Content of Wild Loons. A total of 99 adult loons and chicks were captured, banded, and blood collected for Hg analysis in 2002. The following is the range of Hg concentrations in the loon tissues sampled in 2002, expressed as µg Hg/mL whole blood and mg Hg/gm feather-fresh weight.

Development of Hg Exposure Response Curves. We have constructed Hg exposure-response curves relating measure of loon tissue exposure and 3-5 year reproduction history on greater than 100 nesting territories in Wisconsin and the Canadian Maritimes. Productivity is indexed by the number of chicks fledged/territorial pair at lakes which were occupied 3-5 years during the survey period. Data from the Canadian Maritimes were pooled with that from Wisconsin to extend the range of lake pH and loon tissue Hg content. We found negative relationships between loon productivity and the mercury content of prey fish, adult female blood, and egg Hg content at lakes where productivity was quantified.

Negative Effects Greatest in Canadian Maritimes/Acidic Wisconsin Lakes. We found a positive relationship between lake pH and loon productivity, complicating interpretation of the relationship between mercury exposure and productivity. We also will construct mercury exposure-response curves from endpoints derived in laboratory studies. These response curves also will be integrated with the Wisconsin Loon Demographic Model. These experiments are supported with funding from the Electric Power Research Institute, Wisconsin Utilities Association, and Wisconsin Focus on Energy Research Program. With these funds, we conducted dose-response laboratory studies to quantify the level of mercury exposure associated with negative effects on the development of common loon chicks reared in captivity from hatch to 105 days. An additional dose-response experiment will occur in 2003, with funding from the Wisconsin Focus on Energy Research Program, and we will report on impacts of Hg exposure on loon-chick growth, behavior, DNA integrity, immune function, oxidative stress hormones, and histopathology in 2004.

Impact of Stressor Impacts: Habitat Alteration and Human Disturbance

Habitat Alteration (GIS DATA). We used ARCVIEW 3.2 and ARCINFO 8.0.1 to create basemaps and shapefiles containing data collected on our 2002 study lakes. We will evaluate the relationship between shoreline building density and housing density/hectare surface water (indices of human settlement density) with habitat measures.

Human Disturbance. We recorded disturbance rates at 38 loon territories where adult loons were rearing chicks on our study area in 2002. A total of 680 30-minute observations were conducted during the period of June 20-August 31, 2002. Multiple regression analysis will be used to explore the relationship between: (1) rates of disturbance and loon chick survival; and (2) rates of disturbance and indices of anthropogenic impacts including boating activity, shoreline housing density, and the presence/absence of various shoreline developments (public boat landings, campgrounds, marinas, condominiums, etc.).

Loon-Habitat Modeling. 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 development includes a variety of statistical techniques of loon-habitat suitability models to quantify relationships between local characteristics including anthropogenic stressors such as mercury and land use, and the presence and fecundity of loon pairs. The following data were collected at 163 lakes in 2002:

Response Variables: adult loon presence/absence, presence territorial pair, nest success, and chick survival.

Predictor Variables (Lake Parameters): sechi-disk depth, water chemistry, morphometry, boating activity, the presence/absence of boat landings/campgrounds, and disturbance rates.

Predictor Variables (Nest Habitat Parameters): shoreline vegetation type, building locations, nest-habitat quality, the presence/absence of special features (islands, artificial nest platforms, etc.). Nesting habitat was mapped and is being digitized using ARCINFO. Lake morphometry, clarity, and spatial data have been obtained and lake water chemistry will be measured at all lakes in 2003-2004. We also will examine the relationship between nest success and building proximity by determining distance from nest to nearest building, and nest success to building density within 150 m of the nest.

Future Activities:

A loon/Hg dose-response experiment will be conducted in 2003 to establish final Hg effect thresholds for chicks and to validate the loon-exposure model. Field surveys will occur at the same scale and scope as in 2002, and the methods will be similar. Preliminary habitat models will be constructed and modified as additional data are collected in 2003 and 2004. Evaluation of population models and input of demographic data will occur in 2003.

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, 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
  • 2003
  • 2004 Progress Report
  • 2005
  • Final Report