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Hanson, E.W. 1996. Monitoring the common loon population in Minnesota: assessment of the 1994 and 1995 survey results, the accuracy of volunteers and aerial surveys, and the power of detecting trends. M.S. Thesis, University of Minnesota. 160 pp.


The common loon (Gavia immer) has been designated as a "Species of Management Concern" by the U.S. Fish and Wildlife Service in Region 3 due to its susceptibility to decline from anthropogenic threats, including habitat loss and degradation, direct human activity (e.g., recreational disturbance, drowning in commercial fish nets), and environmental contaminants (e.g., mercury deposition, acid precipitation, and lead). These threats have likely contributed to the decrease of the breeding range of the common loon over the past century along its southern periphery. Declines in the number of territorial loons and fledging rates have been observed in some regions of Minnesota over the past 10 to 20 years and in the central and eastern Upper Peninsula of Michigan. (See "Literature Review" section at end of preface for more details.) Because of historical declines and current threats, state legislatures and natural resource agencies have listed the common loon as threatened in Michigan, New Hampshire, and Vermont and as a species of concern in Massachusetts and New York.

To determine whether threats are increasing, monitoring programs, usually utilizing volunteers, have been established in most of the northern U.S. and some provinces in Canada by non profit and governmental organizations (e.g., the Maine Audubon Society, Michigan Loon Preservation Society, Minnesota Department of Natural Resources, the Loon Preservation Committee in New Hampshire, Vermont Institute of Natural Science in Vermont, LoonWatch in Wisconsin, and the Canadian Lakes Loon Survey). In 1989, the Minnesota Department of Natural Resources (MN DNR) conducted a statewide survey and found that Minnesota provides over 50% of the loon breeding habitat in the 48 contiguous states. In 1994, the MN DNR initiated the development of a program that could detect changes in the adult loon population and reproductive success more rapidly than would a statewide population estimate and that could provide information about specific causes of a population decline, if a decline were detected.

Before developing a statewide monitoring program, other loon monitoring activities in Minnesota were assessed. Most programs are lake or region specific. The only ongoing statewide program, the Minnesota Loon Survey (MLS), is a collection of data based on repeated surveys over the breeding season from lakes on which volunteers live. Because these data utilize repeated surveys, they may provide useful information on territory occupancy and changes in nesting and fledging success for this specific set of lakes, but many confounding variables likely exist (e.g., bias towards large lakes with homes and lakes with loons). However, conducting repeated surveys on a scale large enough to assess loon activity throughout Minnesota may not be logistically or economically feasible.

In addition to addressing the problems caused by the large number of lakes in Minnesota (approximately 12,000 > 10 acres in surface area), many species specific factors were considered in developing a monitoring program. Because the loon is long lived and can utilize a variety of habitats and food sources, environmental stressors are likely to result in a slow change in adult loon populations. Strong suggested that loon reproductive rates could serve as better indicators of habitat quality (e.g., suitable nesting habitat, adequate food supply, and tolerable levels of human activity). There is much year to year variability in survivorship of juveniles, thus long term data are required to assess trends in productivity. However, the loon's relatively low juvenile survivorship may mean the adult population is the "driving force" in maintaining a demographically stable population. This points to the need to assess both the adult population and productivity.

To know whether anthropogenic threats may be affecting loon populations, changes in adult numbers, territorial pairs, and productivity need to be confirmed first; this is what monitoring programs throughout North America are attempting to accomplish and is the primary goal for the new monitoring program in Minnesota. If populations are changing, especially declining, then there is need to determine the underlying mechanisms of the detected changes.

To address these concerns, the MN DNR and I initiated the Minnesota Loon Monitoring Program (MLMP) in 1994 utilizing volunteers to census over 600 lakes within six regions of the state ("index areas") annually. The objective of the MLMP is to ensure rapid detection of changes in the number of adults and reproductive success in the loon populations within these areas.

Tracking the same set of lakes over time will provide a detailed record of changes in adult and juvenile numbers and densities and number of territories. The design of the MLMP surveys should provide insight into the causes of population and productivity declines, should either be detected. In Chapter 4,1 present the findings from the first two years of this monitoring program.

Because the MLMP is based on complete censuses in six localities, there is no sampling error. However, other sources of error exist in the form of measurement error, which includes observer error, species selection effects (e.g., loon movement), and other environmental effects (e.g., terrain, plot size). It is possible that the census results will be biased if there is substantial measurement error associated with the use of volunteer surveyors. Most loon monitoring programs throughout North America also utilize volunteers to conduct surveys. It is assumed volunteer observations are accurate, yet few studies have attempted to verify this assumption. In chapter 1, several studies are presented that assess the accuracy of volunteer surveys and other sources of variation in loon counts.

I applied the results of the volunteer accuracy studies to an analysis of the statistical power of detecting declines in the MLMP survey regions over time in Chapter 2. If no significant decline is observed after several years of data collection, it would be helpful for the MN DNR to know what rate of change is required and how long monitoring is necessary before a negative trend could be detected. I modeled adult loon population declines with randomized variable counts and statistically assessed the power of being able to detect various decline rates.

I also investigated the accuracy of aerial surveys to count loons in Chapter 3. Many monitoring programs utilize aerial surveys to count loons, including the MLMP. Studies on the accuracy of aerial surveys compared to ground counts have shown considerable variation. In addition, most of these studies have only reported single ratio estimates (sum aerial counts / sum ground counts) without assessing the variability around the ratio.

Each chapter is written to stand on its own, thus some information is repeated. Other chapters in the thesis are referenced as necessary.

The studies assessed in this thesis should provide useful information for the MN DNR and other loon monitoring programs about the use of volunteers, survey methodology, and the population dynamics of the common loon, especially rates of lake use and breeding success. In addition to providing needed information about the status of Minnesota's loons and survey methodology, hopefully this project reaches the lives of the citizens of the state through the volunteers and the stories they share. Because the loon is a species people care about and relate to, generating the support to maintain a healthy loon population and lake habitat is feasible.

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