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Population Growth and Demography of a Long-lived Piscivorous Bird in Lakes of the Northern United States
Citation:
GREAR, J. S., M. W. Meyer, J. H. Cooley, Jr, A. KUHN, W. H. Piper, M. MITRO, H. S. Vogel, K. M. Taylor, K. P. Kenow, AND D. E. NACCI. Population Growth and Demography of a Long-lived Piscivorous Bird in Lakes of the Northern United States. Presented at The Wildlife Society 15th Annual Conference, Miami, FL, November 08 - 12, 2008.
Impact/Purpose:
This oral presentation contributes to the demonstration and implementation of NHEERL’s Wildlife Research Strategy. That strategy describes methods by which population models will be used to integrate stressor impairments of multiple organismal-level endpoints (e.g., survival and reproduction) into a population-level assessment of ecological risk. Demonstration of this methodology currently focuses on the common loon (Gavia immer) because of the excellent opportunity that species provides to examine the strengths and limitations of the approach. Thus, through collaboration with state and non-government cooperators, this presentation provides a field-parameterized population model that will be used to assess potential risk from multiple stressors such as, for example, mercury contamination and land-use change. The presentation also applies recent innovations in the assessment of observational, process, and model uncertainty, all of which are critical components of probabilistic risk assessment. Such ecological risk assessments provide an important foundation for the development of regulatory limits, so it is anticipated that this research will facilitate their incorporation into the criteria process.
Description:
Common loons (Gavia immer) have captured the attention of evolutionary ecologists and conservation organizations for several decades, leading to a rich supply of observational data on breeding biology, behavior and abundance. Analysis of such data can provide insight into population demography, dynamics, and life history evolution of birds and top predators, but is also critical for identifying and addressing potential impacts of human activity on loon fitness. We use recent developments in theoretical population ecology to construct basic models of loon demography and population dynamics. Parameterization of these models is made possible by bird banding studies and the long-running commitments to monitoring of loon productivity by conservation organizations. Our deterministic, two-stage, density independent matrix models yield population growth rate estimates () of 0.99 and 1.01 for intensively studied populations in Wisconsin and New Hampshire. Perturbation analysis of these models indicates that estimated growth rate is extremely sensitive to adult survival, as expected for this long-lived species. Also, we use annual count data from New Hampshire to examine weights of evidence for a set of count-based models with varying treatments of density dependence and partitioning of stochasticity. Results suggest that annual population growth rate in New Hampshire is indeed limited by density, and therefore possibly by habitat availability.