Population Growth and Demography of Common Loons in the Northern United States

Abstract

We used recent developments in theoretical population ecology to construct basic models of common loon (Gavia immer) demography and population dynamics. We parameterized these models using existing survival estimates and data from long‐term monitoring of loon productivity and abundance. Our models include deterministic, 2‐stage, density‐independent matrix models, yielding population growth‐rate estimates (λ) of 0.99 and 1.01 for intensively studied populations in our Wisconsin, USA, and New Hampshire, USA, study areas, respectively. Perturbation analysis of these models indicated that estimated growth rate is extremely sensitive to adult survival, as expected for this long‐lived species. Also, we examined 20 years of count data for the 2 areas and evaluated support for a set of count‐based models of population growth. We detected no temporal trend in Wisconsin, which would be consistent with fluctuation around an average equilibrium state but could also result from data limitations. For New Hampshire, the model set included varying formulations of density dependence and partitioning of stochasticity that were enabled by the annual sampling resolution. The best model for New Hampshire included density regulation of population growth and, along with the demographic analyses for both areas, provided insight into the possible importance of breeding habitat availability and the abundance of nonbreeding adults. Based on these results, we recommend that conservation organizations include nonbreeder abundance in common loon monitoring efforts and that additional emphasis be placed on identifying and managing human influences on adult loon survival.

Bycatch of wintering common and red-throated loons in gillnets off the USA Atlantic coast, 1996–2007

“…), so 425 000 was used as a best population estimate of common loons that are subject to bycatch in the gillnet fisheries. The age at first breeding is at least 4 yr (Grear et al 2009) but averages 6 yr (Evers 2007), so both values were investigated. Mitro et al (2008) estimated adult survival in northern US populations as 0.92 (95% CI: 0.89-0.95).…”

Spatial gradients of methylmercury for breeding common loons in the Laurentian Great Lakes region

“…Loon studies have also contributed to the scientific community's growing knowledge of Hg pharmacokinetics (Fournier et al 2002;Kenow et al 2003Kenow et al , 2011 and of confounding factors such as prey availability (Merrill et al 2005). Instead of individual-based laboratory studies that were formerly used to extrapolate potential avian effects (Heinz 1979), recent risk assessment efforts with the common loon combine laboratory (Fournier et al 2002;Kenow et al 2003Kenow et al , 2011 and field studies (Burgess et al 2005;Burgess and Meyer 2008;Evers et al 2008) with developing population models (Nacci et al 2005;Evers 2007; Grear et al 2009;Evers et al 2010). This body of knowledge is the basis for the common loon as a principal indicator of MeHg availability for freshwater avian piscivores for (1) developing wildlife criterion values of interest to states (Evers et al 2004) and (2) inclusion within national Hg monitoring programs in Canada (Morrison 2011) and in the United States (Mason et al 2005;Wolfe et al 2007).…”

Common Loon Reproductive Success in Canada: the West is Best but Not for Long

“…Thus, declines in numbers of breeders are not expected until sometime in the future, assuming that there is no adjacent source to offset the losses, e.g., breeders in northern Canada. In addition, declining numbers of breeders are expected to lag behind declining numbers of young because of replenishment from large numbers of nonbreeding young adults (Grear et al 2008), which take 4 to 11 years to secure breeding territories (Evers 2007). The lag could be even longer because of large numbers of young produced about every 10 years (about 1.5 times the long-term mean) under what must be exceptionally good but poorly understood conditions (Evers 2007).…”