Factors influencing productivity of common loons (Gavia immer) breeding on circumneutral lakes in Nova Scotia, Canada

Abstract

Common loons (Gavia immer) are top predators that are sensitive to biotic and abiotic conditions associated with their breeding lakes, so factors such as lake chemistry and human activity or disturbance are thought to influence their seasonal and long-term reproductive success. We used two indices of loon productivity to evaluate (1) temporal patterns and (2) relationships with physical and chemical lake characteristics and human activities. Data collected from 1991 to 2000 by volunteers of the Canadian Lakes Loon Survey (CLLS) in Nova Scotia showed that loon productivity, as indexed by both the proportion of resident pairs that produced at least one large young (P s1) and the proportion of successful pairs that produced two large young (P s2), did not vary substantially from year to year and showed no linear trend from 1991 to 2000. Average estimates (1991– 2000) for P s1 and P s2 were 0.49±0.02 and 0.43±0.03, respectively, and the mean number of chicks per residential pair over that time was 0.75±0.04. We found that human disturbance and shoreline development did not influence loon productivity during the prefledging stage on lakes surveyed by CLLS volunteers. Proportion of resident pairs rearing at least one large young was independent of dissolved organic carbon (DOC) concentrations of breeding lakes, but there was a positive relationship between the proportion of successful pairs rearing two large young and DOC. Both indices of loon productivity tended to be negatively correlated with lake pH. These results were not consistent with other findings that loon productivity generally declines with lake acidity, but likely reflect the preponderance of circumneutral (pH 6.5– 7.0) lakes surveyed by the CLLS volunteers in Nova Scotia.