Using volunteers to monitor the effects of acid precipitation on Common Loon (Gavia immer) reproduction in Canada: The Canadian Lakes Loon Survey

Abstract

The Common Loon (Gavia immer) is a conspicuous and popular aquatic bird that inhabits large lakes (generally >10 ha) on Precambrian Shield across Canada. Because it relies on fish, it is a key bioindicator species linking acid precipitation to higher trophic levels in aquatic food chains. The Canadian Lakes Loon Survey (CLLS), a monitoring program involving volunteers, was initiated in 1981 to collect information on loon reproductive success, such as the number of loons nesting and the number of young they produce which survive to fledging, to help researchers determine whether loons were adversely affected by acid rain or human disturbance. Between 1987 and 1993, 4236 records for loons nesting on 1529 lakes in Ontario (historically the principal region of study) were received from volunteers. We used logistic regression to examine relationships between loon productivity (number of large young produced per pair for 721 lakes), lake area, and pH (from provincial and federal databases). After controlling for lake size, we determined that loons were less likely to nest on acid lakes (pH<5.5), and when they did attempt to breed, their reproductive success was lower, in part due to the reduced survival of two-chick broods, presumably linked to reduced fish biomass. However, we found no conclusive evidence that breeding success exhibited any temporal trends in relation to pH over this time period. Continued monitoring by volunteers of loon reproduction on CLLS lakes will provide a reliable, costeffective method of assessing the long-term health of large, acid-sensitive lakes across Canada.