One of the original goals of the Ontario Lakes Loon Survey (OLLS, now the Canadian Lakes Loon Survey) was to collect reproductive data on Common Loons that would help researchers determine whether loons were adversely affected by acid rain. The Canadian Wildlife Service, Ontario Region (CWS) Long Range Transport of Airborne Pollutants (LRTAP) program has been actively involved in the Ontario portion of the CLLS since its inception, providing both financial support to the survey since 1981 and contributing survey data on loon reproduction for lakes situated near Sudbury and Sault Ste. Marie since 1987. CWS analysis of the 1987 and 1988 Ontario volunteer data suggested that there was indeed a negative impact of lake acidification on Common Loons, although this was based on relatively few lakes, particularly acidic ones (Wayland and McNicol 1990). Given these findings, the CWS and LPBO embarked on a joint, detailed study of the effectiveness of the Survey and the implications Survey data demonstrated for loons breeding in Ontario, particularly in relation to the acid rain problem.
Between 1987 and 1990, LPBO received 2349 records on 1176 lakes across Ontario as part of the OLLS. For our analyses, we wanted to use only data that were collected on entire lakes, and data for all of the pairs on these lakes. Based on the 1987/1988 analyses, we included data from completely surveyed lakes smaller than 500 ha (846 lakes). Of these, 663 contained sufficient data to classify the reproductive success of each pair of loons on a lake into one of the following four categories: 1) lakes with no territorial pairs (no attempts), 2) lakes with territorial pairs but no large young (unsuccessful), 3) lakes where less than one large young was produced per territorial pair (low production), and 4) lakes where more than one large young were produced per territorial pair (high production). pH data were available for only 585 of these lakes; chick survival was determined on 260 of the 585 lakes. (Note: one of the goals of the CLLS water sampling program is to gather or update pH data on many of these lakes so much of the old and future loon data can be analysed with respect to lake chemistry. Clearly our ability to measure and interpret effects regionally will improve as our knowledge of the lake chemistries is expanded).
The 1987-1990 data indicated that the most important factor influencing loon reproductive success was the size of the nesting lake. Loons were more likely to be found on large lakes than small lakes, and had higher breeding success on large lakes. This finding is consistent with results found elsewhere in North America, and may be related to the amount of fish produced in small versus large lakes. One study in Nova Scotia suggested that loon pairs need approximately 40 ha to provide enough fish to successfully raise chicks (Kerekes 1990).
In addition to the effect of lake area, we found that territorial pairs tended to avoid acid lakes as breeding sites, and when they did use them, they tended to be less successful on lower pH lakes. However, these results were not statistically significant. Territorial pairs bred successfully (i.e. produced at least one large young) on 61, 69 and 73% of lakes with pH <6.0, 6.0-7.0, and >7.0 respectively. Within these pH categories, territorial pairs produced on average 0.69, 0.80 and 0.86 large young per pair. We suspect that we would have found an even greater difference in reproductive success across lakes varying in pH if more data were available for quite acidic lakes. In this study, only 2% of the lakes had pH values of less than 5.0 (very acidic lakes), whereas 84% were above pH 6.0 (usually well-buffered lakes where little damage from acid rain is thought to occur). Indeed, preliminary analysis of data collected since 1990 indicates a strong effect of pH on reproductive success below the pH 6.0 threshold used in the present analysis, in agreement with the findings of Alvo et al. (1988) for lakes in the Sudbury area.
While there was only a trend of lower reproductive success for loons breeding on somewhat acidic lakes, survival of two-chick broods was 9% lower on these lakes, a significant difference. We suspect that loon parents may have difficulty finding enough food to successfully rear two chicks on acid-stressed lakes. It is well-known that the availability and diversity of many of the important prey species for loons (e.g. fish, crayfish) are reduced on lakes below pH 6.0. When loons hatch two chicks on these lakes, the larger sibling may dominate the parents' attention and obtain most of the food captured for the young. We also suspect that parents may lay only one egg when they breed on acid-stressed lakes — this is certainly the pattern observed on CWS study lakes near Sudbury.
The combined findings that loons avoid breeding on acid lakes, that when they do they tend to have lower breeding success, and that two chick broods fare poorly on these lakes provide strong evidence that lake acidity has a negative influence on Common Loon reproductive success in Ontario. Despite this, the overall average production of 0.8 large young per territorial pair found in this study is relatively high (McIntyre 1988), and suggests that in Ontario local populations of loons may have been negatively affected by lake acidification, but the province-wide population has probably experienced few effects. Nonetheless, we point out three important considerations demonstrated from this research: 1) that it is very important for volunteers to get the most complete information possible on their lakes, even if loons are not present, so their data can be included in future analyses, 2) that data collected by Survey volunteers provide valuable scientific information that cannot be collected by any other cost-effective means, and 3) because loons are an effective biomonitor of lake acidification, long- term monitoring is critical to determine whether the situation with loons is improving, and hence whether the situation with other wildlife is expected to improve.
Efforts are currently underway to curb the emissions of acid-causing pollutants in both Canada and the United States. The CLLS plays an integral role in Canada's efforts to monitor the effectiveness of these emission controls and determine whether the capability of our lakes and rivers to support healthy wildlife and fisheries resources is improving as water quality improves. By assisting as volunteers, you provide the main link between the conditions in our wilderness and our ability to interpret and respond to changes over time. We thank everyone for their efforts to date, and we hope you will continue to contribute to the CLLS in any way possible.
References
Alvo, R. A., D. J. T. Hussell, and M. Berrill. 1988. The breeding success of common loons in relation to alkalinity and other lake characteristics in Ontario. Can. J. Zool. 66: 746-752.
Kerekes, J. J. 1990. Possible correlation of summer Common Loon (Gavia immer) population with the trophic status of a waterbody. Verh. Internat. Verein. Limnol. 24: 349-353.
McIntyre, J. W. 1988. The Common Loon: spirit of northern lakes. University of Minnesota Press, Minneapolis.
Wayland, M., and D. K. McNicol. 1990. Status report on the effects of acid
precipitation on common loon reproduction in Ontario: the Ontario Lakes Loon Survey. CWS
Tech. Rep. Ser. No. 92.
- Don McNicol and Mark Mallory
Canadian Lakes Loon Survey Bird Studies Canada
P.O. Box 160, Port Rowan,
Ontario, Canada N0E 1M0
Tel: 519-586-3531 Fax: 519-586-3532
Questions about the CLLS? Please contact Kathy Jones
Email: aqsurvey@bsc-eoc.org