Aquatic Birds
Warmer air temperatures, variable precipitation patterns, and changes in vegetation will very likely reduce the abundance and diversity of aquatic bird species, including the iconic common loon. Earlier snowmelt means changes in seasonal duration and timing, which greatly impacts life cycles, including growth and survival rates of loons and other bird species. Monitoring these populations will help assess the effects of climate change on native species in the watershed.
In 2020, Loon Conservation Associates (LCA) continued a collaborative study with KLWA to conduct comprehensive common loon monitoring surveys in the Kezar Lake watershed. More than fifteen volunteers helped conduct over 450 independent surveys of seven waterbodies in 2020. Out of sixteen documented territorial pairs, ten pairs nested and four nests were considered successful. Two adult loons were captured and banded on Kezar Lake using traditional night-lighting techniques. Four of seven total chicks survived to fledge (defined as more than six weeks of age). Overall productivity in the Kezar Lake watershed in 2020 was 0.25 fledged young per territorial pair. Two pairs used rafts to nest, and each nest successfully hatched a chick. The rate of success was 33% for raft nesting loons compared to 14% for natural nests. These metrics mark the lowest productivity recorded in the first three years of this study and are below the 0.48 productivity threshold needed to sustain a healthy loon population. However, interannual variability in loon productivity is common, and one year does not reflect long-term trends. Low productivity in 2020 is linked to reduced nesting frequency and nest failure. Six of the seven lakes with suitable nesting habitat were occupied by loon pairs, which suggests a healthy breeding population. High levels of mercury (Hg) were measured in blood samples of an adult in the upper bay.
Overall, the adult loon population at Kezar Lake has been constant with some annual changes in the last 36 years (Fig. 1). No statistically significant trend (based on Mann Kendall Trend Test) was found for either adults or chicks over the observation period.
Fig. 1 Annual loon counts for adult and chick populations observed at Kezar Lake from 1983-2021.
The ponds have a much sparser data set:
Based on 17 non-consecutive years of observations, Horseshoe Pond hosts an annual chick population varying from zero to three, and Farrington Pond hosts a few adult loons with only two chicks seen in 2016. One nesting pair was documented on Horseshoe Pond in 2020 with one successful chick fledging. One territorial pair was documented on Farrington Pond in 2020 but nest failure was observed.
Based on 21 non-consecutive years of observations, Heald Pond hosts an annual adult population varying from zero to three. The first chick was documented in 2015. One nesting pair was documented on Heald Pond in 2020, and one of two chicks survived to fledge.
Based on 32 years of non-consecutive observations, Cushman Pond hosts an annual adult population varying from zero to three. The first and only two chicks were documented in 2011. One territorial pair was documented on Cushman Pond in 2019, and nest failure for unknown reasons was documented.
Based on 13 non-consecutive years of observations, Trout Pond hosts an annual adult population varying from zero to two. The first two chicks were documented in 2017. No nesting pairs were documented on Trout Pond in 2020 but a territorial pair were observed.
Surveys were completed on Bradley Pond in 2020 but no loons were found.
Estimation of loon population in southern Maine conducted by the Maine Audubon shows an increase in loon population despite climate change impacts. The study suggests that if lakes are clear, the food supply is abundant, and any adverse human impacts are avoided, the loon population will likely remain stable and/or increase.