Novel method for monitoring common terns at a large colony in northern Lake Huron, USA

Novel monitoring and management techniques may be required when working with colonial waterbirds nesting on anthropogenic sites. We tested the utility of fixed sampling frames (quadrats) for estimating number of common tern (Sterna hirundo) nests and colony dynamics at a site in northern Lake Huron, U.S.A. We also examined whether within-season herbaceous vegetation management affected number of nests. We were unable to detect any avoidance of fixed quadrats (N = 15) versus staked quadrats (N = 15) over 10 count days in 2015 (Mann-Whitney, P ≥ 0.16). Both distance from human disturbance (m) and Julian day were significant (P < 0.01) predictors of number of nests. Based on these findings and using quadrat data from peak count days each year from 2011 to 2016, we estimated a low of 1100 nests in 2013 and a high of 2000 nests in 2016. We also were unable to detect any differences in the number of nests in quadrats with vegetation treatments (N = 10) versus controls (N = 10) during 11 counts in 2016 (Mann-Whitney, P ≥ 0.18). For common terns, and potentially other colonial waterbirds breeding on anthropogenic sites in the Great Lakes, we conclude that a fixed quadrat methodology may provide a useful way of estimating colony size and colony dynamics. Future studies should be conducted to compare our novel method with more traditional monitoring techniques.