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Common Tern Conservation

COMMON TERN CONSERVATION        by Jennifer Arnold

We are thankful for your continued support of our work with the Park on common tern (Sterna hirundo) conservation. This has helped us develop and refine management approaches for this species that have greatly improved reproductive success and helped to retain common terns as a breeding species at Presqu’ile. Here, we provide a brief summary of our work at Presqu’ile in 2018.

Summary of management approaches since 2014

Since 2014, development and use of fenced exclosures with overhead wires (coined “predator exclusion grids”) has been implemented. These grids are fenced areas with parallel, visible wires strung ~ 2ft high and ~30 cm apart to allow common terns to land but prevent the ingress of larger species. These grids are carefully constructed over active nests to prevent extensive black-crowned night heron (Nycticorax nycticorax) predation that had been decimating nests with hatching eggs and young chicks in prior years. By 2016, we had expanded our grids to provide over 200 m2 of protected nesting area for common terns on Gull Island. However, due to flooding from extreme high-water conditions in Lake Ontario in summer 2017 these structures were largely destroyed. We responded by developing more flexible versions of these exclosures that could be erected quickly by Park staff and researchers over uneven topography. These appeared to allow moderate productivity from the colony in 2017 regardless of the extremely adverse weather conditions.

Synopsis of 2018 work

Despite the challenges caused by the 100-year flood conditions in 2017, in 2018 we managed to use temporary grids to secure suitable habitat for common terns, allowing them a foothold among a sizeable ring-billed gull colony that had set up close to the management area (as a result of the change in island topography from flooding). In June, once the terns were established, we employed the flexible predator exclusion grids that were quick to erect, robust to erosion, and had been successful in 2017. By July, this gridded area, although smaller than that available in previous years, supported over 90 nests (many recently initiated by immigrating individuals) and 130 healthy chicks (several close to fledging age). Tragically, on July 8th we found all the new nests predated and several large chicks killed, but not eaten, within the exclusion grids. It was clear that black-crowned night herons had somehow manage to enter the grid and were apparently killing tern chicks indiscriminately. This is completely novel behavior: previous research reports that night herons only take what they can eat, mostly hatching eggs or young chicks (Hunter and Morris 1976, Morris et al. 1980, Nisbet et al. 2017).

We responded by partially dismantling the grids to allow the oldest chicks to move away from the colony and by setting up a detection system to capture the nocturnal predation behavior of herons and the responses of the terns. We managed to record behaviors of both predator and prey to help us respond to this unexpected predation threat in the future. However, because most tern parents chose not to leave the area despite continued night heron presence, many chicks remained in the area and were predated by night herons. We observed multiple, individual night herons around the colony, details of predation events, and evidence for how night herons were scaling the grid, that allowed us to develop a new grid design for 2019.

Despite these challenges, in 2018 our activities still facilitated the fledging of approximately 20 chicks from Gull Island. Although not as high as anticipated, this is still considerably better than total colony failure that was commonly observed in the absence of these management approaches.

We are happy that our research and monitoring has allowed us to develop a new grid design and plans for 2019.  Park staff have already laid the groundwork for the construction of this design which will be tested, alongside a slightly modified version of the pre-2017 grid to see which is most successful for attracting birds and maintaining viable chicks. These designs should remove the loop-hole that allowed the night herons to breach our enclosures, improve the overall appeal of the grid to prospecting terns, ease the construction burden and thus protect common tern chicks and eggs against predation.

Other activities of potential interest to Friends in 2018

In addition to research, our student interns also assisted the park with a wide range of activities, from waterbird management on High Bluff Island to environmental education (including Kids ‘n Nature programs and the Nature Center). The generous support of the Friends of Presqu’ile was acknowledged at professional forums in 2018, including the Annual Meeting of the Great Lakes Area Working Group on Colonial Waterbirds and the 27th International Ornithological Congress.

We thank The Friends for their generous support which has helped in our work at Presqu’ile over many years and look forward to continuing our efforts in common tern research and conservation at Presqu’ile in 2019.

Jennifer M. Arnold and Stephen A. Oswald
Division of Science,
Penn State Berks, Reading, PA


Literature cited:

Arnold, J. M., Nisbet, I. C. T. and Oswald, S. A. 2016a. Energetic constraint of non-monotonic mass change during offspring growth: a general hypothesis and application of a new tool. - J. Anim. Ecol. 85: 476–486.

Arnold, J. M. J. M., Tyerman, D. J., Crump, D., Williams, K. L. and Oswald, S. A. S. A. 2016b. Premature feather loss among common tern chicks in Ontario: the return of an enigmatic developmental anomaly. - PeerJ 4: e1959.

Hunter, R. A. and Morris, R. D. 1976. Nocturnal predation by a Black-crowned Night Heron at a Common Tern colony. - Auk 93: 629–633.

LaForest, S. 1993. Birds of Presqu’ile Provincial Park. - Ontario Ministry of Natural Resources.

Morris, R. D., Kirkham, I. R. and Chardine, J. W. 1980. Management of a declining common tern colony. - J. Wildl. Manage. 44: 241–245.

Morris, R. D., Weseloh, D. V, Cuthbert, F. J., Pekarik, C., Wires, L. R. and Harper, L. 2010. Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999. - J. Great Lakes Res. 36: 44–56.

Morris, R. D., Pekarik, C. and Moore, D. J. 2012. Current status and abundance trends of Common Terns breeding at known coastal and inland nesting regions in Canada. - Waterbirds 35: 194–207.

Nisbet, I. C. T., Arnold, J. M. and Oswald, S. A. 2017. Common tern Sterna hirundo. - In: Rodewald, P. G. (ed), The Birds of North America Online. Cornell Laboratory of Ornithology.

Szczys, P., Oswald, S. A. S. A. and Arnold, J. M. J. M. 2017. Conservation implications of long-distance migration routes: Regional metapopulation structure, asymmetrical dispersal, and population declines. - Biol. Conserv. 209: 263–272.

Wilson, S., Bazin, R., Calvert, W., Doyle, T. J. T. J., Earsom, S. D., Oswald, S. A. and Arnold, J. M. 2014. Abundance and trends of colonial waterbirds on the large lakes of southern Manitoba. - Waterbirds 37: 233–244.