Collapse of a Black Tern Colony (Chlidonias niger) as a Result of Climate Change Driven Lake-Level Extremes and Anthropogenic Habitat Alteration

Related dataset is at https://doi.org/10.7302/d104-mg64 and also listed in the dc.relation field of the full item record.Global climate change is expected to interact with existing environmental stressors and increasingly impact biodiversity. Great Lakes coastal wetlands and wildlife are under multiple threats including development, invasive species, and pollutants. How such stressors interact with climate-change driven, extreme lake level fluctuations to affect wildlife populations is not well understood. We investigate the rapidly declining black tern (Chlidonias niger) populations over a period of eight years in one of Michigan’s largest colonies, at Lake St. Clair. To understand the potential drivers of these declines, we analyzed long-term hatching success data relative to both proximate ecological drivers, as well as large-scale hydrological and geospatial habitat shifts. Landcover and bathymetric data were collected using remote sensing classification and were evaluated regarding their impact on black tern population metrics via stepwise binomial general linear models. Results were then applied to land cover maps to estimate change in habitat characteristics tied to nest vulnerability. Between 2013 and 2020, the colony’s breeding population and nesting success collapsed in tandem with a record rise in lake-levels. Nests with significantly lower hatching success were surrounded by deeper water, more dense, monotypic vegetation, and were located closer to the wave-exposed open area of the main lake. All these characteristics shifted unfavorably with rising lake levels, leading to progressively reduced nesting habitat availability, with a 56% reduction in hatching success and a 77% estimated decline in population size. The zone most favorable to breeding, defined by combination of interspersed native plant communities and floating nest material, was unable to shift upland as lake margins have increasingly become hardened by a combination of anthropogenic development and invasion by Phragmites australis. Subjected to progressively deeper and less stable habitat, nests have failed more frequently, likely due a combination of inclement weather and aquatic predators. Our results demonstrate that the interaction between climate change-driven lake-level rise, invasive species and coastal development are increasingly eliminating safe nesting habitat for black terns. The results also suggest that the resilience of other regional coastal wetlands needs to receive more conservation attendance in the Great Lakes region. We conclude that management must account for multiple stressors to mitigate habitat loss and protect as much wetland reserves as possible so black terns and other marsh birds can adjust to continued hydrologic extremes.Master of ScienceSchool for Environment and SustainabilityUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/167347/1/Fuller_Jennifer_Thesis.pd