Conservation ecology of tidal marsh sparrows in New Jersey
Date
2015
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Publisher
University of Delaware
Abstract
From 2011 - 2013, I studied breeding populations of Saltmarsh (Ammodramus caudacutus ) and Seaside (A. maritimus ) sparrows on Edwin B. Forsythe National Wildlife Refuge, New Jersey, to inform conservation and management efforts. I compared nesting ecology and reproductive success of these endemic tidal marsh birds, evaluated the role of a nest flooding vs. nest predation tradeoff in shaping nest-site selection, described tidal marsh resiliency to a stochastic disturbance, and quantified the ability of management actions to improve sparrow population viability given sea-level rise impacts. Using data from 465 sparrow nests, I estimated nest flooding and nest predation probabilities using Markov chain models, and quantified a nest-site niche for each species as a 7-dimensional hypervolume. Counter to predictions, Seaside Sparrows had a 3.5 times lower nest flooding probability and a 1.6 times lower nest predation probability than Saltmarsh Sparrows, as well as a 66% larger nest-site niche. A flooding vs. predation tradeoff does not appear to be the primary influence on nest-site niche. Instead, time since marsh colonization may play a larger role, as the ancestral species, Seaside Sparrows, occupied a larger nest-site niche and had higher overall nest success. Stochastic disturbances, such as storms, affect tidal marsh habitats and endemic species, but factors influencing species' responses are not well-understood. Hurricane Sandy made landfall on October 29, 2012 in New Jersey and had devastating impacts on human-dominated landscapes. Using pre- and post-storm measurements, I evaluated the short-term resilience, defined as a resistance to change or a rapid return to pre-storm conditions, of vegetation cover/composition, meadow vole ( Microtus pennsylvanicus ) abundance, and Saltmarsh and Seaside sparrow abundance and reproductive success. By comparing measurements taken three to six months pre-storm with seven to 11 months post-storm, I found a high degree of resilience to Hurricane Sandy. Vegetation cover/composition and sparrow abundance and nest success remained largely similar between 2012 and 2013. Although meadow vole abundance was 1.5 - 19.2 times lower following the hurricane, I detected a rapid increase from June to July 2013, indicating resiliency in the population. Vole recolonization of the marsh may have been facilitated by proximity to upland refugia. Sea-level rise (SLR) poses the most severe and immediate threat to endemic tidal marsh birds in North America. To inform managers of the relative benefit of management actions for tidal marsh birds given SLR impacts, I conducted a population viability analysis of Seaside Sparrows. I quantified the upper (0.75 m of SLR) and lower (0.35 m of SLR) bounds of probable SLR effects on Seaside Sparrows over 42 years, and compared the relative benefit of improving nest success and reducing habitat loss given SLR impacts. A total population decline of up to 70% was highly likely (mean likelihood = 0.96) under 0.75 m SLR, and improving nest success had a greater benefit than reducing habitat loss. Improving nest success under 0.75 m SLR resulted in a population decline that was equivalent to the decline predicted by 0.35 m SLR. To maintain viable populations of tidal marsh breeding birds over the short-term, management actions should focus on increasing nest success via predator exclusion or flood mitigation.