No abstract

Coastal marshes are one of the world's most productive ecosystems. Consequently, they have been heavily used by humans for centuries, resulting in ecosystem loss. Direct human modifications such as road crossings and ditches and climatic stressors such as sea-level rise and extreme storm events have the potential to further degrade the quantity and quality of marsh along coastlines. We used an 18-year marsh-bird database to generate population trends for 5 avian species (Rallus crepitans, Tringa semipalmata semipalmata, Ammodramus nelsonii subvirgatus, Ammodramus caudacutus, and Ammodramus maritimus) that breed almost exclusively in tidal marshes, and are potentially vulnerable to marsh degradation and loss as a result of anthropogenic change. We generated community and species trends across 3 spatial scales and explored possible drivers of the changes we observed, including marsh ditching, tidal restriction through road crossings, local rates of sea-level rise, and potential for extreme flooding events. The specialist community showed negative trends in tidally restricted marshes (-2.4% annually from 1998 to 2012) but was stable in unrestricted marshes across the same period. At the species level, we found negative population trends in 3 of the 5 specialist species, ranging from -4.2% to 9.0% annually. We suggest that tidal restriction may accelerate degradation of tidal marsh resilience to sea-level rise by limiting sediment supply necessary for marsh accretion, resulting in specialist habitat loss in tidally restricted marshes. Based on our findings, we predict a collapse of the global population of Saltmarsh Sparrows (A. caudacutus) within the next 50 years and suggest that immediate conservation action is needed to prevent extinction of this species. We also suggest mitigation actions to restore sediment supply to coastal marshes to help sustain this ecosystem into the future.

Abstract. Habitat specialists are declining at alarming rates worldwide, driving biodiversity loss of the earth's next mass extinction. Specialist organisms maintain smaller functional niches than their generalist counterparts, and tradeoffs exist between these contrasting life history strategies, creating conservation challenges for specialist taxa. There is little work, however, explicitly quantifying "specialization"; such information is necessary for the development of focused conservation strategies in light of the rapidly changing landscapes of the modern world. In this study, we tested whether habitat specialism explains the persistence of breeding bird populations in tidal marshes of the northeastern United States. We used the North American Breeding Bird Survey (BBS) together with contemporary marsh bird surveys to develop a Marsh Specialization Index (MSI) for 106 bird species that regularly use tidal marshes during the breeding season. We produced four metrics of species persistence (occupancy, abundance, total biomass supported, and 14-yr population trends) and compared them to MSI values in one of the first community-scale demonstrations of specialist loss in disturbed landscapes. Our results confirm that tidal marsh specialism has short-term benefits but long-term consequences for bird persistence in coastal marsh systems, results that are generalizable across many changing landscapes. We then use this robust support of niche theory to recommend MSI as a tool for quantitatively identifying species of conservation concern in disturbed and rapidly changing landscapes such as tidal marsh.

Conserving tidal‐marsh bird communities requires strategies to address continuing pressures from human development to the effects of increasing rates of sea‐level rise. Knowing tidal‐marsh bird distributions and population sizes are important for developing these strategies. In the Northeast United States, where estimates of sea‐level rise are 3 times higher than the global average, 5 bird species are tidal‐marsh specialists: clapper rail (Rallus crepitans), willet (Tringa semipalmata), Nelson's sparrow (Ammospiza nelsoni), saltmarsh sparrow (A. caudacuta), and seaside sparrow (A. maritima). We used a regional marsh bird survey to develop Bayesian network models to identify factors that influence patch‐scale species density and to estimate regional population sizes. We modeled species density as a function of habitat covariates at the patch, local, landscape, and regional spatial scales. Densities were most sensitive to patch location and dimension, patch geomorphic setting, indices of human development, and changes in mean sea level. We estimated 110,000 clapper rails (95% CI = 61,000–159,000), 111,000 willets (95% CI = 70,000–152,000), 7,000 Nelson's sparrows (95% CI = 4,000–10,000), 60,000 saltmarsh sparrows (95% CI = 40,000–80,000), and 234,000 seaside sparrows (95% CI = 112,000–356,000) from the United States–Canada border to, and including, the mouth of the Chesapeake Bay, Virginia, USA. Our abundance estimates can be used to identify priority conservation areas at multiple geographic scales and our models help identify key habitat and landscape components for tidal‐marsh restoration and management to benefit tidal‐marsh birds and can be modified for other species. © 2018 The Wildlife Society.

Salt marsh birds in eastern North America are high conservation priorities due to their restricted ranges, threats from sea-level rise, and an overall lack of information related to their population status or trends. We calculated estimates of detection probabilities for clapper rail (Rallus crepitans), willet (Tringa semipalmata), seaside sparrow (Ammodramus maritimus), and saltmarsh sparrow (A. caudacutus) breeding in Delaware Bay, USA. Our objectives were to model the effects of survey covariates on detection probabilities for occupancy and abundance estimates, determine how survey frequency (no. visits to a site) and survey timing (when in the season sites are sampled) affected the estimates, and how varying the number and timing of visits affected the estimates compared to the recommendations based on the North American Marsh Bird Monitoring Protocol. To make these comparisons, we defined 4 survey frequency (2, 3, 4, and 8 visits) and 3 survey timing (early, early-middle-late, and late season) scenarios. Our results are based on 480 surveys (i.e., call broadcast point counts) to 30 sampling locations located at Bombay and Prime Hook National Wildlife Refuges during the 2008 and 2009 breeding seasons. The scenario of 3 visits early in the season provided the lowest error estimates of occupancy and abundance. Distributing the survey effort across the season, our early-middle-late scenario, provided high variance estimates and should be avoided when designing monitoring programs for these tidal marsh obligate species. Ó 2015 The Wildlife Society.