Code
CCBTR-23-10
Publication Date
2023
Abstract
The tidal saltmarsh habitat in the Chesapeake Bay region supports a diverse marsh sparrow suite during winter. Research on the status and distribution of these species has primarily focused on the breeding season despite the fact that winter accounts for a significant portion of songbird mortality. A lack of information about this period hampers our ability to conserve habitats that support birds. To better understand the factors that influence marsh sparrow winter ecology, we used capture-recapture sampling and double-pass rope drag transect surveys to explore parameters that affect winter mortality and density on the Eastern Shore of Virginia National Wildlife Refuge (ESVNWR) and Fisherman Island National Wildlife Refuge (FINWR). During the winter of 2020-2023, we captured 124 Nelson’s sparrows, 74 saltmarsh sparrows, and 24 seaside sparrows. Our top Cormack-Jolly-Seber model included a time-varying predictor that accounted for differential survival between the early and late portions of the winter, bird species, marsh identity, and an interaction between marsh and species within the survival function of the model with zero predictors in the recapture function. Recapture probability was estimated at 0.34 ± 0.07 SE. and daily survival ranged from 0.97-1.00, depending on species, study site, and winter period (early/late). Survival was higher during the early portion of winter for all species, possibly because seed availability declines throughout the winter. Survival was similar among all study sites for saltmarsh sparrows, highest for Nelson’s sparrows at the ESVNWR boat ramp marsh and highest for seaside sparrows at FINWR. We observed 226 sharp-tailed sparrows and 12 seaside sparrows on double-pass rope drag transects. We were unable to incorporate seaside sparrows into N-mixture models due to data deficiency. For saltmarsh and Nelson’s sparrows, survey site, survey season and an interaction between the two terms were included within the abundance function of our top model. Transect identity was included within the availability function of our top model and no predictors were included in the detection function. Detection was estimated at 0.86 ± 0.03 SE. Saltmarsh sparrow densities were between 0.6 – 1.3 birds per ha and were highest at a transect in ESVNWR Bull Marsh while Nelson’s sparrow densities were between 0.6 – 3.2 birds per ha and were highest at ESVNWR Boat Ramp Marsh. Saltmarsh and seaside sparrows were both associated with marshes with more cover and seed availability though saltmarsh sparrow densities were greatest in portions of the marsh further from the upland-marsh transition zone while seaside sparrows observations and survival were positively associated with marshes with taller vegetation like that found near the margins of tidal waterways. Nelson’s sparrows were associated with marsh that lacked attributes favored by saltmarsh and seaside sparrows, possibly to avoid interspecific competition. Some evidence for intra-specific habitat segregation also exists for Nelson’s sparrow as sex ratios skewed female at ESVNWR Boat Ramp Marsh and male at other field sites. The other two species of marsh sparrows had relatively even sex ratios at all sites.
Topic
Abund/Distr, Habitat Quality/Use/Movement
Species
Nelson's Sharp-tailed Sparrow, Saltmarsh Sparrow, Seaside Sparrow
Source
Center for Conservation Biology Technical Report Series, CCBTR-23-10
Recommended Citation
Hines, C. H., L. S. Duval, and B. D. Watts. 2023. Winter Abundance and Survival of Sharp-tailed Sparrows at the Eastern Shore of Virginia NWR: Final Report. Center for Conservation Biology Technical Report Series: CCBTR-23-10. William & Mary, Williamsburg, VA. 29 pp.
