Code

CCBTR-21-04

Publication Date

2021

Abstract

Population estimation and overwinter survival of the wintering marsh sparrow guild on the lower Delmarva Peninsula.

The wintering and migratory periods are the most poorly understood intervals of a songbirds’ life, yet they also account for significant mortality. A lack of information about these periods hampers our ability to conserve habitats that support birds and mitigate mortality. In an effort to better understand the factors that influence sharp-tailed sparrow winter ecology, we have established rope-drag sampling transects to reveal what parameters influence abundance, implemented a mark-recapture program to quantify survival, and measured several vegetation characteristics of marshes on the Eastern Shore of Virginia National Wildlife Refuge (ESVNWR) and Fisherman Island National Wildlife Refuge (FINWR). During the winter of 2020-2021, we observed a total of 81 Sharp-tailed Sparrows, 1 Seaside Sparrow, and 1 Marsh Wren during the rope-drag sampling transect surveys. Total birds observed on transects decreased from 36 in period 1, to 24 in Period 2, and 23 in Period 3. The most birds were observed during the first survey period, followed by period 2 and 3, respectively. Of the 83 birds detected, 70 were detected on the initial pass and 13 on the return pass. Detection on days with the mean daily low temperature (39® F) was 0.87 (±0.04). Abundance was relatively consistent among sites in 2021 (mean = 12.59 birds per transect, ±0.13), but was lower and not as consistent among sites during 2013-2014 (mean = 10.00, ±1.83, Figure 4C). Vegetation characteristics were not useful in explaining bird abundance and were not different between control plots and bird observation locations. However, nearly all seeds were disseminated from seed heads by late February. During the three capture periods we accumulated 42 Saltmarsh Sparrow captures, 91 Nelson’s Sparrow captures, 3 Seaside Sparrow captures, and 1 Marsh Wren was captured. Of those captured, 113 were newly banded, 1 bird was a foreign recapture, and 33 birds were within season recaptures. Recapture probability for both Nelson’s and Saltmarsh Sparrows was 0.56 (±0.14). Survival varied between marsh locations and species, but was greater for both species at all locations between the first and second capture periods. For Saltmarsh Sparrows, survival declined from 0.51 (±0.27) between capture period 1 and capture period 2 to 0.12 (±0.09) between capture period 2 and capture period 3 at Bull Marsh, 0.69 (±0.28) to 0.22 (±0.22) at the ESVNWR boat ramp, and 0.90 (±0.14) to 0.53 (±0.31) at FINWR. For Nelson’s Sparrows, survival declined from 0.51 (±0.27) between capture period 1 and capture period 2 to 0.12 (±0.09) between capture period 2 and capture period 3 at Bull Marsh, 0.69 (±0.28) to 0.22 (±0.22) at the ESVNWR boat ramp, and 0.90 (±0.14) to 0.53 (±0.31) at FINWR.

Topic

Abund/Distr, Habitat Quality/Use/Movement, Survival/Mortality, Banding

Species

Nelson's Sharp-tailed Sparrow, Saltmarsh Sparrow, Seaside Sparrow

Source

Center for Conservation Biology Technical Report Series, CCBTR-21-04. William & Mary, Williamsburg, VA.

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