Leah Ann Culp

Date of Award

5-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

William E. Glanz

Second Committee Member

Thomas P. Hodgman

Third Committee Member

Brian J. Olsen

Abstract

Even seemingly minor habitat modification may have negative consequences for tidal marsh inhabitants like the Saltmarsh Sparrow (Ammodramus caudacutus) and the salt-marsh subspecies of Nelson's Sparrow (A. nelsoni subvirgatus), collectively sharp-tailed sparrows. Roads and bridges that bisect marshes restrict tidal flow and alter natural hydrology. Their removal is currently under consideration by land managers. I investigated sharp-tailed sparrow habitat quality (habitat use by nesting females, nest flooding, and daily nest survival) on state and federal lands in two tidally restricted salt marshes and two unrestricted marshes in Maine. Two restricted areas were behind a single road with a wide bridge >25 m wide. A third restricted area was behind two roads, one with a 3-m wide culvert and a second road downriver with a 25-m wide bridge. On restricted rivers, flood frequency of available high-marsh habitat was reduced by 50% above the two-road restriction compared to areas located below restriction and above just one restriction. Use by nesting sparrows, however, was highest downriver, above one bridge-type restriction. Flood frequency of nests did not differ significantly between restricted and unrestricted areas or between low and high river reaches. Overall nest survival also did not differ between restricted and unrestricted systems, but effect of nest timing on nest survival did vary across restriction types. On low reaches (below restriction), it was important for sparrows to re-nest quickly after failure due to flooding (probability of nest survival decreased by ~35% for every day that clutch completion was delayed past peak high tide). Above tidal restrictions (one-road and two-road restrictions), nest survival was slightly better for nests that were initiated later after peak high tide (survival increased by ~10% for every day of delay). Precipitation increased flood frequency of available high-marsh habitat and was correlated with lower probability of nest survival (although not flood frequency at nests). These results suggest that on the restricted rivers in this study, areas above one bridge-type tidal restriction may be of higher quality to nesting sharp-tailed sparrows than areas located below restriction or the area located above the two-road restriction. The negative effect of precipitation on nest survival suggests sharp-tailed sparrows may be highly vulnerable to global climate change. In addition to rising sea levels, which are predicted to reduce sparrow nesting habitat, climate change is also expected to increase storm intensity and frequency in the Northeast, USA. In the face of changing climate and hydrology, managers should consider carefully before removing tidal restrictions such as those included in this study. Wide bridge-type tidal restriction did not appear to negatively affect high marsh flooding or sharp-tailed sparrow nesting, however wide culvert-type restriction may have had some negative impacts due to reduced flood frequency in the high marsh zone.

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