Effects of direct and indirect habitat alterations on tidal marsh sparrows in the Delaware Bay

Abstract

This research determines how direct (Open Marsh Water Management (OMWM) and parallel grid ditching) and indirect (Mercury (Hg) pollution) marsh alterations affect avian salt marsh obligates: Coastal Plain Swamp Sparrows ( Melospiza georgiana nigrescens) (CPSS), Seaside Sparrows ( Ammodramus maritimus maritimus) (SESP), and Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) (SSTS). Chapter 1 compares nest survival between SESP and CPSS found nesting in two tidal marsh zones, an altered salt marsh and a brackish marsh. SESP, having a closer association with salt marshes, had greater nest survival in a salt marsh compared to a brackish marsh (χ² = 19.56, d.f. = 1, P < 0.01). CPSS, having a closer association with brackish marshes, did not differ in nest survival between the salt and brackish marsh (χ ² = 0.58, d.f .= 1, P = 0.45). Previous habitat alteration from management allowed CPSS to colonize salt marshes, where they proved to be successful. Chapter 2 determines quality of historically altered habitat for breeding SESP by estimating nest survival and nest site vegetation at (1) an old OMWM system, (2) a parallel grid ditched site, and (3) an unaltered marsh for comparison. SESP nest survival did not differ between the OMWM and the reference (χ² = 0.85, d.f. = 1, P = 0.77), or between the parallel grid ditched and the reference marsh (χ ² = 2.88, d.f. = 1, P = 0.09). However, the alterations from OMWM and parallel grid ditching did change natural vegetation communities. Chapter 3 tests the utility of SESP and SSTS as tidal marsh Hg bio-indicator species. I estimated sparrow Hg burdens in five Delaware drainages and found no differences in Hg levels between species (F_1,133 < 0.01, P = 0.99). SESP, which were more abundant, had blood Hg levels highest in two drainages distant from the Delaware Bay compared to levels in one drainage that was close to the Delaware Bay shore (F _4,95 = 2.51, P = 0.05). Seaside Sparrows are the preferred species to use as Hg bio-indicators in tidal marsh ecosystems due to their high abundance and ability to detect differences in Hg levels among drainages.