Masters Theses

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

David A. Buehler

Committee Members

David A. Etnier, Sammy L. King

Abstract

The ecological function of freshwater tidal marshes in Atlantic coastal areas may be threatened by increasing salinity resulting from man-made activities such as harbor development, maintenance, and expansion projects associated with shipping channels and ports. Reduced plant diversity has been documented in relation to increasing salinity levels. However, little is known about how increased salinities affect avian communities within tidal marshes along the Atlantic coast. I documented avian communities in tidal marshes of different salinities during the breeding season in 2000 at Savannah National Wildlife Refuge (NWR), Georgia-South Carolina. Study sites included tidal marshes ranging from freshwater to salt marsh conditions, along with forested freshwater and forested intermediate tidal marshes. The primary objective of this study was to identify differences in avian communities correlated with changes in salinity within the tidal marsh system of Savannah NWR. Secondary objectives were to evaluate distributions of king and clapper rail populations across tidal marsh habitats and to evaluate census techniques for these two species.

Seven tidal wetland habitats were selected for study during the summer of 2000. Avian use of these wetland sites was monitored by a series of 10-min, 50-m fixed-radius point counts conducted along transects that systematically covered the study area. Each transect contained two point count stations ≥ 100 m apart and a water monitoring well located in the middle of each transect to sample interstitial salinity. Surveys started 30 min before sunrise and were completed by 10:00 am EDT. Sites were visited twice during the breeding season.

Thirty-four species of birds were documented within the 50-m fixed-radius during point coimts (n=168). Twenty-two other species of birds were documented outside the 50-m fixed-radius. Of these 56 species, twelve species were observed exclusively in the two wooded sites. Seven species were observed only in wooded to freshwater marsh habitats. Seven other species were observed only in wooded to intermediate marsh habitats. Thirteen species were observed across the entire salinity gradient. These species included all of the wading birds, osprey (Pandion haliaetus), boat-tailed grackle (Quiscalus major), red-winged blackbird (Agelaius phoeniceus), and fish crow (Corvus ossifragus). Two species were observed exclusively in brackish to saline marsh conditions and two other species were found only in the salt marsh. Excluding birds that occurred across the salinity gradient, 26 species were observed only in freshwater to intermediate marsh habitats, whereas four species were observed exclusively in brackish to saline marsh habitats. Avian species richness differed (P < 0.0001) across habitats on the study area. Species richness decreased from the freshwater marsh to the subsaline marsh, and then increased slightly in the salt marsh. I detected no apparent relationship between avian abundance and the salinity gradient. The most abundant species censused within the study area were red-winged blackbird, boat-tailed grackle, marsh wren (Cistothorus palustris), and common yellowthroat (Geothlypis trichas).

To evaluate king (Rallus elegans) and clapper (Rallus longirostris crepitans) rail distributions across tidal marsh habitats, tape playback stations were established across the seven sites established for point counts. Tape playback surveys were conducted by boat in the morning from 30 min before sunrise to 9:00 am EDT. I played approximately 12 seconds of the clapper rail's kik-kik-kik call, then followed that with 3 seconds of the king rail's jupe-jupe-jupe call. Birds were counted using standard point count methods. Individual birds that responded to the tape on more than one occasion were circled on the datasheet to ensure no individuals were counted more than once, and visual observations were noted.

Fifty-four rails were observed during point counts (n=168). Three hundred and one rails were documented during playback surveys (n=84). In this study, tape playback surveys were much more effective at documenting rail occurrence than standard point count methods.

Although tape playback is a more effective census technique for documenting king and clapper rail abundance than point counts, call responses of these two species were very similar. Therefore, we recorded their vocalizations with a Sony TC-D5 Pro 11 cassette recorder and a hand held Telinga Pro parabolic (68 cm radius) and Sennheiser microphone. Twenty-two recordings (15 known, 7 unknown) were collected and evaluated using sonogram analysis. Eight clapper rails and seven king rails were visually identified at a range of 5-20 m from the boat before or after their call was recorded.

Discriminant function analysis was used to classify calls of known and unknown rail recordings. Of the eight known clapper rail recordings, the discriminant function analysis assigned all of them to the clapper rail category (100% correct classification); one of the seven known king rail recordings was assigned to the clapper rail category vm (86% correct classification). Six of the seven unknown recordings were assigned to the clapper rail category. Assuming the discriminant function analysis classification was correct, king rails occurred only in the fresh and intermediate marsh habitats. Clapper rails were found throughout the study area with the exception of the freshwater marsh habitats. Thus, king and clapper rail distributions overlapped in the intermediate marsh.

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