Comparing functions of natural and created marshes for shorebirds and wading birds

Abstract

Shorebirds and wading birds were observed November 1997 to April 1998 and September 1998 to April 1999 to compare functional values of natural and created marshes on the Texas coast. Study locations included Aransas National Wildlife Refuge (NWR), Nueces Delta Mitigation Project, and Mustang Island, Texas. Analysis focused on black-bellied plover (Pluvialis squatarola), long-billed curlew (Numenitus americanus, peeps (Calidris sandpipers), willet (Cataptrophorus semipalmatus), great blue heron (Ardea herodias), and great egret (Ardea alba). Invertebrate benthos were sampled to determine prey availability. Few significant differences existed in invertebrate density or biomass between sites. No significant differences existed for any variable at Aransas NWR (p>0.05). At Nueces Delta, total biomass (p=0.031) and polychaete biomass (p=0.029) were significantly lower in October 1998 than in February 1998 or 1999, or April 1998 or 1999. Total density (p=0.042) and crustacean density (p=0.049) were significantly higher at the Mustang Island natural site than at the created site. Insect density (p=0.002) and insect biomass (p=0.001) increased significantly from November 1998 to April 1999 on Mustang Island. Cluster analysis showed no overall pattern among avian species' activities by site, location, year, or type of site (natural or created). Mustang Island sites were most similar for black-bellied plover, long- billed curlew, peeps, and willet. Peeps fed in >78% of observations at all sites except Nueces Island 1997-98 (61.3%). Great blue heron and great egret were rarely recorded feeding (<20%) at any site. Patterns of utilization among sites appear species specific, related more to habitat than type of site. Nonmetric multidimensional scaling using the 11 most abundant species separated Mustang Island sites from Nueces Delta sites. Dunlin, peeps, sanderling, willet, snowy egret, and great egret were much more abundant on Mustang Island than Nueces Delta. Availability of tidal flats at Mustang Island probably explains differences in community composition.