The Influence of Marsh Size on Marsh Value for Bird Communities of the Lower Chesapeake Bay
Bird abundance and species richness was assessed in 20 salt marshes located on the western shore of the Chesapeake Bay. Marshes were similar in vegetational composition and ranged in size from 0.1 to > 100.0 ha. Over 6,800 observations were made of 105 species. Marsh area was found to be a very good indicator of species richness for all bird groups examined. The slopes of species-area relationships derived were relatively high but similar to those reported from other habitat types. The rate of species loss with decreasing marsh size was highest for those species that use the marsh directly. Patterns of species loss were not random. Bird communities detected in small marshes were completely nested subsets of those observed in larger marshes. The obligate marsh-bird community appears to collapse between 5.0 and 1.0 ha. The frequency distribution of marsh size classes within the study area shows that large marshes are rare. This finding suggests that a fraction of the total marshes support the bulk of the individuals of certain species. However, small marshes do have value for selected species. Bird species detected varied considerably in their use of 15 distinct marsh components. Small tidepools and saltbush supported the greatest number of species and individuals. Over 30% of all individuals detected were observed foraging in tidepools. Other marsh components also contributed to overall species richness.