Possible Impact of Multiflora Rose on Breeding-Bird Diversity in Riparian Forest Fragments of Central Delaware

Abstract

The populations of many North American forest-breeding songbirds have declined over the past few decades, initiating much research regarding the factors influencing avian use of remaining forests, many of which are highly disturbed and impacted by invasive plants. Our objective was to compare the species richness of breeding birds in riparian forest fragments that contain different amounts of the invasive shrub, Rosa multiflora (Multiflora Rose). We conducted 20 point counts in each of three sites from early June until mid-July of 2008 and 2009, and estimated species richness and relative richness using the program COMDYN4. During 2008, species richness was lower at the site with the most Multiflora Rose. However, the number of species at that site increased by 33% from 2008 to 2009, whereas the number of species in the other two sites remained similar. Consequently, we did not detect differences in species richness among sites during 2009. Despite the increase in species richness at the more heavily invaded site, several common ground- to shrub-nesting species did not occur at that site during either year. Multiflora Rose may reduce the species richness of breeding birds in forest fragments, but additional research coinciding with the control and removal of this invasive shrub will be needed to infer such a relationship.