James E. Panaccione, M.S. student
Natural Resources: Wildlife

Research Title: Invasive Shrubs and Early-successional Bird Communities: Are Exotic Shrubs a Limiting Factor on Local Populations?

Advisor: Dr. John A. Litvaitis

Description of Research

More than 2,000 species of alien plants are established within the continental United States (Vitousek et al. 1997).  In the Northeast, disturbance-generated habitats (including native shrublands and early-successional forests) are especially vulnerable to alien plant invasion.  Regionally, these habitats support a diverse assemblage of plants and animals, including several obligate songbirds.  However, the northeastern Breeding Bird surveys have indicated a significant decline for nine species associated with early-successional habitats.  Loss of habitat may be a key factor affecting the populations of these shrubland obligates, but the invasion of exotic shrubs may be compounding the issue.

Several studies have suggested that invasive vegetation reduces phytophagous insect abundance.   As a result, species dependent on insects as a food resource, including nesting songbirds, may be less abundant, and have reduced fecundity, in highly invaded habitats.  Recently, a study in the western United States (Ortega et al. 2006) found that sites dominated by the exotic forb spotted knapweed (Centaurea malculosa), had reduced densities, site fidelity, and reproductive success, of chipping sparrows (Spizella passerina).  However, there are very few studies that have examined the effects of non-native vegetation on taxa at higher trophic levels, so we will begin to investigate this relationship in the Northeast by monitoring early-successional avifauna.

My overall research goal is to determine if early-successional bird communities are affected by an abundance of invasive shrubs.  The specific objectives of my research are:

1. Determine if invasive shrubs reduce the overall abundance and species richness of early-successional avifauna.

2. Examine if seasonal fecundity of insectivorous songbirds is reduced at sites with a high percentage of invasive shrubs.

3. Determine if territory size of insectivorous songbirds is influenced by invasive shrub coverage.

To assess abundance and species richness 50-meter fixed radius point counts will be conducted three times, per site, throughout the breeding season.  Nest searching and monitoring will be conducted to examine seasonal fecundity; and spot mapping of target species will be used to determine differences in territory size.  My study sites are “old-field” shrublands located in Strafford and Rockingham counties of southeastern New Hampshire.