Predation of artificial nests in grassland/shrubland habitats in western Tennessee

Grassland and early successional plant communities formerly comprised important components of the southeastern landscape. Many early successional communities have disappeared in the absence of maintenance mechanisms to preserve their existence in the landscape. Today, avian species of grassland and early successional communities are experiencing dramatic declines throughout their range (Askins 1993). Declines in the southeastern United States may be largely related to habitat loss. I focused on two habitats representative of grassland/shrubland successional stages that currently exist throughout the Southeast, old fields and open woodlands. Eight study plots of approximately 1.89 ha each were selected, 4 in each habitat type, on Ames Plantation near Grand Junction, TN. Avian communities were censused on the study plots to identify species presence and relative abundance. Artificial nests were used to gather information on relative predation trends within the old-field and open-woodland habitats. Four study plots were randomly selected as experimental plots (2 field and 2 forest plots) on which rodent populations were reduced to determine the effects of rodents on artificial nest success. Avian communities mostly consisted of mixed-habitat species, capable of inhabiting several different habitat types (red-winged blackbird, Agelaius phoeniceus,indigo bunting, Passerina cyanea, and eastern towhee, Pipilo erythrophthalmus). Several species characterized as early successional habitat specialists (yellow-breasted chat, Icteria virens, northern bobwhite, Colinus virginianus, and field sparrow, Spizella pusilla) were present on the study area. Grassland specialists were rare (one nesting pair of easternmeadowlark, Stumella magna, in two years) despite available habitat and may result from the high area-sensitivity of most grassland birds in conjunction with the relatively small size of available habitat patches on the study area. Kill-trapping of rodents decreased rodent populations below pre-treatment levels on experimental plots (P = 0.001). Trapped areas experienced lower artificial nest predation by rodents and greater nest success than untrapped plots (nests containing fincheggs, P = 0.002, nests containing bobwhite eggs, P = 0.001). Predation by non-rodents remained relatively stable between treatments, despite rodent removal. Therefore, there appeared to be no compensatory response to rodent removal in terms of increased predation on artificial nests by non-rodents. Rodents were responsible for the majority of predation, predating more nests than all other sources combined (64.8% of all nests predated). The most abundant rodents on the study area were the white-footed mouse {Peromyscus leucopus) and the hispid cotton rat (Sigmodon hispidus). Predation of artificial nests by medium-sized mammals (striped skunk. Mephitis mephitis, opossum, Didelphis virginiana, and raccoon, Procyon lotor) was infrequent, accounting for approximately 7.0% of all predation. Predation on nests containing finch eggs occurred with greater frequency than predation on nests containing bobwhite eggs (P = 0.001). Because rodents were the predominate nest predators, this result supports the hypothesis that small-mouthed predators may be less capable of biting into larger eggs such as northern bobwhite (Reistma et al. 1990, Roper 1992, Haskell \995a,b). The use of large eggs such as northern bobwhite in artificial nest experiments may reduce the likelihood of predation by small rodents. Predation rates differed with habitat type, as forested plots experienced much greater predation than field plots (P= 0.001). Nests placed within dense vegetation were less likely to be predated than nests placed in sparser vegetation (P = 0.006). Nests placed in grass were less likely to be predated than nests placed in woody vegetation (P = 0.012) or forbs (P = 0.022). Land managers may succeed in sustaining populations of early successional nesting birds by addressing nesting requirements with habitat manipulations. Habitat improvements that increase quality and composition of nesting cover may reduce predation rates. Future research needs include development of management strategies that benefit the variety of avian species using grassland and early successional habitats