Nest Survival of Understory Birds in Longleaf Pine Forests Exposed to Fire and Fire-Surrogate Treatments

Abstract

Longleaf pine (Pinus palustris) forest ecosystems evolved with short-interval, low intensity fires. Fire suppression has reduced or eliminated fire and has caused extensive changes in plant community composition and structure. The National Fire and Fire-Surrogate study was implemented to evaluate effects of alternative habitat treatments, such as herbicide application and mechanical thinning, and to compare them with effects of prescribed fire. We evaluated how treatments influenced the nesting success of birds breeding in 10-ha plots of longleaf pine at Solon Dixon Experimental Forest, Alabama. We measured daily rates of nest mortality for 432 nests of 33 species in unmanipulated (controls), burned, herbicide-treated and burned, thinned, and thinned and burned plots during the three years of our study. Although we accumulated observations of 6,624 days that nests were exposed to possible predation, sample sizes were still too small to permit robust statistical analyses of treatment effects. Data from one (Eastern Towhee, Pipilo erythrophthalmus) of two species with the largest sample sizes suggested that nests in treatment plots experienced higher rates of mortality than did nests in control plots, but sample sizes were still small enough that high estimates of variance prevented strong statistical evaluation. Nest survival for the other common species, Northern Cardinal (Cardinalis cardinalis), showed no such suggestive differences. We present results from all nests of all species for which we found three or more nests so that future researchers can use the data during meta-analyses. We also encourage those designing future similar studies to consider expanding the size of study plots so that at least the most numerous open-cup nesting birds can be found in sufficient numbers for strong statistical analyses. In longleaf pine forests of southern Alabama, we estimate that minimum plot sizes would need to be 50 ha for the two most common species, Eastern Towhee and Northern Cardinal.