A Meta-Analysis of the Effects of Common Management Actions on the Nest Success of North American Birds

Management strategies for the recovery of declining bird populations often must be made without sufficient data to predict the outcome of proposed actions or sufficient time and resources necessary to collect these data. We quantitatively reviewed studies of bird management in Canada and the United States to evaluate the relative efficacy of 4 common management interventions and to determine variables associated with their success. We compared how livestock exclusion, prescribed burning, removal of predators, and removal of cowbirds (Molothrus ater) affect bird nest success and used meta-regression to evaluate the influence of species and study-specific covariates on management outcomes. On average, all 4 management interventions increased nest success. When common species and threatened, endangered, or declining species (as defined by long-term trend data from the North American Breeding Bird Survey) were analyzed together, predator removal was the most effective management option. The difference in mean nest success between treatment and control plots in predator-removal experiments was more than twice that of either livestock exclusion or prescribed burning. However, when we considered management outcomes from only threatened, endangered, or declining species, livestock exclusions resulted in the greatest mean increase in nest success, more than twice that of the 3 other treatments. Our meta-regression results indicated that between-species variation accounted for approximately 86%, 40%, 35%, and 7% of the overall variation in the results of livestock-exclusion, prescribed-burn, predator-removal, and cowbird-removal studies, respectively. However, the covariates we tested explained significant variation only in outcomes among prescribed-burn studies. The difference in nest success between burned and unburned plots displayed a significant, positive trend in association with time since fire and was significantly larger in grasslands than in woodlands. Our results highlight the importance of comparative studies on management effects in developing efficient and effective conservation strategies.