Douglas H. Johnson

Although variation in effect sizes and predicted values among studies of similar phenomena is inevitable, such variation far exceeds what might be produced by sampling error alone. One possible explanation for variation among results is differences among researchers in the decisions they make regarding statistical analyses. A growing array of studies has explored this analytical variability in different fields and has found substantial variability among results despite analysts having the same data and research question. Many of these studies have been in the social sciences, but one small “many analyst” study found similar variability in ecology. We expanded the scope of this prior work by implementing a large-scale empirical exploration of the variation in effect sizes and model predictions generated by the analytical decisions of different researchers in ecology and evolutionary biology. We used two unpublished datasets, one from evolutionary ecology (blue tit, Cyanistes caeruleus, to compare sibling number and nestling growth) and one from conservation ecology (Eucalyptus, to compare grass cover and tree seedling recruitment). The project leaders recruited 174 analyst teams, comprising 246 analysts, to investigate the answers to prespecified research questions. Analyses conducted by these teams yielded 141 usable effects (compatible with our meta-analyses and with all necessary information provided) for the blue tit dataset, and 85 usable effects for the Eucalyptus dataset. We found substantial heterogeneity among results for both datasets, although the patterns of variation differed between them. For the blue tit analyses, the average effect was convincingly negative, with less growth for nestlings living with more siblings, but there was near continuous variation in effect size from large negative effects to effects near zero, and even effects crossing the traditional threshold of statistical significance in the opposite direction. In contrast, the average relationship between grass cover and Eucalyptus seedling number was only slightly negative and not convincingly different from zero, and most effects ranged from weakly negative to weakly positive, with about a third of effects crossing the traditional threshold of significance in one direction or the other. However, there were also several striking outliers in the Eucalyptus dataset, with effects far from zero. For both datasets, we found substantial variation in the variable selection and random effects structures among analyses, as well as in the ratings of the analytical methods by peer reviewers, but we found no strong relationship between any of these and deviation from the meta-analytic mean. In other words, analyses with results that were far from the mean were no more or less likely to have dissimilar variable sets, use random effects in their models, or receive poor peer reviews than those analyses that found results that were close to the mean. The existence of substantial variability among analysis outcomes raises important questions about how ecologists and evolutionary biologists should interpret published results, and how they should conduct analyses in the future.

Keys to Field Sparrow (Spizella pusilla) management include providing shrub-dominated edge habitat adjacent to grasslands or grasslands with a shrub component (both of which must include dense grass and moderately high litter cover) and avoiding disturbances that eliminate woody vegetation. Field Sparrows have been reported to use habitats with 16–134 centimeters (cm) vegetation height, 20–145 cm visual obstruction reading, 17–90 percent grass cover, 2–45 percent forb cover, less than 63 percent shrub cover, 3–7 percent bare ground, 14–30 percent litter cover, and 1–7 cm litter depth.

The key to Loggerhead Shrike (Lanius ludovicianus) management is providing open grasslands with scattered trees and shrubs for foraging, nesting, and perching. Loggerhead Shrikes have been reported to use habitats with 20–266 centimeters (cm) vegetation height, greater than or equal to (≥) 10 percent grass cover, 3–48 percent forb cover, 2–25 percent shrub cover, 3–40 percent bare ground, and 11–67 percent litter cover.

Keys to Bobolink (Dolichonyx oryzivorus) management are providing large areas of suitable habitat (for example, native or tame grasslands of moderate vegetative height and density, low shrub density, and moderate litter and forb cover), and protecting nesting habitat from disturbance during the breeding season. Bobolinks have been reported to use habitats with 10–166 centimeters (cm) average vegetation height, 6–75 cm visual obstruction reading, 17–65 percent grass cover, 3–50 percent forb cover, less than or equal to (≤) 22 percent shrub cover, ≤38 percent bare ground, 5–39 percent litter cover, and ≤9 cm litter depth.

First posted April 21, 2023 Director, Northern Prairie Wildlife Research Center U.S. Geological Survey 8711 37th Street Southeast Jamestown, ND 58401 Contact Pubs Warehouse Keys to Dickcissel (Spiza americana) management include providing dense, moderate-to-tall vegetation, particularly with a well-developed forb component, and moderately deep litter. Dickcissels have been reported to use grassland habitats with 4–166 centimeters (cm) average vegetation height, 6–85 cm visual obstruction reading, 11–68 percent grass cover, 1–86 percent forb cover, less than or equal to (≤) 10 percent shrub cover, less than (<) 27 percent bare ground cover, <30 percent litter cover, and ≤ 6 cm litter depth.

First posted January 25, 2023 Director, Northern Prairie Wildlife Research Center U.S. Geological Survey 8711 37th Street Southeast Jamestown, ND 58401 Contact Pubs Warehouse Keys to Clay-colored Sparrow (Spizella pallida) management include providing grasslands with a shrub or forb component or shrub-dominated edge habitat, which includes dense grass and moderately high litter cover, and avoiding disturbances that completely eliminate woody vegetation. Clay-colored Sparrows have been reported to use habitats with 20–186 centimeters (cm) average vegetation height, 3–50 cm visual obstruction reading, 15–74 percent grass cover, 5–23 percent forb cover, less than 30 percent shrub cover, 1–20 percent bare ground, 10–63 percent litter cover, and less than or equal to 5 cm litter depth.

Keys to Burrowing Owl (Athene cunicularia hypugaea) management include providing areas of short, sparse vegetation and maintaining populations of prey species and of burrowing mammals to ensure availability of burrows as nest sites. In particular, the conservation of black-tailed prairie dog (Cynomys ludovicianus) and Richardson’s ground squirrel (Urocitellus richardsonii) colonies is vital to the preservation of Burrowing Owls on the Great Plains. Burrowing Owls have been reported to use habitats with less than 31 centimeters (cm) average vegetation height, 5–12 cm visual obstruction reading, 12–36 percent grass cover, 29–45 percent forb cover, 1–11 percent shrub cover, 11–58 percent bare ground, and 6–27 percent litter cover.

A central challenge in applied ecology is understanding the effect of anthropogenic fatalities on wildlife populations and predicting which populations may be particularly vulnerable and in greatest need of management attention. We used three approaches to investigate the potential effects of fatalities from collisions with wind turbines on 14 raptor species for both current (106 GW) and anticipated future (241 GW) levels of installed wind energy capacity in the United States. Our goals were to identify species at relatively high vs low risk of experiencing population declines from turbine collisions and to also compare results generated from these approaches. Two of the approaches used a calculated turbine‐caused mortality rate to decrement population growth, where population trends were derived either from the North American Breeding Bird Survey or from a matrix model parameterized from literature‐derived demographic values. The third approach was potential biological removal, which estimates the number of fatalities that allow a population to reach and maintain its optimal sustainable population set by management objectives. Different results among the methods reveal substantial gaps in knowledge and uncertainty in both demographic parameters and species‐specific estimates of fatalities from wind turbines. Our results suggest that, of the 14 species studied, those with relatively higher potential of population‐level impacts from wind turbine collisions included barn owl, ferruginous hawk, golden eagle, American kestrel, and red‐tailed hawk. Burrowing owl, Cooper’s hawk, great horned owl, northern harrier, turkey vulture, and osprey had a relatively lower potential for population impacts, and results were not easily interpretable for merlin, prairie falcon, and Swainson’s hawk. Projections of current levels of fatalities to future wind energy scenarios at 241 GW of installed capacity suggest some species could experience population declines because of turbine collisions. Populations of those species may benefit from research to identify tools to prevent or reduce raptor collisions with wind turbines.

The key to Short-eared Owl (Asio flammeus) management is providing large grasslands and wetlands, particularly those that can support high densities of voles (Microtus species). Short-eared Owls have been reported to use habitats with 30–90 centimeters (cm) average vegetation height, 7–47 cm visual obstruction reading, 31–85 percent grass cover, 8–26 percent forb cover, less than 18 percent shrub cover, 43 percent litter cover, and 1–2 cm litter depth.