New wind-energy facilities and their associated power transmission lines and roads are being constructed at a rapid pace in the Great Plains of North America. Nevertheless, little is known about the possible negative effects these anthropogenic features might have on prairie birds, one of the most threatened groups in North America. We examined radiotelemetry tracking locations of Lesser Prairie-Chickens (Tympanuchus pallidicinctus) and Greater Prairie-Chickens (T. cupido) in two locations in Oklahoma to determine whether these birds avoided or changed movement behavior near power lines and paved highways. We tracked 463 Lesser Prairie-Chickens (15,071 tracking locations) and 216 Greater Prairie-Chickens (5,750 locations) for 7 and 3 years, respectively. Individuals of both species avoided power lines by at least 100 m and Lesser Prairie-Chickens avoided one of the two highways by 100 m. Prairie-chickens crossed power lines less often than expected if birds moved randomly (p < 0.05) but did not appear to perceive highways as a movement barrier (p > 0.05). In addition, home ranges of Lesser Prairie-Chickens overlapped the power line less often than would be expected by chance placement of home ranges; this result was supported by kernel-density estimation of home ranges. It is likely that new power lines (and other tall structures such as wind turbines) will lead to avoidance of previously suitable habitat and will serve as barriers to movement. These two factors will likely increase fragmentation in an already fragmented landscape if wind energy development continues in prairie habitats.

Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassland bird declines in North America due to the adverse effects of fragmentation on breeding bird abundance and reproductive success. To assess the effects of fragmentation on the reproductive success of grassland birds, we measured rates of nest predation and brood parasitism for four species of birds ( Grasshopper Sparrow [Ammodramus savannaru], Henslow's Sparrow[Ammodramus henslowii], Eastern Meadowlark [ Sturnella magna], and Dickcissel [ Spiza Americana] ) in 39 prairie fragments ranging from 24 to>40,000 ha in size in five states in the mid‐continental United States. Throughout the region, nest‐predation rates were significantly influenced by habitat fragmentation. Nest predation was highest in small (<100 ha ) and lowest in large ( >1000 ha ) prairie fragments. Rates of brood parasitism by Brown‐headed Cowbirds (   Molothrus ater ), however, were not consistently related to fragment size and instead were more strongly related to regional cowbird abundance, being significantly higher in regions with high cowbird abundance. Differences in nest‐predation rates between large fragments ( 54–68% of all nests lost to predators ) and small fragments ( 78–84% lost to predators ) suggest that fragmentation of prairie habitats may be contributing to regional declines of grassland birds. Maintaining grassland bird populations, therefore, may require protection and restoration of large prairie areas.

Life‐history studies of prairie grouse have focused on reproductive ecology, habitat use, movement patterns and survivorship, with only cursory or anecdotal references to mortality causes, or they have been of insufficient duration or scale to infer mortality patterns. Because mortality causes and patterns affect other life‐history traits, their determination adds to our overall understanding of grouse demographics. As part of a long‐term study on lesser prairie‐chicken Tympanuchus pallidicinctus natural history in Oklahoma and New Mexico, we recovered 322 carcasses of radio‐tagged birds captured on leks. We were able to determine the cause of death for 260 of these birds. Predation by raptors accounted for the largest number of mortalities (91), followed by collisions with fences (86), predation by mammals (76), collisions with power lines (4), and collisions with automobiles (3). Mortality causes differed considerably between study sites and between sexes, with all collisions more frequent in Oklahoma than in New Mexico, in females than in males, and in older than in young females. Although predation is a major cause of mortality, we argue that predator control may not be effective for grouse conservation. Moreover, in cases where top predators reduce mesopredator population densities, for example those of red foxes Vulpes vulpes, indiscriminate removal of predators may hasten the decline of grouse populations. Land managers striving to conserve prairie‐chickens and other grouse species should attempt to reduce or eliminate collision mortality risks in addition to efforts to improve nesting or brood‐rearing habitat. Collision risks should also be evaluated for potential release sites of translocated or captive‐reared grouse.

Populations of the lesser prairie‐chicken (Tympanuchus pallidicinctus), an endemic grouse of the south‐central United States, have declined precipitously. This species occurs in short‐ and mixed‐grass prairies with sandy soils. Apart from perennial grasses of short stature, prairie‐chicken habitat is characterized by dryland shrubs of the sand shinnery community, particularly the shinnery oak (Quercus havardii) and sand sagebrush (Artemisia filifolia). We measured microhabitat and microclimate characteristics at bird‐centered and random points at the southwestern (New Mexico) and northeastern (Oklahoma) edges of the species' range. We estimated survival by locating radio‐tagged prairie‐chickens (n = 544) from April 1999 to June 2003. We found that lesser prairie‐chickens used sites within the sand shinnery community that had a higher cover and greater density of shrubs (ANOVA: P < 0.0001). Microclimate differed substantially between occupied and random sites (MANOVA: P < 0.0001), and prairie‐chicken survival was higher in microhabitat that was cooler, more humid, and less exposed to the wind. Survivorship was higher for adults that chose microhabitat with a higher cover of shrubs and grasses and a higher density of vegetation. Survivorship was higher for prairie‐chickens that used sites with >20% cover of shrubs than for those choosing 10–20% cover; in turn, survivorship was higher for prairie‐chickens choosing 10–20% cover than for those choosing <10% cover (Cox regression: P < 0.05). Whereas vegetation may recover following moderate habitat disturbance, land managers applying herbicides or otherwise removing shrubs should understand the potentially negative effects of reduced shrub cover on adult survivorship of lesser prairie‐chickens.

2005. Ecological traps in isodars: effects of tallgrass prairie management on bird nest success. Á/ Oikos 111: 159 Á/169.Ecological traps occur when habitat selection and habitat suitability (measured in terms of fitness) are decoupled. We developed a graphical model based on isodar theory to distinguish between an ideal distribution and an ecological trap. We tested the model's predictions using data on breeding bird populations in managed tallgrass prairie in Oklahoma. Between 1992 and 1996 we monitored success for 2600 nests of 26 breeding species in undisturbed, grazed, and burned and grazed plots. We also sampled arthropod biomass and nest predator abundance. Using the isodar model we determined that managed plots are ecological traps: compared with success on plots left undisturbed, nest success on plots that were only grazed was lower, and success on plots that were burned and grazed was substantially lower. Yet birds preferred to nest on managed plots, where arthropod abundance was measurably higher. Reptiles were the most abundant taxon of nest predators, and their abundance was highest in managed plots. Consequently, tree-nesting species had higher nest success than shrub-and ground-nesting birds. Nest success also increased with tree height. We concluded that isodar theory is a useful tool for detecting ecological traps if any component of fitness is measured in addition to animal densities. Our study also suggests that (1) human modification of the environment may alter simultaneously food and predator abundance, (2) the former affects nest site selection and the latter nest success, and (3) such ecosystems are likely to become traps for breeding birds.