David M. Leslie

Invertebrate Community Response to a Shifting Mosaic of Habitat

Abstract Grazing management has focused largely on promoting vegetation homogeneity through uniform distribution of grazing to minimize area in a pasture that is either heavily disturbed or undisturbed. An alternative management model that couples grazing and fire (i.e., patch burning) to promote heterogeneity argues that grazing and fire interact through a series of positive and negative feedbacks to cause a shifting mosaic of vegetation composition and structure across the landscape. We compared patch burning with traditional homogeneity-based management in tallgrass prairie to determine the influence of the two treatments on the aboveground invertebrate community. Patch burning resulted in a temporal flush of invertebrate biomass in patches transitional between unburned and patches burned in the current year. Total invertebrate mass was about 50% greater in these transitional patches within patch-burned pastures as compared to pastures under traditional, homogeneity-based management. Moreover, the mosaic of patches in patch-burned pastures contained a wider range of invertebrate biomass and greater abundance of some invertebrate orders than did the traditionally managed pastures. Patch burning provides habitat that meets requirements for a broad range of invertebrate species, suggesting the potential for patch burning to benefit other native animal assemblages in the food chain.

Facts From Feces: Nitrogen Still Measures Up as a Nutritional Index for Mammalian Herbivores

Abstract Fecal nitrogen (FN) has been applied widely as an index of dietary quality in studies of nutritional ecology of free-ranging and captive vertebrate herbivores, particularly ruminants. Three related articles in the Journal of Wildlife Management (JWM; Leslie and Starkey 1985, 1987; Hobbs 1987) have been cited (n = 150) in 87 publications and 39 peer-reviewed journals. The critique by Hobbs (1987) and the reply by Leslie and Starkey (1987) on limitations and appropriate applications of FN have been used to justify use of FN or negate its value as a nutritional proxy. We undertook a retrospective analysis of FN applications since 1985, largely because we sensed that methodological cautions noted in the 3 JWM publications were not being followed, leading to faulty conclusions and management applications, and that application protocols needed updating. From January 1986 through July 2007, the 107 species-by-continent applications of FN, citing the 3 JWM publications singly or in any combination, were diverse; FN was used in various ways on 5 continents and for 50 wild and domestic species. Cumulative rates of departure from recommended FN applications increased in recent years, largely in studies that compare different species while failing to fully acknowledge that differences likely reflected digestive capabilities rather than differences in some aspect of dietary intake. Post-1985 research on plant secondary compounds (e.g., tannins) has refined limitations to the application of FN, permitting more straightforward protocols than were possible in 1985. Although use does not necessarily reflect value, the number of published applications during the past 22 years indicates that peer reviewers from a variety of scientific disciplines view FN as a suitable proxy for nutritional status, which can be used to contrast study units when carefully defined by the study design. Any index can have shortcomings, and there are still circumstances when application of FN is problematic. Precise prediction of intake with FN under field conditions is still hampered by inherent variability, but contrasts of comparable study units and species can be appropriate. Published protocols for FN, as amended herein, should be adhered to, and conclusions are strengthened by the use of multiple nutritional indices.

Influence of Landscape Composition and Change on Lesser Prairie-chicken (Tympanuchus pallidicinctus) Populations

Abstract Home ranges of lesser prairie-chickens (Tympanuchus pallidicinctus) include up to several thousand ha of several habitat types that are concentrated around leks (traditional display grounds). A geographic information system (GIS) was used to relate changes in vegetation and land use to population trends of lesser prairie-chickens in Oklahoma, Texas and New Mexico. We quantified changes in vegetation within 4.8 km of lesser prairie-chicken leks and examined relationships among those changes and long-term population trends based on the number of displaying males per lek. Five of 13 populations declined between 1959 and 1996. Landscapes in which populations of lesser prairie-chickens declined were characterized by greater rates of landscape change and greater loss of shrubland cover types than landscapes in which populations did not decline. Changes of specific cover types were not as important as the total amount of change occurring on landscapes. Conservation of lesser prairie-chickens should focus on stability of vegetation and land use and specifically attempt to maintain continuity of shrublands within 4.8 km of existing leks.

Dynamics of a recolonizing population of black bears in the Ouachita Mountains of Oklahoma

Abstract Understanding how populations expand to recolonize former habitats is important to restoration efforts in wildlife management and conservation. Translocation of black bears (Ursus americanus) to Arkansas in the 1950s and 1960s has led to recolonization of former bear range in Oklahoma, with substantial increases in distribution and abundance of the species in Oklahoma over the last 15 years. We studied demographics of black bears in southeastern Oklahoma from May 2001 to November 2002 to provide insight into characteristics of recolonizing populations of large carnivores. We trapped 51 black bears (22 M, 29 F) 77 times and radiocollared 25 female bears. Sex ratios of adults and cubs were skewed toward females, and the age structure was younger than observed in other unharvested populations. Survival of adult females was estimated at 0.9 ±0.1, and fertility was estimated at 0.77 female young/female/year. Density on the study area was estimated at 0.21 bears/km2 and the current finite growth rate (λ) of the study population was estimated to be 1.11/year. Demographic characteristics of the Oklahoma population of black bears were similar to those of other recolonizing populations of large carnivores.

Tree invasion constrains the influence of herbaceous structure in grassland bird habitats

Abstract: Trees and other woody plants threaten grassland obligate birds, as well as the biological integrity of grasslands around the world. Bird species associated with grasslands of southern mixed-grass prairie of North America have declined in abundance, whereas species associated with shrub-stage and woodland habitats have increased. Recent increases in the extent of eastern redcedar (Juniperus virginiana) in the southern Great Plains of North America explain some of the change in bird assemblages in landscapes composed of patches of grassland fragmented by cropland and stands of eastern redcedar. In this study, we determined the influence of eastern redcedar, relative to the influence of structural attributes of the herbaceous layer, on bird assemblages within individual patches of grassland habitat. We indexed bird abundance within the breeding season with point counts on grassland patches with varying levels of invasion of eastern redcedar. Canopy cover of eastern redcedar explained a greater proportion of the composition of bird communities in these grasslands than structure of herbaceous vegetation. Species associated with grassland habitats generally declined in abundance, whereas species associated with shrub and woodland habitats increased as cover of eastern redcedar increased. Perhaps more important to conservation ecology, our data indicate that as canopy cover of eastern redcedar increased, variation in abundance of grassland birds decreased, indicating that canopy cover of eastern redcedar may constrain the local influence of herbaceous habitat structure on bird assemblages.

Scale-Dependent Effects of Landscape Structure and Composition on Diurnal Roost Selection by Forest Bats

Abstract Forest management affects the quality and availability of roost sites for forest-dwelling bats, but information on roost selection beyond the scale of individual forest stands is limited. We evaluated effects of topography (elevation, slope, and proximity of roads and streams), forest habitat class, and landscape patch configuration on selection of summer diurnal roosts by 6 species of forest-dwelling bats in a diverse forested landscape of the Ouachita Mountains, Arkansas, USA. Our objectives were to identify landscape attributes that potentially affect roost placement, determine whether commonalities exist among species in their response to landscape attributes, and evaluate the effects of scale. We modeled roost selection at 2 spatial scales (250- and 1,000-m radius around each roost). For each species, parameters included in models differed between the 2 scales, and there were no shared parameters for 2 species. Average coefficients of determination (R2) for small-scale models were generally higher than for large-scale models. Abundance of certain forest habitat classes were included more often than patch configuration or topography in differentiating roost from random locations, regardless of scale, and most species were more likely to roost in areas containing abundant thinned forest. Among topographic metrics, big brown bats (Eptesicus fuscus) were more likely to roost at higher elevations; roosts of big brown bats, northern long-eared bats (Myotis septentrionalis), and Seminole bats (Lasiurus seminolus) were influenced by slope; and big brown bats, evening bats (Nycticeius humeralis), and Seminole bats were more likely to roost closer to water than random. Northern long-eared bats and red bats (Lasiurus borealis) were more likely to roost closer to roads, whereas eastern pipistrelles (Perimyotis subflavus) were more likely to roost further from roads than random. Common parameters in most models included 1) positive associations with group selection (5 of 6 species) and thinned mature forest (4 species) at the small scale; 2) negative associations with unmanaged mixed pine–hardwood forest 50–99 years old at the large scale (4 species); 3) negative association with stands of immature pine 15–29 years old at the small scale (3 species); and 4) a positive association with largest patch index at the large scale (3 species). Our results suggest that, in a completely forested landscape, a variety of stand types, seral stages, and management conditions, varying in size and topographic location throughout the landscape, would likely provide the landscape components for roosting required to maintain a diverse community of forest bats in the Ouachita Mountains.

Fitness Costs and Benefits Associated with Dispersal in Northern Bobwhites (Colinus virginianus)

Abstract Movements and dispersal distances are fundamental aspects of ecology and evolutionary biology. Northern bobwhites (Colinus virginianus) generally are considered the least mobile of all gallinaceous species, but dispersal events of bobwhites (commonly referred to as “shuffling”) are well known. Although dispersal may be a key component in regulating population densities and inbreeding avoidance, few studies have attempted to explain relationships between dispersal, mortality and nest success in northern bobwhites. To examine these relationships, we monitored 957 radio-marked bobwhite from 1991 to 1996. Mean dispersal distance did not differ between sexes (P = 0.699). Mean dispersal distances of adults (2821 m) were shorter than those of juveniles (3411 m; P = 0.042). We found no sex- or age-related differences in survival rates among dispersers and non-dispersers. Despite associated risks with increased movement activity in unfamiliar areas, survival rate was 1.5-times greater for dispersers (Ŝ = 0.72) than non-dispersers (Ŝ = 0.50). Further, we found no relationships between nest success and dispersal distance, suggesting that dispersal distance had little influence on reproductive output of bobwhites. Thus, dispersers may play a key role in bobwhite population dynamics whereby declining populations escape extinction through recruitment from productive populations.

Sensitivity of condition indices to changing density in a white-tailed deer population.

The ways in which comprehensive condition profiles, incorporating morphometric, histologic, physiologic, and diet quality indices, responded to changes in density of a white-tailed deer (Odocoileus virginianus) population were examined. Changes in these condition indices were monitored in a northeastern Oklahoma deer herd as density declined from peaks of 80 and 72 deer/km2 in 1989 and 1990 (high-density) to lows of 39 and 41 deer/km2 in 1991 and 1992 (reduced-density), respectively. Compared to a reference population (6 deer/km2), deer sampled during high-density exhibited classic signs of nutritional stress such as low body and visceral organ masses (except elevated adrenal gland mass), low fecal nitrogen levels, reduced concentrations of serum albumin, elevated serum creatinine concentrations, and a high prevalence of parasitic infections. Although density declined by one half over the 4-yr study, gross indices of condition (in particular body mass and size) remained largely unchanged. However, selected organ masses, serum albumin and non-protein nitrogen constituents, and fecal nitrogen indices reflected improvements in nutritional status with reductions in density. Many commonly used indices of deer condition (fat reserves, hematocrit, total serum protein, and blood urea nitrogen) were not responsive to fluctuations in density.

Differential consumption of eastern red cedar (Juniperus virginiana) by avian and mammalian guilds: Implications for tree invasion

Abstract Increased abundance and distribution of eastern redcedar (Juniperus virginianus), a native species in the Great Plains, has been associated with changes in ecosystem functioning and landscape cover. Knowledge of the main consumers and dispersal agents of eastern red cedar cones is essential to understanding the invasive spread of the species. We examined animal removal of cedar cones in three habitats (tallgrass prairie, eastern red cedar and woodland-prairie margins) in the Cross Timbers ecoregion using three exclosure treatments during autumn and winter. Exclosure treatments excluded study trees from ungulates, from terrestrial rodents and ungulates or from neither (control). Loss of cones from branches varied by a habitat-time interaction, but was not affected by exclosure type. Loss of cones from containers located under experimental trees varied by a habitat-treatment-time interaction. In December and January, cone consumption from containers in no-exclosure treatments was highest in margins, followed by tallgrass prairie and eastern red cedar habitats. We conclude birds consumed the majority of cones from branches and small- and medium-sized mammals consumed cones on the ground. Both birds and mammals likely contribute to the spread of eastern red cedar but at different scales. Limiting invasion of eastern red cedar in forests may require early detection and selective removal of pioneer seedlings in cross timbers and other habitats that attract a high diversity or density of frugivores.

Seasonal variation in activity patterns of the endangered Ozark big-eared bat (Corynorhinus Townsendii Ingens)

Abstract We studied occupation and activity at a hibernaculum and a maternity cave used by the endangered Ozark big-eared bat (Corynorhinus townsendii ingens). Big-eared bats remained active throughout winter, with many individuals leaving and entering the hibernaculum during the first 2 h after sunset; however, no fresh guano was found on cave floors during winter. Big-eared bats used caves with the coldest internal temperatures in the region as hibernacula and also moved among caves throughout winter. The breakup of hibernating colonies in spring and the subsequent buildup of maternity colonies by adult females were gradual. Nightly activity patterns at the maternity cave changed throughout summer relative to parturition and maturation of young. Females returned to the maternity cave more frequently when their young were totally dependent on them for nourishment. As the young began foraging, females returned only once during the night, and eventually adults did not return to the cave until morning. Ozark big-eared bats emerged shortly after sunset, regardless of brightness at twilight or rainfall, but they emerged at a later time when the young could not fly.