Examining ecological consequences of feral horse grazing using exclosures

Although feral horses have inhabited western North America since the end of the 16th century, relatively little synecological research has been conducted to quantitatively characterize how they interact with ecosystem components. Because feral horses exhibit watering behavior markedly different from that of domestic cattle, it is particularly important to evaluate response of ecosystem elements near water sources to horse use. To assess this response, we performed live-trapping of small mammals and 2-tiered vegetative sampling in 2 mountain ranges in central Nevada in the interior Great Basin, USA. At low elevations, plots around horse-excluded springs exhibited notably greater plant species richness, percent cover, and abundance of grasses and shrubs, as well as more small mammal burrow entrances than plots at horse-grazed springs. At high elevations, meadows protected from grazing exhibited maximum vegetation heights 2.8 times greater than vegetation grazed by horses only and 4.5 times greater than vegetation grazed by horses and cattle. Species richness in quadrats was most different between the horse-and-cattle-grazed meadow and its ungrazed counterpart, suggesting the possibility of synergistic effects of horse and cattle grazing in the same location. This study, the first in the Great Basin to investigate quantitatively ecosystem consequences of feral horse use with exclosures, represents a preliminary step in identifying factors that determine the magnitude of horse grazing impacts.     

Influences of sex and weather on migration of mule deer in California

I examined differences by sex and influences of weather on timing and patterns of migration of Rocky Mountain mule deer ( Odocoileus h. hemionus ) in the eastern Sierra Nevada, California, during 1984-87. Deer initiated spring migration from the winter range at about the same time in all years and made extensive use of holding areas at intermediate elevations. Radio-telemetered deer showed strong fidelity to summer ranges over as many as four years. Fall weather produced different patterns of fall migration. Storms during October produced a pulsed migration, in which most animals mmiiggiraatteedd to the winter range during or soon after the storm; in a year without a storm, fall migration was gradual. Despite the influence of storms on the pattern of fall migration, the median date of fall migration by females did not vary over years; however, among males it was later in a year without fall storms.     

High foal mortality limits growth of a desert feral horse population in Nevada

A population of feral horses ( Equus caballus ) in the southern Great Basin Desert of Nevada was monitored from 1989 to 1998 to determine size, distribution, and population trends. All individual horses observed in the population were identified by unique markings during the first 2 yr of study, and most animals could be observed annually. During this study no new horses were identified in the population, indicating that no immigration occurred from outside populations. The population reached a high of 65 horses yearling or older in 1992 and declined each year thereafter, reaching a low of 36 horses in 1998. Estimated foal survival averaged < 12% over 8 yr. Only 11 horses were recruited into the population as yearlings or older animals during the study. Mountain lion predation is hypothesized as major factor limiting growth of this feral horse population.     

Demographic characteristics,seasonal range and habitat topography of Balkan chamois population in its southernmost limit of its distribution (Giona mountain,Greece)

The annual range of Balkan chamois (Rupicapra rupicapra balcanica) in Giona mountain was found to be 5502 ha, with a low population density (2 individuals/100 ha). Seasonal range patterns varied significantly, with a minimum extent in summer and a maximum in winter (30% and 79% of the annual range, respectively). Summer stress and the rutting period might be associated with the observed aggregated distributions during the summer and autumn (core areas of 28% and 22% of seasonal ranges, respectively, defined after the Fixed Kernel Density Estimator). Chamois were found to use significantly lower altitude habitats in winter (1212 m) than in summer (2223 m), and significantly steeper slopes in winter (35°); aspect was not found to have a significant effect on habitat use. Population structure consisted of kids (21%), yearlings (8%), females (35%) and males (36%). Conservation management for the species should consider poaching, livestock competition and global warming.     

Winter habitat selection patterns of Merriam's turkeys in the southern Black Hills, South Dakota

In northern areas of their expanded range, information on Merriam's turkeys ( Meleagris gallopavo merriami ) is lacking, specifically pertaining to wintering behavior and factors associated with winter habitat selection. Forest managers need detailed quantification of the effects of logging and other management practices on wintering habitats needed by Wild Turkeys and other wildlife. Therefore, we examined winter habitat selection patterns within ponderosa pine ( Pinus ponderosa ) forests and determined factors associated with use of farmsteads by Merriam's turkeys in the southern Black Hills, South Dakota. We radio-marked 86 female Merriam's turkeys (70 adults and 16 yearlings) and monitored them during winter (1 December–31 March), 2001–2004. Female Wild Turkeys used recently burned pine forest less than expected but selected farmsteads and stands of mature ponderosa pine ( 22.9 cm diameter at breast height [DBH] trees) for foraging sites. Within forests, female Wild Turkeys selected foraging sites with less understory vegetation and visual obstruction, and larger-diameter ponderosa pine. Ponderosa pine seed abundance varied among years, and pine seeds were most abundant in stands of 30–35 cm DBH with basal area of 22–28 m2 ? ha–1. Abundance of pine seeds may have influenced use of farmsteads by Wild Turkeys, more so than ambient temperatures or snow depth. In the southern Black Hills, management should emphasize open- to mid-canopy and mature-structural-stage pine stands, where seed production was greatest. During winters when mast from pine is unavailable, farmsteads likely provide nutritional supplementation and may be important for maintaining Merriam's turkey populations.     

Survival and reproduction of translocated Eastern Wild Turkeys in a sparsely wooded landscape in northeastern South Dakota

We studied the survival and reproduction of a newly introduced population of Eastern Wild Turkeys ( Meleagris gallopavo silvestris ) during 1999 and 2000 to determine the adaptability of this subspecies to a minimally wooded (<10%) region located north of their recorded historic distribution in South Dakota. During 1999 and 2000, the South Dakota Department of Game, Fish and Parks (SDGFP) released 111 female and 25 male turkeys from Iowa and Kentucky onto a study area in northeastern South Dakota. We used radio telemetry to monitor survival and reproduction of the females for 2 years after their initial release. Annual survival for 71 females averaged 67%. Seasonal survival was lowest in fall and highest in winter. Mortality agents included avian and mammalian predators, haying equipment, automobiles, and unknown causes. Nesting rate for the 2 years averaged 93%, and renesting rate of turkeys with failed 1st-nest attempts averaged 45%. Nest success for all nests was 50%, and 62% of females attempting to nest each year were successful in at least 1 attempt. Predation was the primary cause of nest failure during both years. Overall, 72% of brooding females successfully raised ≥1 poult to 4 weeks post-hatch while individual poult survival to 4 weeks posthatch averaged 36%. Despite <10% woodland cover, Eastern Wild Turkeys appeared to thrive in a glacial escarpment topography north of their historic range in the northern plains.     

Vegetal change on a northern Utah foothill range in the absence of livestock grazing between 1948 and 1982

Reexamination of a semiarid foothill rangeland, first evaluated in 1948, indicated that secondary succession continues to shift toward a perennial grass-forb community formerly dominated by xeric shrubs, particularly big sagebrush ( Artemisia tridentata spp. vaseyana ). The direct role in livestock grazing in establishment and maintenance of shrub-dominant plant communities appears confirmed in the decline of shrubs upon cessation of livestock grazing in summer and continued browsing by mule deer in winter. The reduction of shrub forages on mule deer winter ranges is a major factor in population declines.     

Population structure and breeding biology of the hairy crab Pilumnus vespertilio (Fabricius, 1793) (Crustacea: Brachyura: Pilumnidae) in southern Mozambique

The population structure and reproduction of Pilumnus vespertilio were studied for the first time in Mozambique. Random samples of crabs were taken monthly from January to December 2002 from a pebble area of Inhaca Island, southern Mozambique. A clear sexual dimorphism was observed in the present population with males reaching greater sizes than females. Sex ratio was female‐biased, and the monthly size–frequency distributions were often bimodal. The annual reproductive cycle of Pilumnus vespertilio was continuous with peaks of breeding in summer. Results suggest that embryonic development may be synchronized within the population as a result of the very high reproductive activity observed in summer. Juveniles are recruited mostly in winter in the study area.     

Population structure and reproductive biology of the fiddler crab Uca urvillei (Brachyura: Ocypodidae) in Maputo Bay (south Mozambique)

Although fiddler crabs are among the main faunal components in mangrove habitats, few studies have described the population structure and reproduction of tropical species. Such information is important for understanding their life cycle and ecology. In this study, the population structure and reproduction of Uca urvillei were studied at Costa do Sol, a tropical mangrove forest in Maputo Bay, southern Mozambique. Ten 1.0‐m² squares were sampled during low tide periods, between January and December 2003. The population is characterized by normal size distributions, which are slightly skewed to the left. Males on average are larger than females. Males were more abundant than females and the monthly sex ratios were male‐biased. Juveniles were found year‐round but were less common in June and December. Both gonadosomatic index and frequency of ovigerous females showed that Uca urvillei breeds continuously with peaks in summer and a strong decrease in winter. Egg number was proportional to female size.     

Brood-rearing habitat use by Rio Grande Wild Turkeys in Oregon

Wild turkey ( Meleagris gallopavo ) brood-rearing sites have been described for portions of their range, but brood-rearing habitat use and characteristics of brood-rearing sites used by Rio Grande Wild Turkeys ( M. g. intermedia ) in the Pacific Northwest were unknown. We described cover types at 362 brood-rearing sites and measured habitat characteristics at 64 of these sites used by a recently established Rio Grande Wild Turkey population in southwestern Oregon during May-September 1989 and 1990. Hens with broods used 9 of 10 available cover types. Meadows, mixed hardwood/conifer woodlands, and savannas were used more often than expected (47% of observations, P ≤ 0.05). Broods used mature mixed conifer and dense sapling/pole mixed conifer cover types less than expected and did not use brush-fields. Many brood-rearing sites were characterized by a parklike appearance. Understory vegetation averaged P ≤ 0.05). We suggest that land managers maintain mixed hardwood/conifer woodland and savanna cover types adjacent to meadows on south slopes to provide brood-rearing habitat for Rio Grande Wild Turkeys in southwestern Oregon.     

Effects of horse grazing in spring on survival, recruitment, and winter injury damage of shrubs

The use of domestic grazers to shift the growth advantage toward shrubs is a commonly applied tool on winter ranges managed primarily for big game. Results from horses grazing in spring indicated grazing also benefits shrub survival, seedling recruitment, and reduced winter injury damage on some species of shrubs.     

Evaluating the relationship between mule deer pellet-group data and available winter range, using LANDSAT imagery

In this study, mule deer population trend data (deer-days-use/hectare) were statistically analyzed with range area data that were extracted from LANDSAT satellite imagery. The remote sensing techniques developed use multidate, winter images of an area in central Utah. Snow-covered areas and vegetational areas mapped from the imagery were composited into 26 maps representing the approximate winter range available to mule deer on 26 dates over a five-year period (1972&ndash;1977). Utah State Division of Wildlife Resources pellet-group transect data were statistically analyzed with range data measured from the satellite imagery. Range area accounted for a fairly large proportion of the variation in deer-days-use/hectare (r = &ndash;.83). This result seems reasonable since deer population density should increase as available range decreases.     

Population cycles of Wahweap Milkvetch on the Henry Mountains and seed reserve in the soil

A population outbreak of Wahweap milkvetch ( A. lentiginosus var. wahweapensis Welsh) occurred in the Henry Mountains area of southeastern Utah in 1985 and 1986, causing extensive locoweed poisoning in cattle grazing these winter ranges. Weather conditions supporting this population outbreak included above average precipitation in the fall of 1984 and 1985, which presumably allowed germination of seed lying dormant in the soil. Above average spring precipitation in the subsequent year supported the population growth. Part of the population died in the summer of 1985, and nearly all plants died in the summer of 1986. Historically, population outbreaks occurred every six to eight years: 1949, 1957, 1965, 1973, 1979, and 1985-1986. Correlation with weather records indicated that population outbreaks occurred in years of high spring and total annual precipitation. Wahweap milkvetch seed lying dormant in the soil ranged from 940 to 4,346 seed/m 2 where old stands occurred, and 20 to 40 seed/m 2 where old plants were not evident. Sufficient seed remains in the soil to cause future population outbreaks.     

Population biology of Sphaeroma serratum Fabricius (Isopoda,Flabellifera) at the Port of Mar del Plata,Argentina

Variations in size distribution, sex ratio, fecundity and morph frequencies in a population of Sphaeroma serratum were studied year-round. Changes in size distribution are most marked during the breeding season. Growth is arrested during the winter months. Young are produced throughout the summer; these overwinter, reproduce and then die. Differences in size of mature males suggest an effect of the timing of birth on life-span. Females are able to produce two broods. Offspring number is positively correlated with female size. Brood pouch mortality is estimated at 39%. Marked changes in sex ratio within the breeding season are thought to be artifacts due to sexual differences in behaviour. Comparison of reproductive traits of this, and other, populations shows a latitudinal pattern related to the duration of the warm season. Analysis of morph frequencies revealed similarities with European populations so far studied.     

Ruffed grouse ( Bonasa umbellus ) foraging in aspen stands during winter in northern Utah

Ruffed Grouse ( Bonasa umbellus ) population densities are lower in the Intermountain West than elsewhere in the species' range. Throughout much of its range, the Ruffed Grouse is closely associated with quaking aspen ( Populus tremuloides ), in part because aspen buds are an important winter food. Because population fluctuations of Ruffed Grouse have been associated with changes in aspen abundance or chemical composition, we studied winter foraging of the species in the Intermountain West where it has received little attention. Aspen buds were the most prominent forage in the bird's diet, although in contrast to other Ruffed Grouse food habits studies, reproductive buds were not eaten more than vegetative buds, and buds of other deciduous plants were also important (>20% of the diet). Excretion of high concentrations of ammonium nitrogen suggests that grouse in northern Utah are ingesting higher levels of secondary plant compounds than reported elsewhere. Our results show aspen is important in the winter ecology of Ruffed Grouse in northern Utah and suggest that continued loss of aspen may impact grouse populations.     

Habitat use and selection and home ranges of Merriam's Wild Turkey in Oregon

Habitat use and selection by Merriam's Wild Turkeys ( Meleagris gallopavo merriami ) in Wasco County, Oregon, was studied during 1981-82. This turkey population selectively used forested cover types (such as ponderosa pine-Douglas-fir-oak, ponderosa pine-oak) characterized by a variety of structural features, species, and age classes. The population used single species forested cover types (oak, ponderosa pine) less than expected, used nonforested cover types in proportion to their availability, and avoided forested cover types with structure simplified by logging activities. The four age and sex classes had large seasonal home ranges (￣x = 1,615 ha); the smallest home ranges were exhibited by adult males in winter and the largest were shown by subadult males in fall. In most instances, turkeys used cover types as they were available. We suggest that structural complexity of vegetation, both within and among cover types, is an important component of habitat for Merriam's Wild Turkeys that should be considered in the evaluation of potential release sites and in habitat management plans.     

Comparison of vegetation patterns resulting from bulldozing and two-way chaining on a Utah pinyon-juniper big game range

Two adjacent mechanically treated pinyon-juniper ( Pinus spp. and Juniperus spp.) big game winter range sites in central Utah were sampled in 1981 to estimate vegetational differences and tree mortality from the two treatments. One site was treated by selectively bulldozing in 1957 and the other was double chained in 1965. Both treatments significantly reduced tree and litter cover, whereas significant increases were found for native grasses and shrubs compared to a nearby untreated site. Juniper cover for the untreated site was 35.5&#37; compared to only 1.4&#37; for the bulldozed area and 4.1&#37; for the two-way chained area. Browse species densities were increased by the mechanical treatments. The use of different mechanical treatments on separate smaller portions of critical areas of big game winter range would help provide: (1) for both long-term and short-term use of a critical wintering area, (2) greater overall productivity and carrying capacity, and (3) greater diversity by creating more edge effect between the differently treated and untreated areas.     

Seasonal trends and colonization patterns of macroinvertebrate assemblages in two streams with contrasting flow regimes

Patterns of colonization by macroinvertebrates were examined in two streams that differ in flow regime: a snowmelt system and a mesic groundwater system. Experiments were conducted during spring runoff, summer baseflow, and winter baseflow using artificial substrata. Colonization patterns reflected seasonal changes in benthic macroinvertebrate assemblages and life histories in each stream. The density and biomass of benthic organisms were approximately 3X greater in winter than in either spring or summer for both streams. Similarly, colonization was greater in winter than in spring or summer for both streams. In spring, colonization patterns were different between streams, with colonization being imperceptible in the snowmelt stream. Macroinvertebrate abundance fluctuated during the summer colonization experiment at both sites, resulting from a complex interplay among population emergence, recruitment, and/or movement. Assemblages in the snowmelt system primarily comprised mobile or ruderal taxa, such as Beatis tricaudatus and Chironomidae, whereas relatively sessile taxa, such as Glossoma nigrior , were predominant in the mesic groundwater system. Seasonal patterns of colonization differed among stream types primarily because of the profound interplay of flow regime and temperature on benthic community structure and organism life history.     

Diets of sympatric bobcats and coyotes during years of varying rainfall in central Arizona

We collected fecal samples (scats) of sympatric bobcats ( Lynx rufus ) and coyotes ( Canis latrans ) between 2000 and 2003 in a 53,600-ha area of the Upper Sonoran Desert in central Arizona. Our objective was to investigate composition, diversity, and overlap of diets of bobcats and coyotes in relation to varying rainfall in the Sonoran Desert of central Arizona. In general, bobcats ate more rodents than did coyotes, and coyotes ate more lagomorphs, large prey, and fruit/seeds than did bobcats. Composition of bobcat diets was independent of differences among years in annual rainfall and seasonal rainfall during summer–autumn (May–October) and winter–spring (November–April). Composition of coyote diets also was independent of drought conditions among years during summer–autumn, but coyotes ate more large prey and fewer rodents during years with winter–spring drought. Seasonally, bobcats ate more rodents than did coyotes in summer–autumn and winter–spring, whereas coyotes ate more lagomorphs than did bobcats during winter– spring, and more large prey and fruit/seeds in both seasons. Coyotes ate more large prey and lagomorphs during winter–spring, when seasonal rainfall was higher, and more fruit/seeds in summer–autumn, when seasonal rainfall was lower. Diversity of diets was consistently higher for coyotes than for bobcats, and increased for bobcats but not for coyotes during winter–spring drought and during higher seasonal rainfall in winter–spring. Overlap of diets between predators was independent of rainfall levels. We suggest that bobcats in the Sonoran Desert are more selective, specialized predators and that coyotes are more generalist, opportunistic predators. We hypothesize that, although diversity of bobcat food items and composition of coyote diets differ with varying rainfall in the Sonoran Desert, patterns of feeding strategy are independent of seasonal differences in precipitation and effects of drought, and bobcats and coyotes partition food resources independently of varying rainfall.