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Results for “Northwestern Naturalist”

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65 records · Page 4Linked to original sources
USGS2008

Late-seasonal activity and diet of the evening bat (Nycticeius humeralis) in Nebraska

In North America, Nebraska represents part of the northwestern edge of the distribution for the evening bat (Nycticeius humeralis). To date, little information on this bat's natural history has been published from the state or from other parts of the Great Plains. Here we report on aspects of its natural history in Nebraska from 2 localities. In late summer and early autumn of 2006, we documented individuals farther west in Nebraska (Harlan County) than previously reported and determined that individuals fed mainly on Coleoptera and Hymenoptera. In 2006, evening bats appeared to migrate from Nebraska during late September-early October, and individuals were extremely fat, about 15 g, prior to migration. Evening bats likely are more widespread and common in south central Nebraska than previously documented. On 6 October 2005, we reported on an individual from eastern Nebraska (Douglas County), which represents the latest seasonal record of N. humeralis from the state.

Western North American Naturalist↗
USGS2005

Habitat preferences of migrant and wintering northern harriers in northwestern Texas

We studied habitat preferences of northern harriers ( Circus cyaneus) in four counties of the Southern High Plains of northwestern Texas from October 1989 to May 1995. Harriers generally arrived in late July and departed in April. They hunted over a variety of habitats in the study area but mainly in Conservation Reserve Program (CRP) grasslands and vegetated playa basins. CRP grasslands, playa basins, and shortgrass prairie were used disproportionately to their availability, whereas winter wheat was used less than its availability. Brown harriers (adult females or subadults of either sex) foraged in CRP about as often as adult males but more frequently in playas and prairies, whereas adult males foraged more in winter wheat. As underground water sources for irrigation continue to be depleted, agricultural practices are likely to change. Depending on how the land is used after irrigation ceases, harriers may benefit if CRP grasslands, vegetated playas, and shortgrass prairies persist. If dominant land use reverts to livestock grazing, however, the harrier population will be negatively affected.

Southwestern Naturalist↗
USGS2019

Effects of landscape characteristics on annual survival of Lesser Prairie-Chickens

Agriculture and development have caused landscape change throughout the southwestern Great Plains in the range of the lesser prairie-chicken ( Tympanuchus pallidicinctus ). Landscape alteration within the lesser prairie-chicken range may contribute to range contraction and population losses through decreases in survival rates. Our objectives were to determine if: (1) landscape configuration ( i.e ., the spatial arrangement of habitat) or composition ( i.e ., the amount of habitat), at the study-site scale, affected annual survival of females, (2) relationships exist between landscape context ( i.e ., landscape configuration and composition) and weekly survival to assess effects of landscape composition and configuration on lesser prairie-chicken populations, and (3) anthropogenic features influenced daily mortality risk. We captured 170 female lesser prairie-chickens and used very-high-frequency and GPS (Global Positioning System) transmitters to track their movement and survival for 2 y. We used known-fate survival models to test if landscape configuration or composition within three sites in Kansas were related to differences in female survival among sites. In addition we tested for relationships between weekly survival and landscape configuration or composition within home ranges. Finally, we used Andersen-Gill models to test the influence of distance to anthropogenic features on daily mortality risk. Differences in survival were evident between sites with differing landscape compositions as annual survival in Northwestern Kansas (Ŝ = 0.27) was half that of Clark County, Kansas (Ŝ = 0.56), which corresponded with 41.9% more grassland on the landscape in Clark County; landscape configuration did not measurably differ among sites. Survival was greater for prairie-chickens with home-ranges that had greater patch richness and in areas with 30% crop and 57% grassland. Female lesser prairie-chickens also experienced greater mortality risk closer to fences at patch edges. Further conversion of grassland landscapes occupied by lesser prairie-chickens should be avoided to reduce habitat loss and fragmentation thresholds that could affect survival. We suggest continued encouragement of Conservation Reserve Program enrollment in western areas of the lesser prairie-chicken range to maintain or increase the amount of grassland to increase annual survival.

Kansas↗
USGS2015

Tree mortality in mature riparian forest: Implications for Fremont cottonwood conservation in the American southwest

Mature tree mortality rates are poorly documented in desert riparian woodlands. I monitored deaths and calculated annual survivorship probability (P s ) in 2 groups of large (27–114 cm DBH), old (≥40 years old) Fremont cottonwood ( Populus fremontii Wats.) in a stand along the free-flowing Yampa River in semiarid northwestern Colorado. P s = 0.993 year-1 in a group ( n = 126) monitored over 2003–2013, whereas P s = 0.985 year -1 in a group ( n = 179) monitored over the same period plus 3 earlier years (2000–2003) that included drought and a defoliating insect outbreak. Assuming P s was the same for both groups during the 10-year postdrought period, the data indicate that P s = 0.958 year -1 during the drought. I found no difference in canopy dieback level between male and female survivors. Mortality was equal among size classes, suggesting P s is independent of age, but published longevity data imply that either P s eventually declines with age or, as suggested in this study, periods with high P s are interrupted by episodes of increased mortality. Stochastic population models featuring episodes of low P s suggest a potential for an abrupt decline in mature tree numbers where recruitment is low. The modeling results have implications for woodland conservation, especially for relictual stands along regulated desert rivers.

Colorado↗
USGS2002

Effects of cottonwood leaf beetle Chrysomela scripta (Coleoptera: Chrysomelidae) on survival and growth of Fremont cottonwood ( Populus fremontii ) in northwest Colorado

Greenhouse and field studies were used to assess the effects of a cottonwood leaf beetle ( Chrysomela scripta ) outbreak on growth and survivorship of Fremont cottonwood ( Populus fremontii ) along a segment of the Yampa River in northwestern Colorado. Exposure of greenhouse-reared seedlings to either 1 or 3 larvae reduced survivorship and the shoot and root masses of surviving seedlings. In the field sapling survivorship in unmanipulated, naturally established patches of saplings was inversely related to the intensity of beetle damage noted the previous year in both 1998–1999 and 1999–2000. Floodplain saplings treated with the insecticide esfenvalerate during two growing seasons added more height and radial growth than untreated saplings. Field observations in riparian stands along the Yampa River indicated that beetles preferentially oviposited and fed on cottonwood seedlings over saplings and mature trees during late summer. Taken together, the greenhouse and field studies suggest herbivory by C. scripta is a major determinant of Fremont cottonwood distribution and abundance at the Yampa River site. Repeated surveys detected few or no beetles in stands along the neighboring but regulated Green River. We hypothesize that flow regulation, by reducing P. fremontii seedling abundance, precludes C. scripta from reaching outbreak status along the Green River.

Colorado↗
USGS2003

Den site activity patterns of adult male and female swift foxes, Vulpes velox, in northwestern Texas

Activity of Swift Foxes ( Vulpes velox ) at den sites was studied in northwestern Texas during pup rearing seasons in 2000 and 2001 to determine role of males in parental care. Twenty-four percent of radio-collared females with a potential to breed successfully raised pups to eight weeks of age. We intensively monitored presence and absence of male and female Swift Foxes at two den sites each year. Females were present >2.6 times more at den sites than males during the pup rearing season. Female and male Swift Foxes largely stayed at dens during diurnal hours and were active away from dens during nocturnal and crepuscular hours. Females and males spent 12.4% and 3.0% more time at dens before pups emerged, than after pups emerged, respectively. Following depredation of one male parent, the female spent 29% less time at the den site. Decrease in time spent at the den by the female following loss of her mate suggested that loss of one parent might severely impact recruitment of Swift Foxes. Our observations indicated that intense Coyote ( Canis latrans ) depredation may severely impact pup-rearing success as well as the parental care within Swift Fox family groups.

Texas↗
USGS2007

Has climatic warming altered spring flowering date of Sonoran Desert shrubs?

With global warming, flowering at many locations has shifted toward earlier dates of bloom. A steady increase in average annual temperature since the late 1890s makes it likely that flowering also has advanced in the northern Sonoran Desert of the southwestern United States and northwestern Mexico. In this study, phenological models were used to predict annual date of spring bloom in the northern Sonoran Desert from 1894 to 2004; then, herbarium specimens were assessed for objective evidence of the predicted shift in flowering time. The phenological models were derived from known flowering requirements (triggers and heat sums) of Sonoran Desert shrubs. According to the models, flowering might have advanced by 20-41 d from 1894 to 2004. Analysis of herbarium specimens collected during the 20th century supported the model predictions. Over time, there was a significant increase in the proportion of shrub specimens collected in flower in March and a significant decrease in the proportion collected in May. Thus, the flowering curve - the proportion of individuals in flower in each spring month - shifted toward the start of the calendar year between 1900 and 1999. This shift could not be explained by collection activity: collectors showed no tendency to be active earlier in the year as time went on, nor did activity toward the end of spring decline in recent decades. Earlier bloom eventually could have substantial impacts on plant and animal communities in the Sonoran Desert, especially on migratory hummingbirds and population dynamics of shrubs.

Southwestern Naturalist↗
USGS2016

Evidence for range contraction of snowshoe hare in Pennsylvania

In Pennsylvania, Lepus americanus (Snowshoe Hare) is near the southern limits of its range and at risk of range contraction because of loss of early-successional forest and impacts of climate change. We used hunter-harvest data to investigate changes in the distribution of Snowshoe Hare in Pennsylvania (1983–2011), forest inventory and land-use data to assess changes in amount and distribution of early-successional forest (1988–2011), and occupancy modeling (2004) to identify habitat and climate variables that explain the current distribution of Snowshoe Hare. We determined presence of Snowshoe Hare based on visual sightings, observations of tracks, and DNA analysis of fecal pellets, and used repeated visits to sampling sites and occupancy models to estimate occupancy rates (Ψ). Hunter-harvest data indicated the range of Snowshoe Hare in Pennsylvania contracted towards northwestern and northeastern portions of the state. Based on occupancy modeling, Snowshoe Hare were most likely to occupy early-successional and mixed deciduous-coniferous forest types and areas with colder winter temperatures, which coincided with the distribution of hunter harvests. Among the 4 forest types, we estimated Ψ = 0.52-0.79 and Ψ = 0.10-0.32 where winter temperatures were coldest and warmest, respectively. Total forest loss was <1% during 1988-2011, and the loss of early-successional forest in the current and former range of Snowshoe Hares was similar as were mean patch size and a fragmentation metric of early-successional habitat. Thus, changes in forest characteristics did not explain the range contraction we observed. We used climate-model predictions and our occupancy model to predict that average occupancy probability across northern Pennsylvania may decline from 0.27 in 2004 to 0.10–0.18 by 2050–2059, depending on the climate model. The range of Snowshoe Hare in Pennsylvania has contracted to regions of Pennsylvania with the coldest winter temperatures and most persistent snowpack, and based on projected climate change, our results suggest further range contraction of Snowshoe Hare in Pennsylvania.

Pennsylvania↗
USGS2003

Ord's kangaroo rats living in floodplain habitats: Factors contributing to habitat attraction

High densities of an aridland granivore, Ord's kangaroo rat (Dipodomys ordii), have been documented in floodplain habitats along the Yampa River in northwestern Colorado. Despite a high probability of inundation and attendant high mortality during the spring flood period, the habitat is consistently recolonized. To understand factors that potentially make riparian habitats attractive to D. ordii, we compared density and spatial pattern of seeds, density of a competitor (western harvester ant, Pogonomyrmex occidentalis), and digging energetics within floodplain habitats and between floodplain and adjacent upland habitats. Seed density within the floodplain was greatest in the topographically high (rarely flooded) floodplain and lowest immediately after a spring flood in the topographically low (frequently flooded) floodplain. Seed densities in adjacent upland habitat that never floods were higher than the lowest floodplain habitat. In the low floodplain prior to flooding, seeds had a clumped spatial pattern, which D. ordii is adept at exploiting; after spring flooding, a more random pattern resulted. Populations of the western harvester ant were low in the floodplain relative to the upland. Digging by D. ordii was energetically less expensive in floodplain areas than in upland areas. Despite the potential for mortality due to annual spring flooding, the combination of less competition from harvester ants and lower energetic costs of digging might promote the use of floodplain habitat by D. ordii.

Southwestern Naturalist↗
USGS2007

Aquatic vertebrate assemblages of the upper Clear Creek Watershed, California

We sampled streams in the Upper Clear Creek Watershed in northwestern California in fall 2004 and fall 2005 to document assemblages of aquatic vertebrates and to provide resource managers with information on the importance of these assemblages in terms of regional biodiversity. We used single-pass backpack electrofishing to sample 15 sites in fall 2004 and the same 15 sites plus 4 new sites in fall 2005. We captured 10 fish taxa and 2 species of larval amphibians. Seven of the fish taxa were native species. Of the exotic species, only brook trout (Salvelinus fontinalis) occurred at more than 1 site. Ordinations by nonmetric multidimensional scaling indicated a gradient from sites with rainbow trout (Oncorhynchus mykiss), Pacific giant salamander (Dicamptodon tenebrosus), and tailed frog (Ascaphus truei) to sites dominated by riffle sculpin (Cottus gulosus), California roach (Hesperoleucas symmetricus), and Sacramento sucker (Catostomus occidentalis). The gradient in species composition was associated with changes in elevation, gradient, discharge, and substrate. The Upper Clear Creek Watershed represents a unique area of overlap between the North Coast California amphibian fauna and the Central Valley fish fauna with a notable paucity of exotic fishes and amphibians. Preservation of the integrity of native aquatic assemblages is an important goal for aquatic resource management in the region; our results provide a critcial baseline to gauge future management actions.

California↗
USGS2012

Associations of benthic macroinvertebrate assemblages with environmental variables in the upper Clear Creek watershed, California

Benthic macroinvertebrates are integral components of stream ecosystems and are often used to assess the ecological integrity of streams. We sampled streams in the upper Clear Creek drainage in the Klamath—Siskiyou Ecoregion of northwestern California in fall 2004 (17 sites) and 2005 (original 17 plus 4 new sites) with the objectives of documenting the benthic macroinvertebrate assemblages supported by the streams in the area, determining how those assemblages respond to environmental variables, assessing the biological condition of the streams using a benthic index of biotic integrity (IBI), and understanding the assemblages in the context of biodiversity of the ecoregion. We collected both reach-wide (RW) and targeted-riffle (TR) macroinvertebrate samples at each site. The macroinvertebrate assemblages were diverse, with over 150 genera collected for each sampling protocol. The macroinvertebrate assemblages appeared to be most responsive to a general habitat gradient based on stream size, gradient, flow, and dominance of riffles. A second important habitat gradient was based on elevation and dominance of riffles. A gradient in water quality based on concentrations of dissolved ions and metals was also important. Models based on these 3 gradients had Spearman's rank correlations with macroinvertebrate taxonomic composition of 0.60 and 0.50 for the TR and RW samples, respectively. The majority (>50%) of the sites were in good or very good biological condition based on IBI scores. The diversity of macroinvertebrate assemblages is associated with the diversity of habitats available in the Klamath—Siskiyou Ecoregion. Maintaining the aquatic habitats in good condition is important in itself but is also vital to maintaining biodiversity in this diverse and unique ecoregion.

California↗