Brood parasitism and nest survival of Brown-headed Cowbird hosts at high-elevation riparian sites in the eastern Sierra Nevada, California

Deciduous riparian ecosystems in the western United States provide habitat for a higher density of breeding birds than reported for any other avian habitat type and provide habitat for more breeding bird species than adjacent uplands. On the east slope of the Sierra Nevada, riparian ecosystems make up Molothrus ater )—an obligate brood parasite that forages on bare ground and feedlots but typically commutes to distinct shrubland or woodland habitats for breeding. We examined nest survival, brood parasitism, breeding phenology, and causes of nest failure for birds at North Lake and Rock Creek: 2 high-elevation (>2500 m) riparian breeding habitats adjacent to recreational development and within cowbird commuting distance to additional potential foraging sites. Nest survival tended to be higher for host species at Rock Creek than for those at North Lake, but parasitism rates were not significantly different between plots. Of 21 open-cup nesting species, 12 were parasitized. We found the highest rate of parasitism (92%) for Warbling Vireos ( Vireo gilvus ) at North Lake, and parasitism contributed to lower total nest survival there (14%). For nearly all species, parasitized nests were less successful and produced fewer young than nonparasitized nests. However, predation was the leading cause of complete nest failure across all species and contributed to the lowest total nest survival estimates for Western Wood-Pewees ( Contopus sordidulus, 11%) and Dusky Flycatchers ( Empidonax oberholseri, 15%) at North Lake and for Dark-eyed Juncos ( Junco hyemalis, 15%) at Rock Creek. Nest survival was relatively high for Western Wood-Pewees (41%) at Rock Creek and for Yellow Warblers ( Dendroica petechia, 47%) at North Lake. We noted whether the arrival of pack animals at pack-station corrals contributed to variation in cowbird numbers at corrals or in parasitism rates at the 2 sites. Cowbirds occupied corrals before and after pack-stock arrival, and most host clutches were completed prior to pack-stock arrival at nearby corrals, suggesting that the presence of pack animals did not directly affect cowbird host species.     

Tree size and understory phytomass production in a western juniper woodland

Understory phytomass production in a western juniper ( Juniperus occidentalis ) woodland was examined relative to tree size in central Oregon in 1983 and 1984. Vegetation was sampled in two zones, the canopy zone (beneath the canopy) and the intercanopy zone (the space between canopies), on two adjacent sites—a lower slope site with shallow soil and an upper slope site with deeper soil. Sampling was stratified into three tree size classes. Individual species production was significantly affected by tree size and location relative to tree canopy. Production of bottlebrush squirreltail, bluebunch wheatgrass, cheatgrass, miscellaneous annual grasses, perennial forbs, and annual forbs increased with increasing tree size. Sandberg bluegrass production was greater in the intercanopy than the canopy zone, while production of bottlebrush squirreltail, bluebunch wheatgrass, miscellaneous annual grasses, and both perennial and annual forbs was greater in the canopy zone. Production of cheatgrass was determined by the interaction of tree size and zone. Phytomass relationships were expressed to a greater degree on the upper slope site, where total production exceeded that of the lower slope site by approximately 50% the second year of the study. Individual trees appear to exert a great influence on associated vegetation as western juniper woodlands progress from the seedling (tree establishment) phase to closed stands of mature trees. Original community dominants appear to be spatially segregated beneath tree canopies and associated with large trees, while formerly less common species, such as cheatgrass, come to dominate the entire site.     

Composition and abundance of periphyton and aquatic insects in Sierra Nevada, California, stream

The species composition of periphyton and benthic insect communities and abundances of common taxa (&;gt;0.1&;#37; of individuals) were examined during snow-free months in Convict Creek, a permanent snowmelt- and spring-fed stream in the Sierra Nevada of California. The communities were highly diverse. The most abundant taxa in the periphyton were diatoms ( Achnanthes minutissima, Cocconeis placentula lineata, Cymbella microcephala, C. sinuata, Fragilaria construens, F. crotonensis , Navicula spp., Synedra acus , and S. rumpens ), except in late spring and summer when several seasonal blue-green algae ( Chamaesiphon incrustans, Lyngbya spp. and Oscillatoria spp.) are at their maximum densities. Most common periphyton taxa vary systematically in abundance with season, but relative abundances of taxa also appear to be influenced by streambed scouring and by concentrations of ambient nutrients. Data on population densities and length frequencies of larval and nymphal stages of common benthic insects and occurrences of pupal and adult stages were examined to determine life history patterns. Taxa hatching in winter and spring and abundant as immatures in late spring include ephemeropterans ( Epeorus longimanus, Drunella flavilinea , and Caudatella heterocaudata ), plecopterans ( Calineuria californica, Doroneuria baumanni, and Pteronarcys princeps ) and dipterans ( Cryptolabis sp.). Common taxa hatching in late spring or summer are the plecopteran Malenka ( californica? ) and the trichopterans Arctopsyche grandis and Rhyacophila acropedes . Several bivoltine and multivoltine ephemeropterans ( Baetis devinctus and B. tricaudatus ) and dipterans ( Simulium spp. and Chironomidae) have summer cohorts. Taxa hatching in late summer or autumn and most abundant in autumn include ephemeropterans ( Baetis spp., Ephemerella infrequens, Epeorus dulciana, Ironodes lepidus , and Paraleptophlebia pallipes ), trichopterans ( Hydropsyche oslari, Lepidostoma spp., Glossosoma califica, Micrasema sp., Brachycentrus americanus, Neophylax sp., and Rhyacophila vaccua ) and dipterans ( Antocha monticola, Pericoma sp., and Chironomidae). Major recurring events that may influence life history patterns and structure of the benthic insect community are (1) near-freezing, nighttime winter water temperatures and occasional anchor ice, (2) a prolonged period of high discharge in late spring and early summer (3) a brief summer, and (4) a prolonged period of moderate stream discharge in autumn when the substratum is stable and food is abundant.     

Phytogeography and floristics of pinyon-juniper woodlands in northern Arizona

This study assesses the floristic diversity and affinities of pinyon-juniper (PJ) woodlands in northern Arizona at 2 different scales: regionally within the context of North American floristic patterns and locally within the 2500-m elevation gradient of the San Francisco Volcanic Field (SFVF). An analysis based upon 245 North American floras indicates that the PJ woodlands of the SFVF share strong affinities with the adjacent Colorado Plateau and Apachian floristic elements but also show high floristic similarity to the Great Plains. Data suggest that mid-elevation woodlands of the Colorado Plateau share floristic affinities with the Great Plains that are as strong as or stronger than those shared with the Great Basin. A geostatisical analysis provides a spatially explicit depiction of these findings. A comparison of species occurrences between 6 adjacent biotic communities in northern Arizona reveals that the PJ woodlands host the most distinctive flora among local life zones. Despite what their simple woodland structure may suggest, PJ woodlands of the SFVF host a moderately species-rich flora. This study suggests that the floras of PJ woodlands vary in significant and important ways across the range of PJ woodlands in western North America.     

Species composition and habitat associations of benthic algal assemblages in headwater streams of the Sierra Nevada, California

Despite their trophic importance and potential importance as bioindicators of stream condition, benthic algae have not been well studied in California. In particular there are few studies from small streams in the Sierra Nevada. The objective of this study was to determine the standing crop of chlorophyll- a and benthic algal species assemblages present in the small 1st- and 2nd-order streams of the Kings River Experimental Watersheds (KREW, watersheds of Bull, Providence, Duff, and Teakettle Creeks) and determine the associations of these measures with stream habitat. We collected samples of benthic algae from rock substrata in September 2002 (7 sites) and 2005 (the same 7 sites plus 5 additional sites). Habitat and water-quality data were collected concurrently. Chlorophyll- a values ranged from 0.2 to 3.2 mg ? m –2 . Chlorophyll- a in the Bull Creek watershed was generally lower than in the other watersheds. Benthic algal assemblages were dominated by diatoms and cyanobacteria. We collected 79 taxa of diatoms in 2002 and 126 taxa in 2005. Diatom taxa richness in individual samples ranged from 15 to 47. Nonmetric multidimensional scaling analysis of arcsine square-root transformed proportional abundances of diatoms identified 3 groups of sites. Bull Creek sites were generally different from other sites (group 1), and the sites from Bull Creek were different in 2002 (group 2) and 2005 (group 3). Five taxa appeared to be particularly important in distinguishing groups: Achnanthidium minutissimum , Cocconeis placentula , Eunotia incise , Eunotia pectinalis var. minor , and Planothidium lanceolatum . Elevation, water temperature, pH, specific conductance, and canopy were habitat variables correlated with the differences in diatom assemblages among sites. Our results provide a valuable baseline for future studies of benthic algae in Sierra Nevada headwater streams and will be particularly important in understanding the effects of different forest restoration management strategies being tested in the KREW project.     

Foliage biomass and cover relationships between tree- and shrub-dominated communities in pinyon-juniper woodlands

Woodlands dominated by singleleaf pinyon ( Pinus monophylla Torr.and Frem.) and Utah ( Juniperus osteosperma [Torr.] Little) cover extensive areas in the Great Basin and Southwest. Both species are aggressive and can nearly eliminate the previous shrub-dominated community. Successional pathways from shrub-dominated communities before tree establishment to the tree-dominated communities that follow are known only for a few specific sites. How site growing conditions affect successional patterns needs further study. We compared the relationship of foliage biomass and percentage of cover between paired shrub-dominated and tree-dominated plots over several sites. Sites studied are from different elevation and topographic conditions on one mountain range. Foliage biomass in shrub-dominated plots had about a three-to-one variation over the range of site conditions sampled. Tree-dominated plots varied by about two-to-one. Cover in shrub-dominated plots had a four-to-one variation; cover in the tree-dominated plots varied by about two-to-one. Total foliage biomass in both tree- and shrub-dominated plots correlated best with the site index of height at 200 years of age. Variation in percentage of cover in both tree and shrub-dominated plots correlated best with elevation. Foliage biomass variation in shrub-dominated plots was proportional to the variation in the paired tree-dominated plots. A similar proportional relationship was present for percentage of cover between paired tree- and shrub-dominated plots. Foliage biomass was more sensitive to topographic differences than to cover. Variation in plant species sampled in the shrub-dominated plots correlated with total foliage biomass of the same plots. Species sampled also correlated with pinyon height at 200 years of age and total foliage biomass in the paired tree-dominated plots.     

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% compared to only 1.4% for the bulldozed area and 4.1% 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.     

Observations on seasonal variation in desert arthropods in central Nevada

Pitfall and Malaise trap collections from terrestrial arthropod populations in central Nevada were analyzed for four trapping periods during the 1978 growing season. Mites (Acarina) and ants (Formicidae) were the taxa represented by the largest numbers of individuals in pitfall trap collections throughout the season; Malaise collections were composed mainly of aerial taxa (largely Diptera and Hymenoptera). Peak arthropod abundance was recorded during mid-June. Collection diversities for both trapping methods were generally low due to the abundance of a few taxa. Evidence for spatial heterogeneity in arthropod populations was meager; temporal heterogeneity in these populations, however, was more apparent.     

Observations on the ecology and trophic status of Lake Tahoe (Nevada and California, USA) based on the algae from three independent surveys (1965-1985)

Numerous physical, chemical, and biological criteria evidently confirm that Lake Tahoe is oligotrophic. However, detailed examination of the ecology and trophic status status of algae (mostly diatoms) from Lake Tahoe taken from three independent, long-term sampling programs aided in interpretation of plankton and periphyton algal communities by spectral analysis (supported by computerized data synthesis) and "ultra-oligotraphic" lakes over the world from which future studies may reveal algal communities that may be described as more mesotrophic and/or eutrophic than oligotrophic. Lake Tahoe probably is not as oligotrophic as is generally believed, and the indicator algae in it are not as accurate as is generally believed.     

Bat distribution and hibernacula use in west central Nevada

We captured 299 individuals of 11 bat species in mist-nets at 18 water sources in west central Nevada from June through August 1994. Myotis ciliolubrum, Pipistrellus hesperus, M. californicus , and Corynorhinus townsendii were the most common species captured. These species are apparently broadly distributed throughout west central Nevada, occurring in a variety of habitat types. We captured Euderma maculatum at 2 localities. These represent the 1st known records of this species in Esmeralda County, Nevada. Mine adits were surveyed for hibernating bats from December 1994 through February 1995. We determined the presence of 3 hibernating species: C. townsendii, M. ciliolabrum and P. hesperus . Bats were present in 19 of 70 mines (27%) we surveyed at elevations ranging from 1500 m to 2460 m. C. townsendii was the most common species encountered. Our study provides some much-needed baseline data on bat distribution and use of mines for hibernacula in west central Nevada.     

Classification and ordination of Coleogyne communities in southern Nevada

Woody plant community composition was analyzed throughout the range of Coleogyne ramosissima in the Spring and Sheep Mountain ranges of southern Nevada. The lower Coleogyne elevational boundary was analyzed in detail in Lucky Strike Canyon, on the eastern edge of the Spring Mountains. TWINSPAN (2-way indicator species analysis) identified 4 primary species and stand groups from the 2 mountain ranges (extensive survey). Analysis of DECORANA (detrended correspondence analysis) results indicated that elevation and soil depth were the environmental factors most significantly associated with distribution of species and stand groups in the extensive survey. Elevation was the only significant physical factor associated with distribution of species and stand groups in the intensive survey. Five vegetation zones form the 2 mountain ranges were identified based on their dominant species in 15 extensive transects. Coleogyne were subdivided into pure stands and upper and lower ecotones for further investigation of species distribution and environmental factors. Selected environmental factors appear to play an important role in structuring the Mojave Desert vegetation zones in southern Nevada.     

New Nevada entities and combinations in Eriogonum (Polygonaceae)

New species and varieties of the plant genus Eriogonum (Polygonaceae) that occur in Nevada are proposed. Eriogonum tiehmii and E. ochrocephalum var. alexanderae are endemic to Nevada, and E. lewisii is restricted to extreme northeastern Nevada and adjacent Utah. These entities belong to the subgenus Eucycla. Two varieties of E. umbellatum (of the subgenus Oligogonum) are proposed. The first, var. juniporinum , is found in eastern Nevada and in the desert ranges of southeastern California. The second is var. furcosum , which is restricted to the Sierra Nevada. One new combination is also proposed: E. nudum var. gramineum .         

Review of selenium in soils, plants, and animals in Nevada

Selenium is critical in livestock nutrition; forage can be either potentially deficient or toxic in this element. Selenium is accumulated in excessive amounts by a relatively few species of plants. Several of these plants, termed indicator species, occur in the western Great Basin; however, selenium toxicity is not a problem in Nevada for domestic livestock. The detection of marginal dietary deficiencies of selenium is of much greater economic importance to the livestock industry than an excess of this element. Selenium occurs as a trace element in the composition of various minerals. Selenium levels are very low in volcanic rocks of recent origin. Accumulations of this element require concentration through secondary dispersion and subsequent sedimentation. Therefore, excesses of selenium are usually associated with siltstone, sandstone, or other sedimentary rocks. Selenium is usually found in soils as selenate, a water-soluble mineral. The selenium concentration of plants is directly related to the selenate concentration in soil. In soils low in selenate, the ability of plants to accumulate selenium is similar. In soils with high levels of selenate, indicator species accumulate 10 times as much selenium as other species. The foliage of most indicator plants is generally avoided by grazing animals. Deficiencies in dietary selenium are associated with the occurrence of white muscle disease, retained placentas, and general unthriftiness of animals. Insufficient dietary selenium can be overcome through injection, intraluminal pellets, or supplementation with salt mixtures.     

Western diamondback rattlesnake in southern Nevada: a correction and comments

Reports of the occurrence of Crotalus atrox Baird & Girard from Nevada are reviewed. There is no evidence to support the occurrence of this species in Nevada.     

Impact of cattle on two isolated fish populations in Pahranagat Valley, Nevada

The presence of cattle at Browning Spring and Ash Springs in Pahranagat Valley, Nevada, impacted fish populations by causing an increase in ammonia (NH 3 ) and nitrite (NO 2 ) levels, an increase in Pseudomonas aeruginosa and Aeromonas hydrophila , and increased, mortality and morbidity. One of the affected fishes, the White River springfish, is listed as endangered by the Department of the Interior. After removal of the cattle from Ash Springs, NH 3 and NO 2 levels decreased and fish populations increased. At Brownie Spring the NH 3 and NO 2 levels are chronically elevated, cattle are still present, and the speckled dace population has not recovered.     

Grasshopper densities on grazed and ungrazed rangeland under drought conditions in southern Idaho

Low-density grasshopper populations were sampled at 15 pairs of rangeland sites in south central Idaho. One site of each pair had not been grazed by livestock for at least 10 years. Grazed sites were managed under normal grazing regimes established by the Bureau of Land Management. Mean grasshopper density was higher on ungrazed sites than on grazed sites. Proportions of Melanoplus sanguinipes were higher on ungrazed sites than on grazed sites and were higher on annual grasslands than on other vegetation types. Effects of grazing appeared to be independent of vegetation type. Proportions of Comhpocerinae, a subfamily of grasshoppers that feeds almost exclusively on grasses, were affected by vegetation type, but not grazing. Crested wheatgrass seedings supported the highest proportions of Gomphocerinae. Proportions of Oedipodinae were affected by grazing and vegetation type. Higher proportions of Oedipodinae were found on grazed sites than on ungrazed sites, and on sagebrush/grass sites than on annual grasslands. Results indicate that livestock grazing during drought conditions tends to reduce grasshopper populations in southern Idaho rangeland.     

Breeding records for Clark's Grebe in Colorado and Nevada

Described as a new breeding species is Clark's Grebe in Colorado and Nevada.     

Behavioral activities and breeding success of Willow Flycatchers in the Sierra Nevada

Observing survival and how individuals allocate time can provide insight into a species' ability to tolerate environmental constraints. We studied the Willow Flycatcher ( Empidonax trallii ) in the Sierra Nevada to determine if there were behavioral differences between pairs that successfully produced offspring and those that did not. This information will advance understanding of why these birds are declining in the Sierra Nevada and contribute to recommendations that may help to conserve them. We studied birds in 13 meadows in 2000 and 2001 using continuous focal-animal observations. Of the 43 territories we observed, 11 were occupied by males who never paired with a female, leaving 32 pairs for analysis. Of the 32 pairs, 13 were successful at breeding on their 1st attempt, and 9 pairs failed at their initial try but were successful on their 2nd breeding attempt. Throughout the breeding season, Willow Flycatchers spent 77%-78% of the day loafing during territory establishment and nest building, and loafing reached a low of 49% of the time budget during the nestling stage. Unsuccessful pairs spent on average 34% more time perching than their successful counterparts, while successful pairs spent on average 48% more of their time on the nest than unsuccessful pairs. Willow Flycatchers doubled the time spent foraging during the nestling phase because they had to meet the daily intake requirements for their young and themselves. Our results suggest that birds that spent more time on the nest and less time vocalizing had a significantly higher probability of successfully producing young because they were able to protect nests from predators, nest parasites, and inclement weather.     

Regional and seasonal diet of the Western Burrowing Owl in south central Nevada

We examined diets of Western Burrowing Owls ( Athene cunicularia hypugaea ) based on contents of pellets and large prey remains collected year-round at burrows in each of the 3 regions in south central Nevada (Mojave Desert, Great Basin Desert, and Transition region). The most common prey items, based on percent frequency of occurrence, were crickets and grasshoppers, beetles, rodents, sun spiders, and scorpions. The most common vertebrate prey was kangaroo rats ( Dipodomys spp.). True bugs (Hemiptera), scorpions, and western harvest mice ( Reithrodontomys megalotis ) occurred most frequently in pellets from the Great Basin Desert region. Kangaroo rats ( Dipodomys spp.) and pocket mice (Perognathinae) were the most important vertebrate prey items in the Transition and Mojave Desert regions, respectively. Frequency of occurrence of any invertebrate prey was high (>80%) in samples year-round but dropped in winter samples, with scorpions and sun spiders exhibiting the steepest declines. Frequency of occurrence of any vertebrate prey peaked in spring samples, was intermediate for winter and summer samples, and was lowest in fall samples. With the possible exception of selecting for western harvest mice in the Great Basin Desert region, Western Burrowing Owls in our study appeared to be opportunistic foragers with a generalist feeding strategy.     

Biotic and abiotic factors influencing the distribution of Coleogyne communities in southern Nevada

Woody plant community composition was analyzed throughout the range of Coleogyne ramosissima in the Spring and Sheep Mountain ranges of southern Nevada. The lower Coleogyne elevational boundary was analyzed in detail in Lucky Strike Canyon, on the eastern edge of the Spring Mountains. TWINSPAN (2-way indicator species analysis) identified 4 primary species and stand groups from the 2 mountain ranges (extensive survey). Analysis of DECORANA (detrended correspondence analysis) results indicated that elevation and soil depth were the environmental factors most significantly associated with distribution of species and stand groups in the extensive survey. Elevation was the only significant physical factor associated with distribution of species and stand groups in the intensive survey. Five vegetation zones form the 2 mountain ranges were identified based on their dominant species in 15 extensive transects. Coleogyne were subdivided into pure stands and upper and lower ecotones for further investigation of species distribution and environmental factors. Selected environmental factors appear to play an important role in structuring the Mojave Desert vegetation zones in southern Nevada.