Distribution and dynamics of waterbird habitat during spring in southern Oregon–northeastern California

The southern Oregon–northeastern California and extreme northwestern Nevada (hereafter “SONEC”) region provides critical spring migration habitat for waterfowl and other waterbirds in the Pacific Flyway. Information on the dynamics and distribution of waterbird habitats in SONEC during spring is needed to guide conservation efforts in the region. We grouped 1992 National Land Cover Data classes into 5 potential waterbird habitat types and used Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus satellite imagery to map flooding of these habitat types in SONEC during February–May, 2002 and 2003. SONEC included 13,727 km 2 of potential waterbird habitat comprised of grasslands (37.1%), pasture/hay (24.6%), marsh (15.9%), open wetland (11.8%), and croplands (10.6%). On average, 11.9% of this potential habitat was flooded during spring; but the percentage, area, and composition varied within and among years and subregions. Total flooding increased from 693 km 2 in February to 2099 km 2 in April during 2002 and from 1630 km 2 in February to 2125 km 2 in May during 2003. Open wetland comprised 58%–74%, marsh 8%–18%, pasture/hay 4%–11%, grassland 4%–17%, and cropland 3%–8% of the flooded habitat in SONEC. Satellite imagery and land-use data provided useful estimates of waterbird habitat availability in SONEC during spring, but other methods should be tested to more accurately measure flooding of densely vegetated habitats such as marsh. With <12% of the potential habitat flooded on average during spring, conservation programs have ample opportunity to improve the SONEC landscape for migrating waterbirds.     

Nesting ecology of waterbirds at Grays Lake, Idaho

Montane wetlands provide valuable habitat for nesting waterfowl and other waterbirds in the western United States, but relatively little information is available about the nesting ecology of their waterbird communities. We describe the general nesting ecology of breeding waterbirds at a large, shallow, montane wetland in southeastern Idaho during 1997-2000. Habitats include upland grasslands and intermittently to semipermanently flooded wetland habitats. We located a total of 1207 nests of 23 bird species: Eared Grebe ( Podiceps nigricollis ), Canada Goose ( Branta canadensis ), Mallard ( Anas platyrhynchos ), Gadwall ( A. strepera ), American Wigeon ( A. americana ), Green-winged Teal ( A. crecca ), Blue-winged Teal ( A. discors ), Cinnamon Teal ( A. cyanoptera ), Northern Shoveler ( A. clypeata ), Northern Pintail ( A. acuta ), Redhead ( Aythya americana ), Canvasback ( A. valisineria ), Lesser Scaup ( A. affinis ), Ruddy Duck ( Oxyura jamaicensis ), Northern Harrier ( Circus cyaneus ), American Coot ( Fulica americana ), Virginia Rail ( Rallus limicola ), Greater Sandhill Crane ( Grus canadensis tabida ), American Avocet ( Recurvirostra americana ), Long-billed Curlew ( Numenius americanus ), Wilson's Snipe ( Gallinago delicata ), Wilson's Phalarope ( Phalaropus tricolor ), and Short-eared Owl ( Asio flammeus ). Most nests were initiated in May-early June and were terminated (hatched or destroyed) by the 3rd week of June. Mean daily survival rate (DSR) for Canada Goose nests was 0.954 ± 0.005 ( s ￣x ; n = 127 nests), equivalent to Mayfield nest success of 21%. Mean DSR for dabbling duck nests over all 4 years was 0.938 ± 0.006 ( n = 41), equivalent to Mayfield nest success of 11%. For all other species where we found > 10 nests each year (Eared Grebe, Redhead, Canvasback, Coot, Sandhill Crane, American Avocet, and Wilson's Snipe), > 50% of nests found hatched at least 1 young. Success rates for geese, cranes, and ducks were lower than reported for Grays Lake during 1949-1951 and lower than most other wetlands in the region.     

Effects of prescribed fall burning on a wetland plant community, with implications for management of plants and herbivores

An important contemporary challenge for adaptive resource management is assessing both the direct and indirect effects of management activities by designing appropriate monitoring programs and sound analysis methods. Here we evaluate the effects of prescribed fall burning on a wetland plant community that is managed primarily for spring-migrating geese. During late fall in 2 consecutive years, we burned vegetation in 4 replicate blocks (2.3 ha each) that traversed a natural moisture and associated vegetation gradient. We used ordination, gradient analysis, and contingency table analysis to evaluate how annual changes in relative abundance of plants were affected by burning as well as other important ecological factors. Burning increased species diversity of plants, especially in the 2 wetter vegetation zones, but had no effect on species richness or on the proportion of native plant species. Wetland plant species responded to prescribed burning independently, and their response often differed by vegetation zone and with annual variation in flooding. Burning enhanced the abundance of native foxtail barley ( Hordeum jubatum ) and reduced the abundance of introduced swamp timothy ( Crypsis shoenoides ). Saltgrass ( Distichlis spicata ), a native plant species, was usually less abundant following burning, although the level of response was different for each of the 3 vegetation zones. Two other introduced plant species, quackgrass ( Elytrigia repens ) and reed canarygrass ( Phalaris arundinaceae ), were less abundant after fall burning, especially when spring flooding was more extensive. Wild geese using the experimental blocks for feeding clearly preferred burned sites, suggesting that fall burning can enhance wetland use by geese during spring. Given that simple manipulations such as burning and flooding of a wetland system may often produce complex results, we suggest that on-going management schemes be regularly evaluated with field experiments such as those conducted in this study.     

Winter survival of Northern Pintails in the Middle Rio Grande Valley, New Mexico

In response to continued low population numbers of Northern Pintail ( Anas acuta ) in North America and to increase knowledge of the geographic variation in pintail survival rates, we estimated 126-day (27 October–2 March) survival for male and female pintails wintering in the Middle Rio Grande Valley, New Mexico, during 2001–2002 (SY1) and 2002–2003 (SY2). Sixty-nine adult male and female pintails were marked with radio-transmitters and tracked throughout the study period. Weekly relocation data in relation to study year, sex, time (week), body condition at capture, and hunting seasons were modeled using the known-fate procedure in Program MARK. Year, sex, time, and body condition covariates did not improve model performance in estimating survival, so we used the most parsimonious model to produce an overall winter survival estimate of 0.597 ± 0.077 (95% C.I. = 0.442–0.735). Weekly survival estimates did not differ between hunting and nonhunting seasons. Male and female point estimates did not differ (χ 1 2 = 0.209, P = 0.65). Our adult female survival estimate of 0.639 ± 0.117 (95% C.I. = 0.396–0.827) was 5.5%–28.6% lower than published estimates for adult female pintails in 5 other geographic regions. No winter survival estimates for males in other geographic regions were available for direct comparison with our study. Although relatively small sample sizes may have contributed to the lack of statistical differences in weekly survival between years, sexes, and hunting seasons, as well as to the lack of influence of body condition, relatively abundant water and food resources and absence of hunting in a refuge setting contributed to consistent survival probabilities. Because our low survival estimates, relative to other geographic regions, cannot be attributed to hunting, we postulate that natural causes of mortality play a larger role in pintail survival in our study region than in other wintering regions.     

Interannual abundance of nonnative fathead minnows ( Pimephales promelas ) in Upper Klamath Lake, Oregon

Since its introduction about 20 yr ago, fathead minnow ( Pimephales promelas ) has become very abundant in Upper Klamath Lake, Oregon. In 1991 mean bench seine catch per unit effort (CPUE) was 214, compared to 25 for native blue chub ( Gila coerulea ), the next most abundant species. In 45 trap-net samples collected in 1992, fathead minnow constituted 59% of the fishes caught in Agency Lake subbasin, 27% in Upper Klamath Lake, and 17% in tributary inflow habitats. From 1991 to 1995 fathead minnow declined and the abundance of some native fishes increased. Introduction to Klamath Basin was coincident with U.S. Environmental Protection Agency of fathead minnow as bioassay subjects. Upper Klamath Lake fathead minnow have incomplete lateral lines and males have mandibular tubercles, diagnostic of the northeastern subspecies. Although the origin, as bait bucket transfer, forage fish, or laboratory release, cannot be determined with certainty, the possibility of laboratory release suggest modification of bioassay protocols to require destruction of test or excess subjects.     

Populations and habitat relationships of Piute ground squirrels in southwestern Idaho

Piute ground squirrels ( Spermophilus mollis idahoensis ) are normally above ground from late January until late June or early July in the Snake River Birds of Prey National Conservation Area in southwestern Idaho. In 2002 they were rarely seen above ground after early May. Because of the ecological importance of ground squirrels for nesting raptors and other species, we sought to determine the reasons for their early disappearance. We sampled 12 sites from January 2003 through March 2003 to determine if a population crash had occurred in 2002. Tests indicated that Piute ground squirrels had not been exposed to plague within the past year. The presence of yearlings in the population indicated that squirrels reproduced in 2002 and that at least some yearlings survived the winter. Both yearling and adult squirrels appeared to be reproducing at or above normal rates in 2003. The most plausible explanation for the early disappearance of Piute ground squirrels in 2002 is that squirrels entered seasonal torpor early in response to a late spring drought. In addition, the breeding chronology of squirrels may have shifted during the past 2 decades in response to climate change and/or habitat alteration. Shrub habitats provide a more favorable and stable environment for squirrels than grass habitats. Squirrel abundance was higher on live-trapping grids with sagebrush than on grids dominated by grass, and squirrel masses were higher at sites dominated by shrubs and Sandberg bluegrass ( Poa secunda ). Densities in big sagebrush ( Artemisia tridentata ) were within the ranges reported for earlier years, but densities in grass were lower than previously reported. Low densities at grassland sites in 2003 support other findings that drought affects squirrels in altered grass communities more than those in native shrub habitats. Long-term shifts in ground squirrel breeding chronology may have implications for raptors that depend on them for food.     

Seasonal habitat use and selection of Chukars in west central Idaho

We examined radio-marked Chukar ( Alectoris chukar ) habitat use and selection in west central Idaho during spring and summer of 1995 and 1996. Use of habitats also was compared with abundance and distribution of yellow starthistle ( Centaurea solstitialis ), an exotic species that is increasingly abundant in Chukar habitats. During summer Chukars used areas of southeast aspect 12% less ( P = 0.002) and areas of northwest aspect 11% more ( P = 0.008) than in spring. Chukars also used areas that averaged 9% steeper slopes ( P P = 0.054) in summer than in spring. Shrub cover types were used 22% more ( P P P P P < 0.05) than expected, implicating the detrimental effects of this exotic plant on habitat use of Chukars.     

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.     

Breeding ecology of White-faced Ibis ( Pleagadis chihi ) in the Upper Klamath Basin, California

The White-faced Ibis ( Plegadis chihi ) is a California state and U.S. Fish and Wildlife Service species of special management concern. We studied White-faced Ibis breeding ecology from May through July 1995 on Lower Klamath National Wildlife Refuge (NWR) in the upper Klamath Basin of California. A total of 2029 pairs nested in 3 colonies exclusively in early-successional hardstem bulrush ( Scirpus acutus ). Nest initiation dates ranged from 10 May to 12 June, and mean clutch size was 3.16. Reproductive success averaged 87% apparent nest success ( n = 115), 82% hatchability, 97% whole and partial brood survival, and 2.39 fledglings per successful nest. Mayfield estimates of nest survival were 79.1% during the laying and incubation period and 95% during the nestling period. Overall nest success as estimated by the Mayfield method was 75.4%. Our estimates of nest success are some of the highest reported anywhere in the literature for White-faced Ibis. Therefore, Lower Klamath NWR may maintain preferred White-faced Ibis breeding habitats in years of otherwise poor habitat conditions across the Intermountain West.     

Seasonal abundance and life cycle of Archaeomysis articulata (Crustacea: Mysidacea) on a sandy beach of western Hokkaido,Japan

Abundance and life cycle of the sandy beach mysid Archaeomysis articulata Hanamura were investigated based on seasonal collections over 2 years in the surf-swept intertidal zone of an open sandy beach in Ishikari Bay, western Hokkaido, Japan. The number of mysids in the intertidal zone increased from winter to spring, reaching its maximum in summer to autumn (average >2500 ind. m^-2), and decreased considerably towards the end of the year. The abundance was maintained at a minimal level (<200 ind. m^-2) throughout the winter. The breeding season was March to November, during which the liberation of young was most intensive from late April to mid-October. Three alternate generations, including overwintering, spring and summer generations, were suggested from field observations. Archaeomysis articulata is primarily iteroparous; only a restricted number of breeding females could produce more than two broods. The life span was estimated to be 7–9 months for the overwintering generation and 2.5–3.5 months for the spring–summer generations. The sex ratio fluctuated at samplings, with a tendency toward female dominance (overall mean=54%). The number of embryos carried by a single female ranged from 16 to 94, tending to increase with increasing size of females. The size of egg-like embryos varied seasonally from 0.45 to 0.54mm, being largest in spring and smallest in summer, with no correlation to the length of females; water temperature is considered an important factor in regulating the size of eggs. The embryonic development time was estimated to be 1.5 months for the spring generation (water temperature 5–10°C), and much shorter than this for the summer and overwintering generations. The mortality rate during embryonic development was estimated to be 7–18%.     

Winter and early spring bird communites in grasslands, shrubsteppe, and juniper woodlands in central Oregon

We compared winter (December, January, and February) and early spring (March and April) bird communities among 4 successional stages that included grassland, shrubsteppe, juniper-shrubsteppe, and old-growth juniper woodland in central Oregon. Birds were surveyed monthly from December through April in 1998/1999 and 1999/2000 using the point count method to estimate relative abundance of birds (individuals ? transect –1 year –1 ). We used distance sampling to correct for potential bias in estimating abundance and density among successional stages. A total of 4513 birds (32 species) were detected. Relative abundance of total birds (all species combined) was similar in the juniper-shrubsteppe and old-growth woodland (48.7 and 48.9 individuals ? transect –1 , respectively) but 6 times greater than in the grassland and shrubsteppe (8.0 and 7.7 individuals ? transect –1 , respectively) during the 5-month period. Total density of birds was greater in old-growth juniper woodland and juniper-shrubsteppe than in grassland or shrubsteppe. However, median bird species richness in 1998/1999 was highest in grassland and lowest both in shrubsteppe and juniper-shrubsteppe, and in 1999/2000 it was highest in shrubsteppe and lowest in juniper-shrubsteppe and oldgrowth juniper woodland. American Robins and Townsend's Solitaires were the most abundant species in junipershrubsteppe and old-growth juniper woodland during the winter months. Sage Sparrows and Horned Larks were the most abundant species in shrubsteppe during winter, and Horned Larks were most abundant in grasslands during the early spring transition period prior to nesting. Our results indicate that a different suite of species use these successional stages during the nonbreeding season. If avifauna conservation is a part of long-term management goals, a broad range of successional stages should be maintained on the landscape to provide habitat for a variety of avian species throughout the year.     

Ontogenetic and habitat-related changes in diet of late larval and juvenile suckers (Catostomidae) in Upper Klamath Lake, Oregon

We describe ontogenetic patterns in the diets of shortnose and Lost River suckers (15.8–92.8 mm standard length) from Upper Klamath Lake in summer 1999. Both species made a transition from surface and planktonic prey to benthic prey at about 20–30 mm standard length, corresponding to the approximate size of the juvenile morphological transition. Surface prey was dominated by adult chironomids and undigestable pollen, while benthic prey was dominated by larval chironomids, chydorids, and ostracods. In the 15–20-mm size class, pollen made up >75% of food particles in 68% of specimens, and only 2 specimens in this size class lacked any pollen grains. A better understanding of the prey selection process in larval suckers is needed to determine the importance of this potential source of starvation. The planktonic prey eaten during the surface-to-benthic feeding transition were widely distributed in the lake, suggesting that larvae use emergent vegetation primarily as a refuge from predators. On a numerical basis, crustaceans and larval chironomids contributed most to the diets of larger juveniles. In specimens >40 mm, shortnose suckers ate more Tanytarsini and Lost River suckers ate more chironomid pupae and chydorids. In specimens >40 mm there was a strong habitat-related difference in diet: specimens collected in offshore samples ate more chironomid larvae and pupae, harpacticoid copepods, and chydorids, whereas onshore specimens ate more cyclopoid copepods and invertebrate eggs. The transition from onshore to offshore habitat appears to occur over a broad size range of about 40–90 mm.     

Home range size of Black-backed Woodpeckers in burned forests of southwestern Idaho

We examined home range size of Black-backed Woodpeckers ( Picoides arcticus ) in burned ponderosa pine ( Pinus ponderosa ) / Douglas-fir ( Pseudotsuga menziesii ) forests of southwestern Idaho during 2000 and 2002 (6 and 8 years following fire). Home range size for 4 adult males during the post-fledging period was 115.6–420.9 ha using the 95% fixed-kernel method, and 150.4–766.1 ha using the 100% minimum convex polygon method. Smoothed bootstrap estimates (95%) were 130.0–521.9 ha. Home range sizes were significantly smaller 6 years after fire than 8 years after fire. Each male had from 2 to 8 areas of concentrated use within his home range. We provide recommendations for estimating area requirements of Black-backed Woodpeckers in post-fire ponderosa pine / Douglas-fir forests.     

Waterfowl and shorebird use of surface-mined and livestock water impoundments on the Northern Great Plains

Cluster analysis and stepwise discriminant analysis were used to group waterfowl and shorebird use on water impoundments (bentonite, coal, livestock) on the Northern High Plains. Three bird-use categories—high, medium, and low—were delineated by these analytical procedures. Eleven physical, chemical, and biological parameters of impoundments were related to bird use; water area, nitrogen, and low basin slopes were found to be important parameters in estimating bird use on impoundments. Spring and summer were the best seasons for surveying waterfowl and shorebird water impoundment use.     

Habitat and nesting biology of Mountain Plovers in Wyoming

Although previous research has considered habitat associations and breeding biology of Mountain Plovers in Wyoming at discrete sites, no study has considered these attributes at a statewide scale. We located 55 Mountain Plover nests in 6 counties across Wyoming during 2002 and 2003. Nests occurred in 2 general habitat types: grassland and desert-shrub. Mean estimated hatch date was 26 June ( n = 31) in 2002 and 21 June ( n = 24) in 2003. Mean hatch date was not related to latitude or elevation. Hatch success of nests was inferred in 2003 by the presence of eggshell fragments in the nest scrape. Eggs in 14 of 22 (64%) known-fate nests hatched. All grassland sites and 90% of desert sites were host to ungulate grazers, although prairie dogs were absent at 64% of nest sites. Nest plots had less grass coverage and reduced grass height compared with random plots. More than 50% of nests occurred on elevated plateaus. The Mountain Plover's tendency to nest on arid, elevated plateaus further substantiates claims that the bird is also a disturbed- prairie species.     

Morphology and taxonomy of Klamath Basin suckers (Catostomidae)

We examined morphology of 4 sucker species (Catostomidae) from Klamath and Rogue River basins, Oregon and California. Different pairs of these species have been suspected of hybridizing, and field biologists have experienced difficulty identifying individuals in some areas. The suite of morphological characters used for initial identification was poorly supported by other morphometric characters but well supported by meristic characters, especially when analyses were restricted geographically. In some species sexual dimorphism was evident, with males having longer pectoral fins and females having longer pre-anal counts and measurements. Each species showed geographic differentiation, either between the Lost River subbasin and other Klamath subbasins or between Klamath and Rogue basins. Classification was most difficult for Catostomus snyderi , which was frequently misclassified as all other species, but especially as Chasmistes brevirostris . Despite this, the 2 species are ecologically segregated in the upper subbasins with lake-spawning Ch. brevirostris spatially segregated and river-spawning Ch. brevirostris temporally segregated from river-spawning C. snyderi . We discuss the possibility that a large-headed, thin-lipped species has become extinct in Upper Klamath Lake and alternatively suggest that the form could represent an ecophenotype of Ch. brevirostris that is no longer produced in hypereutrophic Upper Klamath Lake.     

Vegetation complexity and bat‐plant dispersal in Calakmul,Mexico

Fruit production of chiropterochorous plants was studied to test the hypotheses that more complex habitats will harbour: (1) greater plant diversity, (2) higher biomass and density of bat‐dispersed plants, and (3) elevated frugivorous bat abundance. We defined habitat complexity as vegetation structural complexity – the degree of structural arrangement of vegetation. As forested environments are more complex than modified environments, they should harbour more bat‐dispersed species. From 2002 to 2003 in southern Mexico, we observed two fruiting peaks of 56 plant species (20 of which were bat‐dispersed) in tropical subhumid forest, tropical semi‐deciduous forest and modified open areas. Fruit density was greater in the canopy than in the understorey. Phenology alternated across seasons and habitats. Habitat complexity demonstrated no association with bat abundance, fruit mass or fruit density. A positive relationship between fruit mass and frugivorous bat abundance suggests that fruit mass probably influences frugivorous bat movement across time and space.     

A survey of breeding and migratory birds southwest of Farmington, New Mexico

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Abundance variations and life history traits of two sympatric species of Neotropical annual fish (Cyprinodontiformes: Rivulidae) in temporary ponds of southern Brazil

We investigated abundance variations and life history traits (body size, sex ratio, length–weight relationships and condition factor) of two species of annual fish (Austrolebias minuano Costa and Cheffe and Cynopoecilus fulgens Costa) in temporary ponds of southern Brazil. Six samples were taken from small temporary ponds during three annual seasons over 2 years (2008–2009). A total of 104 individuals of A. minuano and 433 individuals of C. fulgens were collected. The abundance of both species tended to decrease from autumn to spring in the 2 years. The overall sex ratio of A. minuano and C. fulgens were 1.0 male to 1.8 females and 1 male to 1.04 females, respectively. Juveniles of both species occurred only in autumn over the two years and no adult was observed during this season. While the length–weight relationship of A. minuano indicated hyperallometric growth, the relationship of C. fulgens indicated values close to isometric growth.     

Comparison of zooplankton community structure between impacted and non-impacted areas of Paranaguá Bay Estuarine Complex,south Brazil

We analysed the seasonal distribution of the zooplankton community in an anthropogenically impacted area (Paranaguá Bay) and a non-impacted area (Laranjeiras Bay) of the Paranaguá Bay Estuarine Complex. Large phytoplankton (> 50 μm) and zooplankton were collected every two months, between August 2003 and June 2004. The phytoplankton community was numerically dominated by diatoms (78%) and dinoflagellates (19%). Zooplankton abundance varied between 670 and 100,716 individuals m^–3, with a dominance of copepods, mainly the calanoids Acartia lilljeborgii, Acartia tonsa and Pseudodiaptomus acutus. A clear seasonal pattern was observed: copepods were significantly more abundant during the rainy than in the dry season. Significant differences in abundance between the two bays were detected only for cirripede larvae, which were more abundant in Paranaguá Bay. This lack of difference between the two areas was probably a consequence of the water circulation along the estuary, which may have diluted and dispersed the pollutants from Paranaguá Bay to other areas of the estuary.