CONTRASTING HABITAT ASSOCIATIONS OF SAGEBRUSH-STEPPE SONGBIRDS IN THE INTERMOUNTAIN WEST.

-I examined the territory size, mating success, nest placement, nest development, and nesting success of the three passerine species restricted to the sagebrush (Artemisia tridentata) habitat in southeastern Idaho. Territories defended by male Sage Thrashers (Oreoscoptes montanus) were larger than those defended by either Sage Sparrows (Amphispiza belli) or Brewer's Sparrows (Spizella breweri). All but one of the territorial Sage Thrashers (n = 19) were successful in securing mates and nesting. Fifty-three percent of the territorial Sage Sparrows (n = 30) and only 23% of the displaying Brewer's Sparrows (n = 30) secured mates and nested. Thrashers nested either on the ground below sagebrush or in the branches of sagebrush plants. Brewer's and Sage sparrows nested only in the shrub canopy of sagebrush. Average incubation and nesting periods (rounded to the nearest whole day) for the Sage Thrasher, Sage Sparrow, and Brewer's Sparrow were 15 (n = 9) and 12 (n = 7) days, 14 (n = 5) and 10 (n = 7) days, and 11 (n = 1) and 9 (n = 1) days respectively. Sage Thrashers (n = 49) and Sage Sparrows (n = 17) had a similar probability of nesting success (0.45 and 0.40, respectively), while the Mayfield success rate for Brewer's Sparrows (n = 7) was only 0.09. Male Sage Sparrows that attracted mates had established larger territories than those that failed to mate. Brewer's Sparrows nested about 10 days later than the other species, which may have resulted in their lower nesting success, since nest site requirements of all species were similar. The Sage Thrasher, Sage Sparrow, and Brewer's Sparrow are common passerine species nesting in the sagebrush-dominated habitat on the Snake River Plain in southeastern Idaho. Each of these is said to be almost completely dependent on the sagebrush environment for survival (Braun et al. 1976). Until recently (Trost et al. 1975, Schroeder and Sturges 1975, Reynolds 1978, Rich 1977, 1978, Reynolds and Rich 1978), the ecology of passerines restricted to this habitat had received limited attention (Bent 1948, Feist 1968, Miller 1968, Paine 1968, Walcheck 1970, and Best 1972). Nesting data have been reported for the thrasher but they are lacking or incomplete for the two sparrows. I present here my findings on the territory size, nest placement, incubation and nesting periods, and the nesting success of these three species. MATERIALS AND METHODS Most of the data were collected from mid-March to mid-July 1976 and 1977, in two 4-ha study areas on the Idaho National Engineering Laboratory (INEL) Site, approximately 48 km west of Idaho Falls, Bonneville Co., Idaho. These areas were about 12 km apart and located in sagebrush steppe habitat (Kiichler 1964) dominated by big sagebrush (Artemisia tridentata; Harniss and West 1973). Data on nest placement and development of nests found elsewhere on the INEL Site were included, but territories were measured only on the two study areas. Reynolds and Rich (1978) presented preliminary data on the nesting ecology of the Sage Thrasher, which were gathered in 1976 on one of these study sites, plus an additional study area 25 km east of the INEL Site. Where appropriate, and unless stated otherwise, data from the present study were combined and presented with theirs in order to increase the sample size for this species. Territories were mapped for displaying males of each species following the methods of Williamson (1964) and Wiens (1973), and territory sizes were calculated according to Reynolds and Rich (1978). I considered males to be territorial only after their territories had been mapped at least three times on successive days. Although territories change in size and shape during the breeding season, the data presented here represent the total area in which territorial displays were recorded for each singing male, and thus represent maximum territory size. Wooden stakes, 1.8-m tall and color-coded with plastic flagging, were placed at 50-m intervals in each study area to ensure accurate mapping of territories and nest sites. Field investigators found nests by observing courtship, nest building, or food carrying behavior, or by flushing a bird from the nest. Birds were flushed by randomly searching the area or by two researchers dragging a 25-m rope with flagging material suspended from it across the top of the vegetation. Nests were examined at 1-3 day intervals. The condition of the nest and the number of eggs and/or nestlings present at each visit were recorded. Hatching for these species was, for the most part, synchronous. Incubation periods were recorded as the time in days elapsed between the date the last egg of a clutch was laid and hatching. Fledging also was generally synchronous, and nesting periods were measured as the number of days between hatching and fledging, recorded for each nest. Nesting success was calculated using the nest-day, egg-day, and nestling-day as units of exposure (Mayfield 1975),

We examined relationships between high-elevation sagebrush (Artemisia spp.) steppe habitats altered by prescribed fire and western juniper (Juniperus occidentalis) encroachment on breeding distributions of Brewer's Sparrows (Spizella breweri), Vesper Sparrows (Pooecetes gramineus), Green-tailed Towhees (Pipilo chlorurus), and Sage Thrashers (Oreoscoptes montanus) on Steens Mountain in southeastern Oregon. In 2000 we conducted fixed-radius point count surveys at 172 sites encompassing burned and unburned sagebrush habitat and a range of juniper densities. For each bird species we developed habitat models using local variables measured in the field and landscape variables derived from remotely sensed data. Akaike's Information Criterion (AICc) was used to select the best-approximating model from a suite of a priori candidate models. Brewer's Sparrows, Sage Thrashers, and Green-tailed Towhees were positively related to increasing local sagebrush cover or percent sagebrush in the landscape, whereas V...

Sagebrush steppe is one of the most threatened ecosystems in North America. Adult density of songbirds within sagebrush steppe is a metric used to evaluate conservation actions. However, relying on only adult density to guide conservation may be misleading. Information on how conservation actions influence the nest density and nest survival of songbird species, in addition to adult density, are needed. We evaluated the relationships between nest density, nest survival, and adult density of Brewer's sparrow (Spizella breweri) and vesper sparrow (Pooecetes gramineus) over 3 breeding seasons in central Montana. Our findings suggest that adult pairs of both species were often present in higher numbers than nests, and this relationship was most prominent for Brewer's sparrows. However, our results do not support density dependence when considering nest survival. This discrepancy suggests that songbirds may not breed every year and that density dependence may be operating on nest densities within these populations differently than we examined. This study provides information on relationships between population demographics for 2 songbird species in grazed sagebrush steppe that will improve monitoring and management activities of conservation efforts.

Shrubsteppe communities are among the most imperiled ecosystems in North America as a result of conversion to agriculture and other anthropogenic changes. In the Intermountain West of the United States, these communities support a unique avifauna, including several species that are declining and numerous others that are of conservation concern. Extensive research in the eastern and central United States and in Scandinavia suggests that fragmentation of formerly continuous forests and grasslands adversely affects reproductive success of birds, yet little is known of the potential effects on avian communities in Western shrublands. I used multi-model inference to evaluate the potential effects of local and landscape variables on nest predation and brood parasitism, and behavioral observations of color-banded birds to evaluate the potential effects of habitat fragmentation on seasonal reproductive success of passerines in the shrubsteppe of eastern Washington State, USA. Reproductive success of shrubsteppe-obligate passerines was lower in landscapes fragmented by agriculture than in continuous shrubsteppe landscapes. Daily survival rates for nests of Brewer's Sparrows (Spizella breweri; n=496) and Sage Thrashers (Oreoscoptes montanus; n=128) were lower in fragmented landscapes, and seasonal reproductive success (percentage of pairs fledging young) of Sage Sparrows (Amphispiza belli; n=146) and Brewer's Sparrows (n=59) was lower in fragmented landscapes. Rates of parasitism by Brown-headed Cowbirds (Molothrus ater) overall were low (4%) but were significantly greater in fragmented landscapes for Brewer's Sparrows, and parasitism resulted in fewer young fledged from successful nests. Simple models of population growth using landscape-specific fecundity and estimates of adult survival derived from return rates of banded male Sage Sparrows and Brewer's Sparrows suggest that fragmented shrubsteppe in Washington may be acting as a population sink for some species. Immediate conservation needs include halting further fragmentation of shrubsteppe, restoring low-productivity agricultural lands and annual grasslands to shrubsteppe where possible, and convincing the public of the intrinsic value of these imperiled ecosystems.

ABSTRACTHuman activity has altered 33–50% of Earth's surface, including temperate grasslands and sagebrush rangelands, resulting in a loss of biodiversity. By promoting habitat for sensitive or wide‐ranging species, less exigent species may be protected in an umbrella effect. The greater sage‐grouse (Centrocercus urophasianus; sage‐grouse) has been proposed as an umbrella for other sagebrush‐obligate species because it has an extensive range that overlaps with many other species, it is sensitive to anthropogenic activity, it requires resources over large landscapes, and its habitat needs are known. The efficacy of the umbrella concept, however, is often assumed and rarely tested. Therefore, we surveyed sage‐grouse pellet occurrence and sagebrush‐associated songbird abundance in northwest Colorado, USA, to determine the amount of habitat overlap between sage‐grouse and 4 songbirds (Brewer's sparrow [Spizella breweri], sage thrasher [Oreoscoptes montanus], sagebrush sparrow [Artemisiospiza nevadensis]), and green‐tailed towhee [Pipilo chlorurus]). During May and June 2013–2015, we conducted standard point count breeding surveys for songbirds and counted sage‐grouse pellets within 300 10‐m radius plots. We modeled songbird abundance and sage‐grouse pellet occurrence with multi‐scaled environmental features, such as sagebrush cover and bare ground. To evaluate sage‐grouse as an umbrella for sagebrush‐associated passerines, we determined the correlation between probability of sage‐grouse pellet occurrence and model‐predicted songbird densities per sampling plot. We then classified the sage‐grouse probability of occurrence as high (probability >0.5) and low (probability ≤0.5) and mapped model‐predicted surfaces for each species in our study area. We determined average songbird density in areas of high and low probability of sage‐grouse occurrence. Sagebrush cover at intermediate scales was an important predictor for all species, and ground cover was important for all species except sage thrashers. Areas with a higher probability of sage‐grouse occurrence also contained higher densities of Brewer's sparrows, green‐tailed towhees, and sage thrashers, but predicted sagebrush sparrow densities were lower in these areas. In northwest Colorado, sage‐grouse may be an effective umbrella for Brewer's sparrows, green‐tailed towhees, and sage thrashers, but sage‐grouse habitat does not appear to capture areas that support high sagebrush sparrow densities. A multi‐species focus may be the best management and conservation strategy for several species of concern, especially those with conflicting habitat requirements. © The Wildlife Society, 2019

Abstract. Invasive plants represent a serious threat to native biodiversity worldwide through direct competition with native species and indirect effects resulting in ecosystem-level changes. In the western U.S., the sagebrush ecosystem has been seriously altered by the invasion of cheatgrass (Bromus tectorum), an exotic annual, and other species including smooth brome (B. inermis), an exotic perennial. We monitored 112 Brewer's Sparrow (Spizella breweri) nests (2006 and 2007) in Grand Teton National Park, Wyoming, to assess the potential effects of a smooth brome vs. native understory on nest survival in sagebrush steppe. Brewer's Sparrows settled earlier and clutch size was larger in native habitat, but indices of nest success were higher in the exotic habitat. Rates of failure and nest predation were higher in the native habitat. Using the logistic-exposure method, we compared estimates of survival in the two habitats. The model with the greatest support, according to AICc model-selection criteria, con...

We examined the influence of local and landscape-level attributes of fragmented habitats in shrubsteppe habitats on the breeding distributions of Sage (Amphispiza belli) and Brewer's (Spizella breweri) Sparrows, Sage Thrashers (Oreoscoptes montanus), Horned Larks (Eremophila alpestris), and Western Meadowlarks (Sturnella neglecta) in the Snake River Plains of southwestern Idaho. We developed habitat (resource) selection models for each species by combining bird counts conducted from 1991 through 1933 with local vegetation characteristics and landscape attributes derived from satellite imagery. Site selection by shrubsteppe species (Sage and Brewer's Sparrows, and Sage Thrashers) depended on local vegetation cover and landscape features, such as the patch size of shrub habitats or the spatial similarity of sites. Marginal sites for these species (with species present in one of three years) were intermediate between unoccupied (never present) and occupied sites along environmental gradients characterized by increasing size of shrub habitat patches and total shrub cover and by decreasing disturbance. Horned Larks and Western Meadowlarks, typical grassland species, were not sensitive to landscape features, and their occupancy depended on the amount of grassland or shrub cover. In contrast to shrubsteppe species, sites that varied by occupancy rates of Western Meadowlarks did not significantly differ in vegetation or landscape components. Our results demonstrate that fragmentation of shrubsteppe significantly influenced the presence of shrub-obligate species. Because of restoration difficulties, the disturbance of semiarid shrubsteppe may cause irreversible loss of habitat and significant long-term consequences for the conservation of shrub-obligate birds. Características del paisaje en ambientes fragmentados de estepas arbustivas y pájaros paserínidos en estado reproductivo.

Estimating species abundance is important for land managers, especially for monitoring conservation efforts. The two main survey methods for estimating avian abundance are point counts and transects. Previous comparisons of these two methods have either been limited to a single species or have not included detection probability. During the 2012 breeding season, we compared and assessed the efficiency (precision for amount of effort) of point count time of detection (PCTD) and dependent double-observer transect (TRMO) methods based on detection probabilities and abundance estimates of five species of songbirds that use a range of habitats in a prairie system in Montana dominated by sagebrush and grassland vegetation. Our focal species included Vesper Sparrows (Pooecetes gramineus), a generalist species found in both shrub and grassland habitat, shrub-obligate Brewer's Sparrows (Spizella breweri), and McCown's Longspurs (Rhynchophanes mccownii), Horned Larks (Eremophila alpestris), and Western Meadowlarks (Sturnella neglecta), three species of grassland obligates that prefer different grass heights. Detection probabilities were significantly higher for TRMO surveys, with less variation for all five species and differences most pronounced for Brewer's Sparrows and Horned Larks. PCTD surveys required less field effort (~8–20 fewer people minutes per plot) than TRMO surveys because the TRMO surveys required two people. However, time spent on TRMO surveys provided between 0.38 and 87 times more precision per people minute than PCTD surveys. Our results suggest that TRMO surveys provide a more efficient (measured as time spent per unit of standard error) field-based technique in sagebrush prairie systems for the species we investigated, resulting in more precise detection and abundance estimates.

Host-parasite interactions increasingly are influenced by human-induced rapid environmental change (HIREC), and the fitness effects of parasitism may be compounded or exacerbated by host traits and/or exposure to additional extrinsic stressors associated with HIREC. Potential interactions between parasitism and different stressors associated with environmental change, however, remain poorly understood for most systems. We examined how parasitism by bird blow flies (Trypocalliphora braueri), ambient weather conditions and habitat disturbance jointly affected offspring traits and juvenile mortality for two declining species of sagebrush songbirds (Brewer's Sparrow, Spizella breweri; and Sage Thrasher, Oreoscoptes montanus) in Wyoming, USA. We evaluated two alternative hypotheses: that parasitism could act (i) in an independent and additive manner with temperature and habitat alteration (Multiple Stressors Hypothesis) or (ii) synergistically to exacerbate the effects of temperature and habitat alteration (Parasitism-HIREC Interaction Hypothesis) on offspring traits and juvenile mortality. We assessed morphometric traits of nestlings and survival of fledglings in relation to parasite loads, temperature and habitat disturbance associated with natural gas development to test these hypotheses. Higher parasite loads and colder temperatures were associated with different effects for nestlings of each host species, reducing tarsus and wing chord length for Brewer's Sparrow and increasing mass for Sage Thrasher. Despite differences in the effect of parasitism on nestling traits, post-fledging mortality risk for both species increased with higher parasite loads. The effects of parasitism and temperature mainly were additive, with limited evidence that weather exacerbated the effects of parasitism. Habitat disturbance had a weak positive effect on nestling tarsus length and post-fledging survival probability for Brewer's Sparrow. Although parasitism rarely results in direct mortality of hosts, parasites can nonetheless exert considerable fitness consequences, especially when combined with extrinsic stressors associated with human-induced environmental changes.

We conducted an experiment in 1989 and 1990 to determine the effects of malathion ultra‐low volume (ULV) aerial spray on reproduction of passerine birds in shrub‐steppe habitat of southern Idaho. The experiment consisted of reducing the insect food base with malathion, a broad‐spectrum insecticide, while monitoring nestling growth variables and daily nest survivorship. Relative arthropod abundance and biomass were reduced on the treatment plot in 1989 and 1990 (F. P. Howe et al., unpublished manuscript). Wing and tarsus lengths of nestling Sage Thrashers (Oreoscoptes montanus) were shorter on the treatment than on the control plot after malathion application in 1989 but not in 1990. Nestling Brewer's Sparrow (Spizella breweri) wing length and mass were lower on the treatment plot in 1990 but not in 1989. Primary length and foot length were unaffected for either species in either year. Multivariate ANOVA indicated that nestling Brewer's Sparrow size (a combination of five growth variables) was smaller on the treatment than on the control site after the 1990 treatment, but similar between sites after the 1989 malathion application. Sage Thrasher nestling size was smaller on the posttreatment malathion plot in 1989, but similar between plots in 1990. The percentage of eggs hatched and percentage of nestlings fledged were unaffected for either species. No differences were detected in Mayfield estimates of nest survivorship for either species in either year. The mean number of Sage Thrashers fledged per nest attempt was lower on the treatment than on the control plot in 1989, but not in 1990. The mean number of Brewer's Sparrows fledged per nest attempt was not affected on the treatment plot. No adult mortality for either species was observed, and nestling mortalities could not be attributed to malathion. Thus, few differences were detected in nestling growth variables and nest survivorship between the control and treatment plots, and these differences were not consistent across years. Under the conditions of this study, malathion had no observable direct effects, and only marginal indirect effects, through food‐base reduction, on Brewer's Sparrow and Sage Thrasher nestling growth and survival.

Oil and natural gas development in the Intermountain West region of North America has expanded over the last 2 decades, primarily within sagebrush dominated landscapes. Although the effects of energy development on high‐profile game species such as the greater sage‐grouse (Centrocercus urophasianus) have been documented, studies examining responses of non‐game birds are lacking. Simultaneously, many songbirds that breed within sagebrush steppe habitats have shown range‐wide population declines that are likely due to widespread habitat loss and alteration. We evaluated songbird abundance and species richness across gradients of oil and natural gas development intensity, as indexed by well density, at 3 energy fields (2 natural gas and 1 oil) in the Upper Green River Basin, Wyoming, USA during 2008–2009. While simultaneously accounting for important habitat attributes, increased well density was associated with significant decreases in Brewer's sparrow (Spizella breweri) and sage sparrow (Amphispiza belli) abundance, particularly in the Jonah natural gas field. Vesper sparrows (Pooecetes gramineus) were also negatively influenced by increased well density. Horned larks (Eremophila alpestris) increased with well density in the Pinedale Anticline natural gas field, and sage thrashers (Oreoscoptes montanus) showed no response to energy development. Species richness was not significantly affected by well density. Results suggest that regional declines of some songbird species, especially sagebrush‐obligates, may be exacerbated by increased energy development. Understanding the specific mechanisms underlying responses to energy development is an important next step and will aid land managers in the development of effective mitigation and management strategies for the maintenance of stable bird communities in sagebrush habitat. © 2011 The Wildlife Society.

Fungal Facilitation in Rangelands: Do Arbuscular Mycorrhizal Fungi Mediate Resilience and Resistance in Sagebrush Steppe?

ABSTRACTNorth American sagebrush (Artemisia spp.)‐obligate birds are experiencing steep population declines due in part to increased disturbance, mainly human‐caused, across their range. At the eastern edge of the sagebrush steppe, this issue may potentially be exacerbated because of natural disturbance by black‐tailed prairie dogs (Cynomys ludovicianus). Our goal was to compare local and landscape models of habitat use by greater sage‐grouse (Centrocercus urophasianus), Brewer's sparrow (Spizella breweri), and sage thrasher (Oreoscoptes montanus) with models including effects of natural (i.e., prairie dog) and anthropogenic disturbance. We used a combination of field data collection, and state and national datasets for the Thunder Basin National Grassland, eastern Wyoming, USA, to understand the factors that influence lek attendance by sage‐grouse and habitat use by 2 passerines in this system. For all 3 species, models including big sagebrush (Artemisia tridentata) cover at local and landscape scales were the most competitive among univariate models, supporting the paradigm that sagebrush is key for these species. Models including anthropogenic disturbance (well density, road density) explained more variation than models of prairie dog disturbance alone for 2 of the 3 species, but long‐term disturbance by prairie dogs did reduce abundance of Brewer's sparrows. Although long‐term prairie dog disturbance has the potential to reduce sagebrush cover for sagebrush‐obligate birds, such events are likely rare because outbreaks of plague (Yersina pestis) and lethal control on borders with private land reduce prairie dog disturbance. Conversely, anthropogenic disturbance is slated to increase in this system, suggesting potentially accelerated declines for sagebrush birds into the future. © 2020 The Wildlife Society.

Defend and Grow the Core for Birds: How a Sagebrush Conservation Strategy Benefits Rangeland Birds

We investigated geographical and temporal variation in clutch size, brood size, and fledging success in three common passerine species in shrubsteppe habitats of the northern Great Basin of western North America. Over a 2-year period we surveyed three vegetationally similar sites spanning a latitudinal gradient of 650 km (the geographical component), one of which we sampled for five consecutive years (the temporal component). Clutch sizes of Sage (Amphispiza belli) and Brewer's (Spizella breweri) sparrows did not differ significantly among sites, but brood sizes and (for Brewer's Sparrow) fledging success did. These geographical differences were associated with site-specific variation in nest-pre- dation rates and were attributed to differences in the abundances of snakes. Nests at a site in central Oregon that lacked snakes suffered virtually no predation during the 2-year geo- graphical sampling, whereas nests in southeastern Washington and northern Nevada suffered significantly higher rates (40% and 93%, respectively). During the 5-year temporal sampling at the central Oregon site, all measured reproductive parameters of Sage and Brewer's sparrows and clutch size in Sage Thrashers (Oreoscoptes montanus) varied significantly. Although the region experienced extremes of precipitation during this period, in Sage Sparrows only brood size was significantly correlated with rainfall during the previous winter. The principal source of variation in Sage Sparrow final repro- ductive success was predation, which peaked during an outbreak of Townsend's ground squirrels (Spermophilus townsendi) in 1979. This ground squirrel irruption appeared to be triggered by a pattern of a drought year followed by two relatively wet years, beginning in winter 1976-1977. Although Brewer's Sparrows also experienced considerable predation pressure in 1979, clutch size, brood size, and fledging success were significantly correlated with winter precipitation. No component of Sage Thrasher reproduction was associated with climatic variation. The relationship between avian reproductive success and precipitation in arid regions is more complex than the traditional view of desert birds responding directly to increased primary and secondary productivity; such relationships are indirectly influenced by the effects of rainfall on predator populations, and are further complicated by time lags (up to 2 years) in predator response.