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Variation in nutrient allocation can influence the timing of breeding and ultimately reproductive output. Time and space constraints might exist, however, if fewer food resources are available to meet the costs of reproduction early during the reproductive season. Here, for the first time, we test whether nutrient‐allocation strategies for reproduction in a shrub‐dependent avian species differ with timing of breeding in different ecoregions: a high‐elevation landscape, containing spatially complex vegetation (Rocky Mountains) vs. a low‐elevation, more homogenous landscape (Great Plains). We analyzed data collected from radio‐telemetry and stable isotopes to assess the degree to which endogenous (body) reserves are used for reproduction and whether variation in allocation strategies was associated with time of year, ecoregion, habitat quality (including sagebrush type and plant greenness), or maternal characteristics. Using a Bayesian statistical framework, we found that females relied on a similar amount of endogenous reserves for reproduction in first nesting and renesting attempts. Additionally, endogenous contributions declined more rapidly throughout the nesting season in the Rocky Mountains than in the Great Plains. Individuals in high‐ and intermediate‐elevation sagebrush types in the Rocky Mountains used similar amounts of endogenous reserves, whereas females nesting in low‐elevation sagebrush used less. Females nesting at intermediate elevations, which experience the greatest flush of new green vegetation during the nesting season, switched their reliance from endogenous‐to‐exogenous sources for reproduction as green vegetation became available during spring. Our study highlights adaptations of a nutrient‐allocation strategy across areas with varying levels of resources in time and space in a habitat specialist bird. Nutrient allocation by individuals residing in high‐elevation areas favors a strategy that mainly uses nutrients gained from wintering habitats, whereas individuals residing in low‐elevation areas mainly use exogenous sources for reproduction.

Many grassland species coevolved with large herbivores and require habitats along the entire structural gradient created by grazing. Widespread declines of grassland birds, however, have prompted concerns about rangeland management. Conceptually, rest-rotation grazing functions as a conservation strategy to mimic historic disturbance regimes and create pasture-level heterogeneity in the absence of fire, but its utility for improving wildlife habitat has not been directly tested, particularly in the mesic mixed-grass prairie. We evaluated rest-rotation grazing as a conservation management technique compared with more traditional grazing systems, including summer rotation and season-long grazing, and assessed effects of different grazing systems and stocking rates on nest site selection and nest survival of sharp-tailed grouse (Tympanuchus phasianellus), an indicator species for grassland ecosystems. Both nest site selection and nest survival were directly related to vertical nesting cover, which was only weakly related to grazing management variables, including grazing system and stocking rate, at moderate stocking rates (≤ 2 animal unit month [AUM] ha− 1). Cattle presence during the nesting period had a positive effect on daily nest survival, potentially through an effect by either the cows or rancher presence on predator behavior. Overall, our results suggest that rest-rotation grazing did not contribute to pasture-level vegetation heterogeneity and that both the selective foraging of cattle and inherent topographic and edaphic variability in our study area may be stronger drivers of heterogeneity at the small spatial scale required by female grouse.

Grassland birds have undergone substantial population declines throughout much of their historic ranges in North America. Most of the remaining grassland bird habitat is restricted to rangelands managed for livestock production, so grazing management has strong implications for grassland bird conservation efforts. We conducted 1 830 point-count surveys at 305 sites during 2016–2017 to evaluate the relative effects of three livestock grazing systems on the abundance and community composition of grassland birds in a northern mixed-grass prairie ecosystem of eastern Montana, United States. Our objectives were to 1) evaluate effects of grazing management on abundance and community composition of grassland obligate birds, focusing specifically on grazing systems, stocking rates, and interactions with rangeland productivity; 2) evaluate the importance of local vegetation characteristics for grassland birds within grazing systems; and 3) assess the effectiveness of rest-rotation grazing to create patch-heterogeneity in rangeland vegetation through the alteration of structural components and the response of grassland birds to these treatments. Overall, we found inconsistent responses in abundances of grassland birds relative to livestock grazing systems and no discernable differences among grazing systems relative to community composition. However, local abundances were often driven by interactions between grazing system and rangeland production potential, suggesting the effects of livestock grazing management were generally mediated by rangeland productivity. In addition, associations between avian abundance and grazing management parameters (e.g., stocking rate) were species specific. Ubiquitous guidelines for livestock grazing systems may be inappropriate for grassland bird conservation efforts in the northern mixed-grass prairie, and high stocking rates may negatively impact populations of dense-grass obligate grassland birds in this region.

Mechanisms underlying habitat use in most species are poorly understood. Therefore, we integrated behavioral and forest cover type data to test hypotheses underlying the choice of two key cover types used by male Ruffed Grouse (Bonasa umbellus) in northern Minnesota, USA. Forests of aspen (Populus spp.) are the presumptive highest quality cover type for Ruffed Grouse because this bird species achieves its highest breeding densities in this cover type. Yet, males select cover types of conifer even when nearby cover types of aspen remain vacant. We examined this conundrum – selection of inferior cover types when presumed better types are available – by randomly selecting 23 male Ruffed Grouse from among a contiguous population of territorial males and used automated video systems to monitor their breeding display behavior. We predicted that if conifer cover types were indeed inferior habitat for Ruffed Grouse, males that established territories in these cover types would either drum (auditory displ...

Habitat selection links individual behavior to population abundance and dynamics, so evaluation of habitat selection is necessary for conservation and management. Land management can potentially alter both the structure and composition of habitats, thus influencing habitat selection and population size. Livestock grazing is the dominant land use worldwide and, while overstocking has been linked to the decline of many wildlife species, properly managed grazing could improve habitat quality and maintain native rangeland habitats. We evaluated breeding season habitat selection of female sharp-tailed grouse, an indicator species for grassland ecosystems, in relation to grazing management and landscape features in eastern Montana and western North Dakota. At broad spatial scales, females selected for multiple landscape features, including grassland, but exhibited no selection for either landscape or management variables when selecting habitat at smaller spatial scales. Females selected for pastures managed with rest-rotation grazing when choosing a home range, but selection did not equate to improved fitness. Moreover, we observed strong individual variation in both home range size and third-order habitat selection. While the high variability among individuals makes specific management recommendations difficult, selection for grassland habitats at broad scales suggests that strategies that maintain intact native rangelands are important for the conservation of sharp-tailed grouse.

Much interest lies in the identification of manageable habitat variables that affect key vital rates for species of concern. For ground‐nesting birds, vegetation surrounding the nest may play an important role in mediating nest success by providing concealment from predators. Height of grasses surrounding the nest is thought to be a driver of nest survival in greater sage‐grouse (Centrocercus urophasianus; sage‐grouse), a species that has experienced widespread population declines throughout their range. However, a growing body of the literature has found that widely used field methods can produce misleading inference on the relationship between grass height and nest success. Specifically, it has been demonstrated that measuring concealment following nest fate (failure or hatch) introduces a temporal bias whereby successful nests are measured later in the season, on average, than failed nests. This sampling bias can produce inference suggesting a positive effect of grass height on nest survival, though the relationship arises due to the confounding effect of plant phenology, not an effect on predation risk. To test the generality of this finding for sage‐grouse, we reanalyzed existing datasets comprising >800 sage‐grouse nests from three independent studies across the range where there was a positive relationship found between grass height and nest survival, including two using methods now known to be biased. Correcting for phenology produced equivocal relationships between grass height and sage‐grouse nest survival. Viewed in total, evidence for a ubiquitous biological effect of grass height on sage‐grouse nest success across time and space is lacking. In light of these findings, a reevaluation of land management guidelines emphasizing specific grass height targets to promote nest success may be merited.

Six years of point count data in eastern Nebraska and western Iowa, USA, were used to investigate how the community structure of grassland birds and the densities of four focal species (common yellowthroat, dickcissel, grasshopper sparrow and sedge wren) varied on conservation lands with differing management strategies (i.e., warm- versus cool-season grasses and low- to high-diversity plantings), and between conservation and unmanaged marginal grasslands (e.g., field borders and terraces). Model-selection results indicated that grasshopper sparrow and dickcissel densities were influenced by grassland type, with higher densities in parcels dominated by warm-season grasses. Species-specific changes in density in response to planting diversity reinforced the value of creating heterogeneous habitat for grassland birds. Densities for all four species were substantially lower in unmanaged marginal grasslands versus conservation parcels and the community structure between the two habitats differed significantly, with generalist species (e.g., American robins, common grackles and grassland species associated with shorter, sparse and patchy vegetation (e.g., horned lark and vesper sparrow)) largely replacing tallgrass specialists in unmanaged marginal grassland parcels.

When land managers incorporate the habitat needs of grassland birds into their planning, they typically rely on management recommendations based on habitat use by adults during nesting. Habitat requirements for other critical life stages are seldom known and may differ from those of nesting adults. Using radio-telemetry, we examined survival and habitat use by juvenile Dickcissels (Spiza americana) during the postfledging period. In 2003 and 2004, we monitored 60 fledgling Dickcissels for ≤30 days after they left the nest. Mortality rates were highest during the first week after leaving the nest, and only 33% of the fledglings survived the first four weeks after leaving the nest. Estimated mean survival times were 16.9 ± 1.6 days after birds left the nest. In both years, fledgling survival was positively associated with dense vertical and horizontal structure of forbs at nests. Survival tended to be positively associated with vertical grass density on adult territories and negatively associated with patchily distributed forbs on adult territories. Fledgling habitat use was restricted to areas where Dickcissels nested and adjacent fields. Habitats used included corn and soybean fields, grasslands, and wetlands. Our results suggest that the fledgling period is a critical stage for Dickcissels and that fledglings require habitat similar to habitat used for nesting. Supervivencia Durante el Período Posterior al Emplumamiento en Spiza americana: Implicancias para el Manejo de Hábitat y Conservación

L-Cysteine-glutathione disulfide, a ubiquitous substance present in mammalian cells, was shown to be highly effective in protecting mice against acetaminophen-induced hepatotoxicity. Since the corresponding D-cysteine-glutathione disulfide was totally ineffective in this regard, an enzymatic mechanism that provides glutathione directly to cells is postulated.

A series of double-prodrugs of L-cysteine, designed to release L-cysteine in vivo and stimulate the biosynthesis of glutathione (GSH), were synthesized. To evaluate the hepatoprotective effectiveness of these double-prodrugs, male Swiss-Webster mice were administered acetaminophen (ACP) (2.45 mmol/kg (360 mg/kg), intraperitoneally (i.p.)). Prodrug (2.50 mmol/kg, i.p. or 1.25 mmol/kg, i.p., depending on the protocol) was administered 1 h before ACP as a priming dose. A supplementary dose of prodrug (2.5 mmol/kg, i.p. or 1.25 mmol/kg, i.p. depending on the protocol) was administered 0.5 h after ACP. The plasma alanine amino transferase (ALT) values, 24 h after ACP administration were transformed to logs and the 95% and 99% confidence intervals of the log values were plotted and compared for each group. Hepatoprotection was assessed by the degree of attenuation of plasma ALT levels. With these multiple dose schedules, the use of 2% carboxymethylcellulose as vehicle for the prodrugs was found to be detrimental; therefore, the prodrugs were dissolved in dilute aqueous base and the pH adjusted for administration. When a priming dose was given 1 h before ACP followed by a supplementary dose 0.5 h after ACP, only N,S-bis-acetyl-L-cysteine, where both the sulfhydryl and amino groups of L-cysteine were functionalized with the acetyl group, was found to be effective in protecting mice against the hepatotoxic effects of ACP. This suggests that these acetyl groups were rapidly hydrolyzed in vivo to liberate L-cysteine. In contrast, N-acetylation of 2(R,S)-methylthiazolidine-4(R)-carboxylic acid (MTCA) and its 2-n-propyl analog (PTCA), or N-acetylation of 2-oxothiazolidine-4-carboxylic acid (OTCA), reduced the hepatoprotective effects relative to the parent MTCA, PTCA, and OTCA, indicating that the release of L-cysteine in vivo from these N-acetylated thiazolidine prodrugs was metabolically unfavorable. The carbethoxy group, whether functionalized on the sulfhydryl or on the amino group of L-cysteine, or on the secondary amino group of MTCA, appears to be a poor "pro-moiety," since these carbethoxylated double-prodrugs of L-cysteine did not protect mice from ACP-induced hepatotoxicity.