2017. Quantifying overlap and fitness consequences of migration strategy with seasonal habitat use and a conservation policy. Ecosphere 8(11):e01991. 10. 1002/ecs2.1991 Abstract. Our study aimed to delineate seasonal habitats and assess differential fitness related to migration strategy and seasonal habitat use of greater sage-grouse (Centrocercus urophasianus, hereafter "sagegrouse"). In addition, we evaluated benefits gained for sage-grouse through the implementation of the Wyoming Core Area Strategy relative to protection of habitat and differences in nest, brood, and annual female survival. We compared the proportion of seasonal habitats that were within or outside Core Areas as delineated with 75% and 95% kernel density contours (KDE). The proportion of summer and winter habitats (95% KDE) that overlapped Core Areas was 0.69 of summer and 0.50 of winter habitat within a Core Area. We found no differences in nest or brood survival among migration strategies or within and outside Core Areas. However, females that did not migrate out of their respective winter habitat had lower risk of death, which highlighted year-round benefits of winter habitat. Females had lower risk of death during winter with the lowest risk occurring during winter in Core Areas. Higher temperature and lower snow water equivalent during the breeding season and fall were detrimental to female survival, whereas neither had an effect on winter survival. Although Core Areas encompassed a large proportion of winter habitat, our results indicate that Core Areas (as delineated) were not the most direct way to protect winter habitat for sage-grouse. During winter, sage-grouse gathered within habitat conducive to winter survival, indicating that disturbances within these winter habitats may have broad consequences for sage-grouse populations.
Fertilization is a common practice, as it improves plant yields. In many areas, biosolids (remains from treated wastewater) are used instead of chemical fertilizers owing to multi-year nutrient release and positive changes in soils and water retention. Little is known about whether biosolids affect animal consumers. Here, we examine diets and nesting sites of American Kestrels (Falco sparverius Linnaeus, 1758) in British Columbia, Canada. Our major study area was a large cattle ranch that has been grazed for over a century and where biosolids were applied in the previous 1–3 years. Kestrels selected nests in areas with higher Northern Flicker (Colaptes auratus (Linnaeus, 1758)) nest density and with a higher proportion of pastures with biosolids applications, but with less forest. Kestrels were observed more often on biosolids-amended pastures than in untreated areas. Kestrels primarily ate voles (genus Microtus Schrank, 1798), but also consumed grasshoppers (Orthoptera) late in the breeding season when grasshoppers were abundant. Kestrel diets were slightly more varied on a nearby control area than on the ranch. Our results suggest that biosolids applications improve prey availability for Kestrels, thus potentially acting as a restoration tool in areas with degraded habitats or where Kestrels have declined.
Degraded grasslands are common worldwide, often due to overgrazing by livestock; such degradation often reduces plant growth and water quality, while increasing soil erosion, wildfires, and invasive species. Recent restoration efforts have used organic amendments to increase soil nutrients, improve water retention, and increase forage production. Biosolids, the stabilised and pathogen-treated remains from wastewater treatment plants, have strong impacts on soil nutrients and plant growth, but there is very little known about impacts on higher trophic levels. We worked on northern grasslands in British Columbia, Canada, to test whether biosolids applications changed grasshopper abundances, body sizes, or species richness. We used hoop transects to measure density and timed net samples to determine richness and evenness. There were significantly higher (~3.8×) grasshopper densities at sites where biosolids were applied 1–2 years before sampling compared with control sites or sites where biosolids were applied in the year of sampling. Tibia lengths of grasshoppers varied with treatment, species, and sex, but there was no clear signature of biosolids leading to bigger body sizes. There were no significant differences in species richness or equitability in relation to the year of the biosolids application. Collectively, our results show that biosolids have large impacts on grasshopper densities, but no clear impact on community structure or body size. Because grasshoppers can be dominant insect herbivores and are critical prey for many birds and mammals, our results suggest biosolids could be an important tool in the context of site restoration or efforts to improve populations of insectivorous vertebrates.
Many food webs are affected by bottom‐up nutrient addition, as additional biomass or productivity at a given trophic level can support more consumers. In turn, when prey are abundant, predators may converge on the same diets rather than partitioning food resources. Here, we examine the diets and habitat use of predatory and omnivorous birds in response to biosolids amendment of northern grasslands used as grazing range for cattle in British Columbia, Canada. From an ecosystem management perspective, we test whether dietary convergence occurred and whether birds preferentially used the pastures with biosolids. Biosolids treatments increased Orthoptera densities and our work occurred during a vole ( Microtus spp .) population peak, so both types of prey were abundant. American Kestrels ( Falco sparverius ) consumed both small mammals and Orthoptera. Short‐eared Owls ( Asio flammeus ) and Long‐eared owls ( Asio otus ) primarily ate voles (>97% of biomass consumed) as did Northern Harriers ( Circus hudsonius, 88% vole biomass). Despite high dietary overlap, these species had minimal spatial overlap, and Short‐eared Owls strongly preferred pastures amended with biosolids. Common Ravens ( Corvus corax ), Black‐billed Magpies ( Pica hudsonia ), and American Crows ( Corvus brachyrhynchos ) consumed Orthoptera, Coleoptera, vegetation, and only a few small mammals; crows avoided pastures with biosolids. Thus, when both insect and mammalian prey were abundant, corvids maintained omnivorous diets, whereas owls and Harriers specialized on voles. Spatial patterns were more complex, as birds were likely responding to prey abundance, vegetation structure, and other birds in this consumer guild.
Hunter harvest of greater sage-grouse (Centrocercus urophasianus; hereafter “sage-grouse”) has been regulated by wildlife agencies during most of the past century. Hunting season regulations were maintained with the intention of providing sustainable hunting opportunities. Sage-grouse populations oscillate over time, and population growth can be influenced by seasonal weather and habitat disturbance. From 1995–2013, we compared sage-grouse lek trends from 22 relatively distinct sage-grouse population segments in 9 western U.S. states and 2 Canadian provinces. We stratified these populations into 3 broad categories (non-hunted [n = 8], continuously hunted [n = 10], and hunting season discontinued between 1996–2003 [n = 4]) with 8 different regulation histories to evaluate the potential impact of harvest on sage-grouse populations. Concomitantly, we assessed the effects of proportion burned, forested and cropland habitat; winter, spring, and summer precipitation; and human population, road, and oil and gas well densities on initial and time-varying lek counts. Density-dependent models fit lek trend data best for all regulation histories. In general, higher proportions of burnt, forested, and cropland habitat; and greater human population and oil and gas well densities were associated with lower equilibrium abundance (K). We found mixed results regarding the effect of hunting regulations on instantaneous growth rate (r). The cessation of harvest from 1996–2001 in approximately half of the largest sage-grouse population in our analysis was associated with higher r. Continuously harvested sage-grouse populations with permit hunting seasons had higher r during years with higher proportion of area exposed to permitted hunting rather than general upland game seasons. However, more liberal hunting regulations were positively associated with higher r in populations continuously harvested under general upland game hunts. Our results suggest that discontinuing harvest in the largest population resulted in greater population growth rates; however, this was not consistently the case for smaller populations. To no surprise, not all sage-grouse populations were influenced by the same environmental change or human disturbance factors. Our results will assist managers to understand factors associated with K, which provides the best targets for conservation efforts.
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