Columbian sharp-tailed grouse nesting ecology: wind energy and habitat

The rapid pace of wind-energy development has increased stakeholder concerns regarding the potential effects on wildlife. Locations targeted for wind-energy development frequently overlap prairie grouse and greater sage-grouse (Centrocercus urophasianus) habitats. Research suggests that anthropogenic developments may have negative effects on these species. There is, however, no information published regarding the effect of wind-energy development on Columbian sharp-tailed grouse (Tympanuchus phasianellus columbianus), a subspecies that has twice been petitioned for Endangered Species Act protection. To address this need, from 2014 to 2015 we studied Columbian sharp-tailed grouse nesting ecology across restored grasslands in eastern Idaho, USA, where a 215-turbine wind-energy complex had been developed. We monitored 147 nests from 135 females captured at leks 0.1–13.8 km from wind turbines. We used an information-theoretic approach to evaluate the influence of wind-energy infrastructure and habitat characteristics on nest-site selection and daily nest survival. We did not detect any influence of wind-energy infrastructure on nest-site selection or nest survival. Nest-site selection and daily nest survival were influenced by vegetation structure and composition measured at 2 spatial scales. Females selected nest sites with more restored grassland containing >30% forb cover within the nesting core-use area (i.e., 60 ha around the nest) and exhibited a functional response to the availability of that land cover type. Daily nest survival was best predicted by visual obstruction at the nest site and the amount of restored grassland containing >30% forb cover within the nesting core-use area. We recommend wildlife managers continue to implement management practices that will provide bunchgrass-dominated grasslands with >30% forb cover in restored grasslands (e.g., Conservation Reserve Program fields) within Columbian sharp-tailed grouse range. © The Wildlife Society, 2019     

Recency, range expansion, and unsorted lineages: implications for interpreting neutral genetic variation in the sharp-tailed grouse (Tympanuchus phasianellus)

Both current and historical patterns of variation are relevant to understanding and managing ecological diversity. Recently derived species present a challenge to the reconstruction of historical patterns because neutral molecular data for these taxa are more likely to exhibit effects of recent and ongoing demographic processes. We studied geographical patterns of neutral molecular variation in a species thought to be of relatively recent origin, Tympanuchus phasianellus (sharp-tailed grouse), using mitochondrial control region sequences (CR-I), amplified fragment length polymorphisms (AFLP), and microsatellites. For historical context, we also analysed CR-I in all species of Tympanuchus. Within T. phasianellus, we found evidence for restricted gene flow between eastern and western portions of the species range, generally corresponding with the range boundary of T. p. columbianus and T. p. jamesi. The mismatch distribution and molecular clock estimates from the CR-I data suggested that all Tympanuchus underwent a range expansion prior to sorting of mitotypes among the species, and that sorting may have been delayed as a result of mutation-drift disequilibrium. This study illustrates the challenge of using genetic data to detect historical divergence in groups that are of relatively recent origin, or that have a history dominated by nonequilibrium conditions. We suggest that in such cases, morphological, ecological, and behavioural data may be particularly important adjuncts to molecular data for the recognition of historically or adaptively divergent groups.     

Testing the reproductive and somatic trade‐off in female Columbian ground squirrels

Energetic trade‐offs in resource allocation form the basis of life‐history theory, which predicts that reproductive allocation in a given season should negatively affect future reproduction or individual survival. We examined how allocation of resources differed between successful and unsuccessful breeding female Columbian ground squirrels to discern any effects of resource allocation on reproductive and somatic efforts. We compared the survival rates, subsequent reprodction, and mass gain of successful breeders (females that successfully weaned young) and unsuccessful breeders (females that failed to give birth or wean young) and investigated “carryover” effects to the next year. Starting capital was an important factor influencing whether successful reproduction was initiated or not, as females with the lowest spring emergence masses did not give birth to a litter in that year. Females that were successful and unsuccessful at breeding in one year, however, were equally likely to be successful breeders in the next year and at very similar litter sizes. Although successful and unsuccessful breeding females showed no difference in over winter survival, females that failed to wean a litter gained additional mass during the season when they failed. The next year, those females had increased energy “capital” in the spring, leading to larger litter sizes. Columbian ground squirrels appear to act as income breeders that also rely on stored capital to increase their propensity for future reproduction. Failed breeders in one year “prepare” for future reproduction by accumulating additional mass, which is “carried over” to the subsequent reproductive season.     

Western Snowy Plovers Charadrius alexandrinus nivosus select nesting substrates that enhance egg crypsis and improve nest survival

Predation is an important cause of nest failure for many birds and has shaped the life‐history characteristics of many species, especially ground‐nesting shorebirds. We examined nesting success, causes of clutch failure and nest survival in relation to variation in substrate characteristics in a colour‐marked population of Western Snowy Plovers Charadrius alexandrinus nivosus breeding on riverine gravel bars in coastal northern California. Plovers experienced higher nesting success on gravel bars than on nearby beaches, which were characterized by more homogeneous, sandy substrates. On gravel bars, Plovers nested in habitats characterized by large, heterogeneous substrates, with more egg‐sized stones, compared with random sites. Egg crypsis, as indexed by time required of a naïve observer to detect a nest, increased with number of egg‐sized substrates. Nest survival correlated negatively with heterogeneity of substrates and positively with the number of egg‐sized stones. Consistently high nesting success of Plovers on gravel bars indicates that this high‐quality habitat deserves special management considerations given the species’ threatened status.     

Bayesian hierarchical model assessment of nest site and landscape effects on nest survival of aplomado falcons

We investigated potential effects of nest site and landscape scale factors, including anthropogenic disturbance and habitat patchiness, on the nesting success of a reintroduced population of northern aplomado falcons (Falco femoralis septentrionalis) in southern Texas. We monitored 62 nesting attempts during 2002–2004 in the Lower Rio Grande Valley. We developed hierarchical models describing daily nest survival rates (DSR) and compared the models using a Bayesian approach in R and WinBUGS. We considered possible effects of nest age, temporal trends, nest site variables, landscape structure, territory (a random effect), and 3 measures of anthropogenic disturbance: distance to paved road, proximity to power pole, and nocturnal light intensity. Whether evaluated by Deviance Information Criterion (DIC) scores or the models' overall posterior probabilities as estimated with a reversible jump Markov Chain Monte Carlo algorithm, none of our landscape or disturbance measures affected DSR. Rather, variation in DSR was best described by nest height, overhead cover, and nest source (artificial or natural). These nest site level factors may be manipulated by managers through provision of artificial nests. We recommend that artificial nests continue to be provided, as such nests are highly successful when located on moderately tall substrates, and they permit researchers to access nest contents for population monitoring. © 2011 The Wildlife Society.     

Effects of fire and grazing on grasshopper sparrow nest survival

Patch-burn grazing is a management framework designed to promote heterogeneity in grasslands, creating more diverse grassland structure to accommodate the habitat requirements of many grassland species, particularly grassland birds. Published studies on the effects of patch-burn grazing on passerines have been conducted on relatively large (430–980 ha pastures), contiguous grasslands, and only 1 of these studies has investigated the reproductive success of grassland birds. We assessed the effects of the patch-burn grazing and a more traditional treatment on the nesting ecology of grasshopper sparrows (Ammodramus savannarum) in small (<37 ha pastures) grasslands located in southern Iowa from May to August of 2008 and 2009. The study pastures were grazed from May to September and prescribed burns were conducted in the spring. We investigated the effects of treatments on clutch size and modeled grasshopper sparrow nest survival as a function of multiple biological and ecological factors. We found no difference in clutch size between treatments; however, we did find a reduction in clutch size for nests that were parasitized by brown-headed cowbirds (Molothrus ater). Constant daily survival rates were greater in patch-burn grazed pastures than in grazed-and-burned pastures (patch-burn grazed rate and grazed-and-burned rate ). Competitive survival models included year, stage of nest, nest age, and cool-season grass (csg) abundance within 5 m of the nest. Overall, csg abundance had the greatest effect on survival and had a negative influence. Although survival rates were highest in patch-burn grazed pastures, multiple factors influenced grasshopper sparrow survival. Nest survival rates for both treatments were relatively low, and variables other than treatment were more instrumental in predicting grasshopper sparrow survival. We recommend decreasing overall vegetation cover if increasing nesting habitat for grasshopper sparrows is a management goal. In addition, we recommend further investigation of heterogeneity management in fragmented landscapes to better understand how it affects biodiversity in relatively small management units that typify grassland habitats in the Midwest. © 2011 The Wildlife Society.     

Senescence and age-specific trade-offs between reproduction and survival in female Asian elephants

Although studies on laboratory species and natural populations of vertebrates have shown reproduction to impair later performance, little is known of the age-specific associations between reproduction and survival, and how such findings apply to the ageing of large, long-lived species. Herein we develop a framework to examine population-level patterns of reproduction and survival across lifespan in long-lived organisms, and decompose those changes into individual-level effects, and the effects of age-specific trade-offs between fitness components. We apply this to an extensive longitudinal dataset on female semi-captive Asian timber elephants (Elephas maximus) and report the first evidence of age-specific fitness declines that are driven by age-specific associations between fitness components in a long-lived mammal. Associations between reproduction and survival are positive in early life, but negative in later life with up to 71% of later-life survival declines associated with investing in the production of offspring within this population of this critically endangered species.     

Snowy plover nest survival in Kansas and effective management to counter negative effects of precipitation

Snowy plovers (Charadrius nivosus) are a species of conservation concern throughout North America and listed as a threatened species in Kansas. Management to minimize the effects of flooding and predation were implemented at Kansas breeding sites in the 1980s to encourage reproductive success. However, the effectiveness of those strategies and the effect of other variables that may influence nest survival have not been formally assessed. We used Program MARK to model the daily survival rate (DSR) of 317 snowy plover nests with 14 habitat- and management-related covariates to identify factors that influence nest survival and examine the efficacy of current management practices. In 2005 and 2006, we monitored nests and collected habitat data at the 2 known breeding sites in Kansas, Quivira National Wildlife Refuge (NWR) and Cheyenne Bottoms Wildlife Area (WA). Overall DSR was greater at Quivira NWR in 2006 (0.954) than at Cheyenne Bottoms WA (0.917) and Quivira NWR (0.942) in 2005. We developed 88 candidate models of which 4 competing models (ΔAIC_c < 2) were identified. We selected the most parsimonious model (K = 14, w_i = 0.23) as the remaining 3 included covariates deemed biologically uninformative. This model included the effect of study site and year on a quadratic time trend, and included covariates quantifying nest age; precipitation; the proportion of gravel, rock, and vegetation at nests; occurrence within an electric fence and within 20 m of a road; occurrence on a human-constructed nest mound; and adult capture during incubation. We found a strong positive relationship between the use of nest mounds and DSR, and a strong negative relationship between precipitation and DSR. We also found a strong positive relationship between DSR and the proportion of vegetation at nest sites, the occurrence of a nest within an electric fence, and adult capture at a nest. We noted a strong negative relationship between DSR and occurrence within 20 m of a road. However, we found that DSR was not sensitive to the proportion of vegetation at a nest, occurrence within an electric fence or within 20 m of a road, and to adult capture at a nest in light of covariates quantifying precipitation and the use of nest mounds. We found weak support for a positive relationship between DSR, nest age, and the proportion of gravel and rock at nests. Our results indicate that large rainfall events are a major source of snowy plover nest loss in Kansas that can be mitigated by the construction of nest mounds. Limited influence of environmental variables found to influence nest survival at other breeding sites suggests that threats to snowy plover nest survival are site specific and managers should assess local sources of nest loss prior to implementing management strategies to improve reproductive success. © 2012 The Wildlife Society.     

Wood thrush nest success and post-fledging survival across a temporal pulse of small mammal abundance in an oak forest

1. Synchronized mass production of seed crops, such as acorns, produces a resource pulse that may have far-reaching consequences for songbird populations through its effects on avian predators. Seed production in these forests represents only the first of several pulsed events. Secondary pulses emerge as mast-consuming rodents numerically respond to seed production and tertiary pulses emerge as generalist predators, such as raptors, numerically respond to rodents. In turn, these two groups reduce nest productivity and juvenile survivorship 1 and 2 years, respectively, after the initial pulse in seed production. 2. At our study site in south-eastern New York, USA, autumn acorn abundance (primary pulse) largely determines rodent abundance (secondary pulse) the following spring. We tested the hypotheses that the population dynamics of a shrub-nesting passerine (wood thrush Hylocichla mustelina), is influenced by rodents through the: (a) direct effect of predation by rodents; (b) indirect effect of rodents on the abundance of raptors (tertiary pulse); and (c) indirect effect of rodent abundance on raptor diet. The latter specifically hypothesizes that a crash in the rodent population in the wake of region-wide failure of acorn production leads to an extreme diet shift in raptors that increases post-fledging mortality in birds. 3. We conducted a 3-year study to examine variation in wood thrush nest success and fledgling survival, using radio telemetry, across a pulse of rodent abundance (i.e. low, medium and high). We also updated and reanalysed regional wood thrush population growth rates as a function of the annual variation in rodent abundance. 4. Fledgling survivorship, but not nest success, varied in relation to annual rodent abundance. Raptors and eastern chipmunks Tamias striatus were the most commonly identified predators on fledglings. Fledgling survivorship was greatest at intermediate rodent abundance consistent with a shift in raptor diet. Regional rate of wood thrush population growth showed a unimodal relationship with rodent abundance, peaking during years with intermediate rodent abundance. This unimodal pattern was due to wood thrush population growth rates near or below zero during rodent population crashes. 5. The telemetry study, pattern of regional abundance and synchronized population dynamics of coexisting thrushes suggest a common mechanism of behavioural changes in raptors in response to declines in rodent prey, which in turn affects thrush population dynamics.     

Habitat suitability and nest survival of white-headed woodpeckers in unburned forests of Oregon

We evaluated habitat suitability and nest survival of breeding white-headed woodpeckers (Picoides albolarvatus) in unburned forests of central Oregon, USA. Daily nest-survival rate was positively related to maximum daily temperature during the nest interval and to density of large-diameter trees surrounding the nest tree. We developed a niche-based habitat suitability model (partitioned Mahalanobis distance) for nesting white-headed woodpeckers using remotely sensed data. Along with low elevation, high density of large trees, and low slope, our habitat suitability model suggested that interspersion–juxtaposition of low- and high-canopy cover ponderosa pine (Pinus ponderosa) patches was important for nest-site suitability. Cross-validation suggested the model performed adequately for management planning at a scale >1 ha. Evaluation of mapped habitat suitability index (HSI) suggested that the maximum predictive gain (HSI = 0.36), where the number of nest locations are maximized in the smallest proportion of the modeled landscape, provided an objective initial threshold for identification of suitable habitat. However, managers can choose the threshold HSI most appropriate for their purposes (e.g., locating regions of low–moderate suitability that have potential for habitat restoration). Consequently, our habitat suitability model may be useful for managing dry coniferous forests for white-headed woodpeckers in central Oregon; however, model validation is necessary before our model could be applied to other locations. © 2011 The Wildlife Society.