Geology topics

Skyler T. Vold

Publications and source records attributed to Skyler T. Vold.

4 recordsLinked to original sources

USGS2026

Range-wide population trend analysis for greater sage-grouse ( Centrocercus urophasianus )—Updated 1960–2025

Greater sage-grouse ( Centrocercus urophasianus ; hereafter sage-grouse) are at the center of State and national land-use policies largely because of their unique life-history traits as an ecological indicator for the health of sagebrush ecosystems. This updated population analysis provides State and Federal land and wildlife managers with the best available science to help guide management and conservation plans aimed at benefitting sage-grouse populations and the ecosystems they inhabit. This analysis relied on previously published population modeling methodology from Coates and others (2021, 2022a) and incorporates population lek count data for 1960–2025. Included in this report are methodological updates to period terminology, expanded reporting of trends across all nadir-to-nadir combinations, and revised extirpation probability estimation that utilizes every historic population nadir to forecast abundance. Each of these updates are detailed under individual Modification sections. Additional updates include simulation analyses that evaluate the effects of progressively longer exclusions of Wyoming lek count data (Wyoming Game and Fish Department has not provided access to a complete lek count data set since 2023) on trends, extirpation probabilities, and targeted annual warning system signals. State-space models estimated a 2.7-percent average annual decline in sage-grouse populations between 1966 and 2021 (Period 1–7, six population oscillations) across their geographical range. The average annual decline among climate clusters for the same number of oscillations ranged between 2.0 and 3.5 percent. Cumulative declines were 42.4, 61.7, and 77.9 percent range-wide in Period 5–7 (19 years [two oscillations]), Period 3–7 (36 years [four oscillations]), and Period 1–7 (55 years), respectively. Between 2024 and 2025 (1-year, non-trend timeframe), range-wide population size declined 1.9 percent ( 95-percent credible interval [CRI]= −4.71–1.48). Simulations of missing data from Wyoming showed that progressively longer gaps produced more negative trend estimates and higher extirpation probabilities, predominantly within Wyoming. Effects on targeted annual warning system signals were more nuanced, with missed warnings occurring inside and outside Wyoming and false warnings occurring predominantly within Wyoming.

California, Colorado, Idaho, Montana, Nevada, Nort↗

USGS2026

Estimating greater sage-grouse population sizes within Oregon, 2017–24

We fit a binomial mixture ( N -mixture) model to lek (breeding area) count data to estimate annual population sizes of greater sage-grouse ( Centrocercus urophasianus ; sage-grouse) within Oregon between 2017 and 2024. Population estimates were delineated among 24 priority areas for conservation, and additional sources of information were considered, including male-to-female sex ratios, lek attendance rates, numbers of unmodeled leks, and the existence of unsampled/unknown leks. In 2024, Oregon was estimated to contain approximately 41,875 sage-grouse (95-percent credible interval [CRI=38,980–54,634]), which was down from a high of 50,869 (95-percent CRI=41,794–66,238) in 2017. A nadir (low point) was identified during 2019, when the median statewide population estimate was 30,644 birds. A complete population oscillation was not evident during the inferential period based on local maxima that were observed during the start (2017) and stop (2024) years of analysis. In addition to estimating population sizes, we evaluated N -mixture model estimates for precision and accuracy after randomly removing single and repeat counts in 10-percent increments (relative to total sample size). We estimated an increase in absolute bias of approximately 1.6 percent for every 10-percent reduction in effort.

Oregon↗

USGS2026

Estimating greater sage-grouse population sizes within the state of Oregon, USA 2017–2024

We fit an N -mixture model to lek (breeding area) count data to estimate annual population sizes of greater sage-grouse ( Centrocercus urophasianus ; sage-grouse) within the state of Oregon, USA between 2017–2024. Population estimates were delineated among 24 Priority Areas for Conservation (PACs) and considered additional sources of information including male-to-female sex ratios, lek attendance rates, numbers of unmodeled leks, and the existence of unsampled/unknown leks. In 2024, the state of Oregon was estimated to contain approximately 41,875 sage-grouse (95% credible interval [CRI] = 38,980–54,634), which was down from a high of 50,869 (95% CRI = 41,794–66,238) in 2017. A nadir (low point) was identified during 2019, when the median statewide population estimate was 30,644 birds. A complete population oscillation was not evident during the inferential period based on local maxima that were observed during the start (2017) and stop (2024) years of analysis. In addition to estimating population sizes, we evaluated N -mixture model estimates for precision and accuracy after randomly removing single and repeat counts in 10% increments (relative to total sample size). We estimated an increase in absolute bias of approximately 1.6% for every 10% reduction in effort.

BioRxiv↗

USGS2017

Comparison of acoustic recorders and field observers for monitoring tundra bird communities

Acoustic recorders can be useful for studying bird populations but their efficiency and accuracy should be assessed in pertinent ecological settings before use. We investigated the utility of an acoustic recorder for monitoring abundance of tundra‐breeding birds relative to point‐count surveys in northwestern Alaska, USA, during 2014. Our objectives were to 1) compare numbers of birds and species detected by a field observer with those detected simultaneously by an acoustic recorder; 2) evaluate how detection probabilities for the observer and acoustic recorder varied with distance of birds from the survey point; and 3) evaluate whether avian guild‐specific detection rates differed between field observers and acoustic recorders relative to habitat. Compared with the observer, the acoustic recorder detected fewer species (β Method = −0.39 ± 0.07) and fewer individuals (β Method = −0.56 ± 0.05) in total and for 6 avian guilds. Discrepancies were attributed primarily to differences in effective area surveyed (91% missed by device were >100 m), but also to nonvocal birds being missed by the recorder (55% missed <100 m were silent). The observer missed a few individuals and one species detected by the device. Models indicated that relative abundance of various avian guilds was associated primarily with maximum shrub height and less so with shrub cover and visual obstruction. The absence of a significant interaction between survey method (observer vs . acoustic recorder) and any habitat characteristic suggests that traditional point counts and acoustic recorders would yield similar inferences about ecological relationships in tundra ecosystems. Pairing of the 2 methods could increase survey efficiency and allow for validation and archival of survey results.

Alaska↗