Evaluating a power transmission line in relation to greater sage-grouse populations and other sagebrush-steppe avifauna

Overview

The Nevada Department of Wildlife (NDOW), U. S. Geological Survey (USGS), and Idaho State University (ISU) collaborated on an intensive effort to monitor a population of Greater Sage-Grouse (Centrocercus urophasianus; hereafter sage-grouse) in the northern portion of the Southwest Intertie Project (SWIP) Corridor of Nevada, also known as the ‘One Nevada Transmission Line’ which is being developed by Great Basin Transmission, LLC. This project, spanning over 500 miles, will extend from north Jerome County, Idaho, south to the Harry Allen Substation in Cark County, Nevada. A portion of our study area is scheduled for development of wind energy and associated transmission infrastructure. Sage-grouse within this area may experience substantial alterations in habitat and predator communities following development of wind turbines, transmission lines, facilities, and roads. Regulatory agencies consider potential alterations as threats to sage-grouse population persistence. Personnel from USGS and ISU have initiated a before after control impact (BACI) study design to investigate these threats. The purpose of this study is to collect and interpret empirical data before and after construction of energy infrastructure to understand and mitigate any threats to sage-grouse and other sagebrush endemic vertebrates. This report documents summary data and preliminary findings of 2010, which represent the pre-construction years of the ongoing study. Here, we present information on nest survival, brood survival, and movement of greater sage-grouse during the breeding and summer season. We also summarized and conducted preliminary analysis that identifies vegetation characteristics and environmental factors related to nest and brood site selection and survival. These preliminary findings should be interpreted as only preliminary pre-construction information, as sample sizes were limited.

Pete and Nick Capture Radioed Sage-Grouse

Captured Female Grouse

1. Capture and monitored sage-grouse movement, survivorship, and reproduction following release.
2. Following nest fate, we recorded understory cover at the nest bowl using a coverboard (Jones 1968), Robel pole (Robel 1970), and digital photography
3. Vegetation composition cover at multiple subplots (20 ´ 50 cm) located ≤25 m of each nests using Daubenmire method
4. Multiple a priori generalized mixed effects models with a binomial error distribution at multiple spatial scales will be compared for strength of evidence. We will use an information-theoretic approach, including DAIC, Akaike’s weights, evidence ratios, likelihood-based R², and likelihood ratio tests to evaluate models. Model averaged parameter estimates will be used to develop resource selection functions.
5. Brood-rearing: Monitored successful female grouse with broods
6. Investigated differences in vegetation use between night (roosting) and day (foraging) hours
7. Predator Monitoring: raven, raptor, badger surveys using on foot observation and videography

Tarsus Measurement.

Culmen Measurement.

Preliminary Findings (Pre-Construction of Transmission Lines):

1. 30 female sage-grouse (18 adults and 12 sub-adults) were captured and radio-marked.
2. Estimated nest survival parameter using maximum likelihood was 35.9% (CI 14.8 – 57.7%), using a 37-day period (laying and incubation).
3. Estimated daily survival rate was 97.3% ± 0.9:  11 successful nests and 9 failed nests
4. Successful nests had lesser mean measurements of both vertical vegetation cover (76.0% 4.1) and overall vegetation cover (59.2% 3.6).
5. Unsuccessful nests had a mean vertical vegetation cover of 86.8% 2.2 and overall vegetation cover equaling 66.4% 1.8.
6. Shrub over sage-grouse nests: mean maximum height = 78.2cm ± 7., mean greatest width of nests = 124.3 cm ± 8.2, mean perpendicular width = 97.0 cm ± 8.41, mean litter depth of nests = 3.1 cm ± 0.4.
7. Sage-grouse do select for sagebrush cover in the vicinity of the nest and frequently choose sagebrush for nest placement.
8. Apparent success of broods at the 30-days post-hatch was 70%
9. Our preliminary results suggest that brood-rearing sage-grouse selected areas with ground obstructive cover relative to the available cover
10. We found that sagebrush cover was selected during the day hours (foraging) and during the night (roosting).
11. We detected ravens during 51% of morning surveys, 37% of mid-day surveys and 48% of late-day surveys yielding an overall detection rate of 47% and a total of 136 observed ravens.
12. The number of ravens detected during individual surveys ranged from 0 – 5 birds and the mean number of ravens detected per survey in 2010 was 0.72 birds ± 0.09.