Graduate Thesis Or Dissertation
 

Greater Sage-Grouse (Centrocercus urophasianus) Demographic Rates and Predator Communities in a Degraded Landscape in Modoc County, California

Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6108vk27m

Descriptions

Attribute NameValues
Creator
Abstract
  • The greater sage-grouse (Centrocercus urophasianus: hereafter; sage-grouse) population in Modoc County California is geographically isolated and has been subsidized by translocation to prevent inbreeding depression since 2005. Despite significant efforts to increase the population through translocations and habitat improvement by cutting encroaching western juniper (Juniperus occidentalis), only a single lek remains (from 56 in the 1940s). Since 2017, several large wildfires have occurred on the area that led to an increase in invasive grasses and a decrease in sagebrush (Artemisia sp.) cover that has further degraded important nesting and brooding habitat. In addition to supporting the last known sage-grouse lek, Clear Lake Reservoir is a major stopover point and nesting site for migratory waterfowl and wading birds. This abundance of prey species also attracts a diverse and abundant generalist predator community. I estimated survival for adult females, nests, and chicks and assessed habitat and biotic characteristics that may influence these survival rates to identify factors that may be limiting population growth. I also estimated coyote (Canis latrans) probability of use and avian predator densities to evaluate the predation risk to females, nests and chicks on this study area. I monitored 37 females marked with GPS PTTS, 39 nests, and 8 broods during 3 years (2019-2021). I measured vegetation characteristics for nests at the microsite and landscape scale to evaluate effects on daily nest survival (DNS). I used 70 camera traps to take over 4.9 million photos that I used to estimate coyote probability of use within each season during 2020 and 2021. During these two years I also conducted avian point-count surveys every two weeks at each camera trap location to estimate raven (Corvus corax), and raptor (i.e., hawk (Buteo sp.), harrier (Circus hudsonius), and eagle (Aquila chrysaetos and Haliaeetus leucocephalus)) densities using a distance sampling approach. Nest success across a 29-day incubation period, the maximum number of incubation days at my field site, was 29% (95% CI: 17.1 to 44.8). Chick survival across a 54 day period was 22% (95% CI: 0.9 to 72.3), and female adult survival across a 12 month period was 29% (95% CI: 17.8 to 43.7). At the microhabitat scale, shrub and medusahead cover were the two most supported covariates associated with DNS. Daily nest survival increased as shrub cover increased (β= 3.3; 95% 0.89 to 5.8) but decreased as medusahead cover increased (β= -2.8; 95% CI -5.0 to -0.56). At the landscape scale the log-linear structure of annual grass cover at 400m around the nest had the strongest effect on DNS which increased with increasing grass cover to ~35%, where DNS then stabilized (β = 3.0; 95% CI 0.28 to 5.8). Shrub cover at the landscape scale around nests was 12 % lower than what has been recommended for California and Nevada on the landscape scale, and the amount of annual grasses was 10 % higher than other study sites affected by large wildfires in Oregon, California, and Nevada. My estimated vital rates were 45-55% lower than range-wide estimates. During the course of the sage-grouse breeding season, coyotes used approximately 96 % (95% CI: 0.80 to 0.99) of the camera trap locations and coyote detection probabilities were highest during early brood-rearing for sage-grouse. Raven (Corvus corax) and raptor densities were 0.29 ravens/km2 (95% CI = 0.19 to 0.44) and 0.22 raptors/km2 (95% CI = 0.16 to 0.31), respectively. The overlap of brood-rearing with peak coyote activity could explain decreased brood survival within the first two weeks post-hatch, and why adult predation was the primary cause of brood loss. Ravens and hawks also far outnumber sage-grouse, and the presence of nesting resident predators may be detrimental to this small population of nesting sage-grouse than what might be expected given the estimated density of avian predators. My results suggested recent habitat changes associated with wildfire and the resulting increased distribution of invasive grasses on the study area may have had a detrimental effect on this population across all life stages. The densities and occurrence of predators combined with the reduced availability of vegetation cover used for concealment, and increased perching and nesting structures for avian predators through juniper encroachment, may have increased the risk of sage-grouse females, nests, and chicks to predation.
License
Resource Type
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Rights Statement
Publisher
Peer Reviewed
Language

Relationships

Parents:

This work has no parents.

In Collection:

Items

Thumbnail Title Date Uploaded Visibility Actions
file details SinkChelseaE2023.pdf 2023-02-03 Public Download