Jared Baxter and Dr. Randy Larsen, Plant and Wildlife Science
Greater Sage-‐Grouse are a sagebrush-‐obligate species of national concern. In 2010, US Fish and Wildlife Service determined Greater Sage-‐Grouse warranted protection under the Endangered Species Act (1973) but were precluded due to higher priority species. Low chick and juvenile recruitment have been suggested as factors influencing this decline (Beck et al. 2006, Taylor et al. 2012). Consequently, obtaining chick survival estimates that are as accurate as possible is essential to better understanding this important part of their life history and for the conservation of the species.
Methods used for estimating Greater Sage-‐Grouse chick survival have changed over time, with each method having advantages and disadvantages. Methods such as walking through sagebrush flushing broods, using a dog to locate chicks or spotlighting chicks at night can be time intensive and often result in imperfect detection. With recent technological advances, researchers have attached micro-‐ transmitters to chicks and then determined chick fate by locating the chicks using radio-‐telemetry. While this method allows researchers to more accurately estimate chick survival, it is very intrusive and may reduce chick survival (Baxter et al. 2013a).
Lukacs’ model, Young Survival from Marked Adults in program MARK, is a new method for estimating chick survival. The method was developed by Lukacs et al. (2004) using Mountain Plovers in Colorado. The advantages of this method are 1) it only requires flushing the marked hen and then observing the number of chicks (this being less intrusive than using micro-‐transmitters), and 2) it allows for imperfect detection of chicks. The objective of our research was to estimate Greater Sage-‐Grouse chik survival in Strawberry Valley, Utah using 14 years of data from 1998-‐2012, excluding 2002.
The Strawberry Valley study area measures about 24,200 ha and is located in Wasatch County, Utah. The valley is characterized as montane sagebrush steppe with elevations ranging from 2280 to 2440 m. Mountain big sagebrush is the principal shrub in the valley. Strawberry Reservoir is the dominant feature in the valley consisting of up to 6950 surface ha of water ( apprx. 29% of the study area) that has decreased and fragmented sagebrush habitat.
We captured ≥ 1 hen each year from March-‐May 1998-‐2012, except 2002. We then placed a 22 g necklace radio-‐transmitter (Advanced Telemetry Systems, Inc., Isanti, MN) on each hen. Additionally, hens were translocated from four other locations in Utah. Number of hens and methods for translocations can be found in Baxter et al. (2013b). We located radio-‐marked hens from the ground at nest sites using radio-‐telemetry. Following identification of nest sites, we monitored each hen until eggs hatched or the nest was depredated. After hatch, we estimated clutch size using eggshell fragments in the nest. We then located and flushed the hen ~2 times per week, observing the number of chicks each time.
As part of our statistical analysis, we compiled data for successful nest hatches from 1998-‐2012, excluding 2002 in which no nest successfully hatched. We entered data into a 49-‐day encounter history compatible with program MARK. We chose covariates (unique factors) available over the 14-‐year period that we hypothesized might affect chick survival. These covariates included year effects, temperature, precipitation, marked hen age, clutch size, hatch date, and source (translocated or resident).
We recorded 135 nests that successfully hatched over the 14-‐year period. Although our results are only preliminary, we found that year effects had the greatest influence on chick survival of any of our covariates. Overall survival of our top model was about 25%. This is comparable with Baxter et al. (2013a), as well as other Greater Sage-‐Grouse studies (Burkepile et al. 2002, Aldridge 2005, Gregg et al. 2007), although lower than Dahlgren et al. (2010).
We found Lukacs’ method to be accurate in estimating Greater Sage-‐Grouse chick survival. Moving forward, this research project funded by the ORCA grant will be a chapter in my M.S. thesis at BYU. Although I don’t officially begin graduate school until Fall 2013, this research has allowed me to get a jump start on my prospectus before entering school. The experience of writing a grant proposal, obtaining the grant, performing the research, and then reporting the results has been invaluable to me as I continue to gain skills necessary to thrive in the professional world. I offer my sincere thanks to Mr. Alan Harker for providing the funding for this opportunity.
Literature Cited
- Aldridge, C. L. 2005. Identifying habitats for persistence of Greater Sage-‐Grouse (Centrocercus urophasianus) in Alberta, Canada. Doctoral dissertation, University of Alberta, Edmonton, Alberta, Canada.
- Baxter, J. B., J. P. Hennefer, R. J. Baxter, R. T. Larsen, and J. T. Flinders. 2013a. Survival of Greater Sage-‐ Grouse chicks in Strawberry Valley, Utah using micro-‐transmitters: Does handling time negatively influence survival rates?. Western North American Naturalist In Press.