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Ongoing telemetry studies across the GYA are being used to understand population vital rates and dynamics, spatial ecology, and competition.
What are the tractories of bighorn sheep and mountain goat populations in the GYA? We dive in to the data to find out.
Age Ratio Dynamics
Climatic Variation and Sympatry as Correlates of Age Ratios in Bighorn Sheep and Mountain Goats in the Greater Yellowstone Area
Using management data regularly collected by state and federal agencies, we indexed recruitment rates of bighorn sheep and mountain goats in the Greater Yellowstone Area (GYA) by calculating young:adult ratios. Annual and long term regional climatic conditions were indexed using data from Natural Resource Conservation Service Snotel sensors across the GYA. Linear regression models were used to assess hypotheses that recruitment rates in bighorn sheep and mountain goats in the GYA were associated with annual and regional variation in climatic conditions. The initial dataset consisted of 685 bighorn sheep lamb:ewe ratios from 21 herds since 1960 and 184 mountain goat kid:adult ratios from 18 herds since 1966. After censoring data, 369 bighorn sheep records remained, which were split into three seasonal subsets, and 123 mountain goat records remained in a single dataset. Findings suggest that recruitment rates in bighorn sheep and mountain goats were associated with annual variation in both pre-birth and post-birth climatic conditions, interacting with long term regional climate conditions. Additionally, strong interactions were found between precipitation during the birthing season and winter severity. Collectively, these findings suggest that recruitment in bighorn sheep and mountain goat populations in the GYA may be sensitive to changes in future climate conditions and that the response may vary regionally across the GYA.
written by Carson Butler
Using new and rigorous methods to understand habitat selection and expansion of the non-native, invading mountain goat.
Annual and regional climate factors may impact recruitment of bighorn sheep across the GYA.
Combining historic observations of mountain goats and bighorn sheep obtained from regional biologists to see what we can learn from data we already have.