Pronghorn Antelope Upper Snake River Plain Migration Maps and Statistics

This analysis uses location data collected on pronghorn antelope that were fitted with GPS collars in Idaho for 2003 – 2020. Individuals using a winter range (as defined as a winter herd), were used for the analysis if their location data was available at the time of the analysis. Each individual’s location dataset is used to estimate winter and summer ranges, and seasonal spring and fall migration using net-squared displacement techniques (Bunnefeld et al. 2011). For pronghorn antelope, the anchor point used to measure distances from occurred near June1 since pronghorn antelope have a higher spatial fidelity to this time of year relative to more transient winter range locations. Fall and spring migration locations are used for the migration route analysis. After individual pronghorn antelope’s spring and fall migration locations are determined, a Brownian Bridge Movement Model (BBMM, Horne et al. 2007) is used to estimate the individuals Utilized Distribution (UD) during the seasonal migrations. Single seasonal migrations are then rescaled to use only the upper 99 percent volume contour. In this process the 99 percent value contour is subtracted from the UD and resulting values less than 0 are rescaled to zero. When an individual had several seasonal migrations, the resulting UDs distributions are combined and averaged to create a single UD of all the seasonal migrations conducted by that individual. Individual UDs are combined for all individuals in the winter herd with available UD information. For migration routes, the following classes were delineated based on the area’s use across the winter herd, used by 1 individual, used by two individuals to 10% of the winter herd, 10 to 20% use of the winter herd, and greater than 20% use by the winter herd. The population level UDs is used to estimate seasonal migration stopover locations. From the combined winter herd UD, the top 10% of recorded values are selected to represent population level stopovers. Upper Snake River Plain Seasonal Migration Statistics Analyzed/Prepared by: Scott Bergen December 2020 Spatial Metrics Average length of Migration: 83.8 miles Maximum Migration Length: 136.1 miles Minimum Migration Length: 30.5 miles Total Migrations Analyzed: 51 Total Number of Individuals: 33 Total Number Spring Migrations: 25 Total Number Fall Migrations: 26 Of 51 individual seasonal migrations, 51 used Brownian bridge movement models. Temporal Data Extent of Study: October 5, 2004 – November 11, 2011 Spring Migration Fall Migration Start Date Average March 24 October 10 Minimum February 27 September 18 Maximum May 12 November 5 End Date Average April 25 October 31 Minimum April 2 October 8 Maximum May 29 January 15 Duration Average 31.6 days 20.4 days Minimum 3 days 3 days Maximum 64 days 97 days Migration Use Class Statistics Use Class Acres 1 individual 511,594 Low (>2 individuals) 276,390 Medium (10-20%) 114,266 High (>20%) 166,030 Stopover 104,072