Boise River Elk Migration Map and Statistics

This analysis uses location data collected on elk that were fitted with GPS collars in Idaho for 2007 – 2019. 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). Fall and spring migration locations are used for the migration route analysis. After individual elk 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. Depending of the frequency of the location data, either a BBMM or a Forced Motion Variance model (FMV) are used as an estimate of that season’s migration UD. If locations collected at a less than 7hr schedule, the migration used BBMM modeling techniques. If the schedule was greater than 7 hrs a FMV modeling technique was used (Fatteberge et al, in review). Further, FMV techniques that allowed for a 14 hour gap in location schedule were preferred over FMV models that used a maximum of 27 hr gap. 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 then 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 2individuals to 10% of the winter herd, 10 to 20% use of the winter herd, and greater than 20% use by the winter herd. The combined individual UDS are aggregated to estimate winter herd stopover locations. From the combined winter herd UD, the top 10% of recorded values are selected to represent population level stopovers. Boise River Elk Migration Statistics Analyzed/Prepared by: Jodi Berg and Scott Bergen Feb 2021 Spatial Metrics Average length of Migration: 26.1 miles Maximum Migration Length: 63.5 miles Minimum Migration Length: 6.4 miles Total Migrations Analyzed: 71 Total Number of Individuals: 39 Total Number Spring Migrations: 50 Total Number Fall Migrations: 21 Of 71 individual seasonal migrations, none used Brownian bridge movement models with an 8-hour time-lag, 25 used forced motion variance (1400 m) models with a 14-hour time-lag, and 46 used force motion variance (1400 m) models with a 27-hour time-lag. Temporal Data Extent of Study: March 1, 2015 – January 2, 2020 Spring Migration Fall Migration Start Date Average April 8 November 30 Minimum February 16 October 18 Maximum May 26 December 27 End Date Average April 26 December 20 Minimum March 2 November 5 Maximum July 28 January 30 Duration Average 23 18 Minimum 3 3 Maximum 73 62 Migration Use Class Statistics Use Class Acres 1 individual 692,211 Low (>2 individuals) 310,612 Medium (10-20%) 123,624 High (>20%) 25,550 Stopover 38,657