Yellowstone Wolf Project: Annual Report 2007

Smith, Douglas; Stahler, Daniel; Guernsey, Debra; Metz, Matthew; Albers, Erin; Williamson, Libby; Legere, Nicole; Almberg, Emily; McIntyre, Richard

At the end of 2007, at least 171 wolves in 11 packs and various groups occupied Yellowstone National Park (YNP). There were fewer packs than in 2006, but the remaining packs were larger and there were more non-pack wolves (e.g., loners, temporary pairs, etc.). This represents a 26% increase from 2006 and closely matches the population peak of 174 in 2003. Ten packs counted toward the breeding pair objective for the Yellowstone Recovery Area; the Hayden Valley pack lost both breeders late in the year and did not count. One new pack, the Gardner’s Hole pack, formed but did not survive until the end of 2007 (despite producing pups). This was the first year since reintroduction that no new packs formed. One radio collared wolf from Idaho dispersed into the park in late 2007. Pack size ranged from 4 to 22 wolves and averaged 14.2, a higher average than in previous years. Average number of pups per pack in early winter was 5.8. Reproduction and pup survival (83%) was good in 2007. Each of the 12 packs present in summer had pups. The only pup produced by the Gardner’s Hole pack was on its own at the end of the year and unlikely to survive. Three packs had more than one litter: the Slough Creek and Oxbow Creek packs from the northern range, and the Hayden Valley pack (the first recorded case of an interior pack having more than one litter). Not counting over-summer pup mortality, six collared wolves died in 2007. These included two old adults (>5 years) and four adults (2–5 years). Four were males and two were females. As in past years, the leading cause of mortality was intraspecific strife (67%). Twenty-two wolves were captured and collared in eight packs. Of these, 11 were adults, 11 were pups, and 15 were female, 7 were male. At year’s end, 57 of 171 (33%) wolves were collared. Three types of radio collars were deployed: 1) VHF, 2) downloadable Global Positioning System (GPS), and 3) ARGOS. Placement of collars was dependent on monitoring objectives, and VHF radio collars were still the most commonly used collar. Wolf Project staff documented 323 kills (definite, probable, and possible combined) made by wolves in 2007, including 272 elk (84%), 11 bison (3.4%), 7 wolves (2%), 4 deer (1%), 4 coyotes (1%), 3 moose (<1%), 2 black bears (<1%), 1 pronghorn (<1%), 1 golden eagle (<1%), 1 red fox (<1%), 1 otter (<1%), and 16 unknown prey (5%). The composition of elk kills was 41% bulls, 21% calves (0–12 months), 16% cows (1–9 years old), 12% old cows (≥10 years old), and 10% elk of unknown sex and/or age. Bison kills included 6 calves (unknown sex), 3 bulls, and 2 adults of unknown sex. Preliminary examination of winter predation rates in 2007 shows a decrease in kill rate compared to previous years. Winter predation rates for the period of 1995–2000 showed wolves residing on the northern range killed an average of 1.8 elk/wolf/30-day study period. Changes in prey selection (a shift from elk calves to bull elk) and an increase in scavenging on winter-killed ungulates by wolf packs factor in to this decrease.

Yellowstone Wolf Project: Annual Report 2007

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