Book excerpt: "We conducted an aerial survey for Dall's sheep (Ovis dalli dalli) in the Liard and Nahanni Ranges of the Mackenzie Mountains on 15 August 2018 to document sheep distribution and the lamb crop. We attempted to survey the same area with the same flight lines as the previous survey in August 2011. Unfortunately, low cloud and fog prevented us from duplicating the effort in 2011; only 50% of the Liard and 40% of the Nahanni was surveyed. Sheep were classified from the air into four sex/age classes: lambs, yearlings, ewes, and rams. We used digital photographs to verify sex/age classifications of large groups. We used a handheld global positioning system to track the survey flight path and record the locations of all wildlife seen. We classified 88 Dall's sheep in 20 groups on the Liard Range and 15 Dall's sheep in four groups on the Nahanni Range. The estimated 47.3 lambs/100 ewes (pooled across ranges) were similar to that reported for 2003 and 2011 surveys. Other wildlife observed during the survey included seven moose (Alces americanus), 18 bison (Bison bison athabascae), one wolf (Canis lupus) and three pairs of trumpeter swans with goslings (Cygnus buccinator)"--Page iii.