Improvement of breeding success is key to capercaillie Tetrao urogallus conservation in Scotland. However, factors affecting breeding success are not fully understood, including the cause of nest loss. We monitored 20 capercaillie nests with video or digital cameras at Abernethy Forest, Scotland to measure nest loss, determine causes of losses, and describe nest attendance by females. The mean date for the onset of incubation was 15 May and mean clutch size was 7.25 eggs. During incubation, females usually left the nest twice a day (range: 0–4), on average 28 minutes after sunrise and 2 hours 13 minutes before sunset, for a total of 53 minutes per day. There were no egg losses during egg laying, and the daily loss of clutches during incubation (26 days) was 0.0427 (95% CI = 0.0191–0.0663). However, an experiment with artificial nests suggested that predation rates were higher where video cameras were installed than at nests where they were not. After adjusting for the potential effect of deployment of the video system, the daily loss of the capercaillie nests was 0.0205 (95% CI = 0.0074–0.0554). Thus, the probability of a nest failing was 0.68 (95% CI = 0.39–0.83, unadjusted) or 0.42 (95% CI = 0.18–0.77, adjusted). This adjusted estimate at Abernethy Forest was close to the mid-range of other studies of capercaillie nest loss in Scotland and elsewhere in Europe. Eleven of the nests were depredated, nine by pine martens Martes martes and two by unknown predators. One nest was abandoned. Based upon unadjusted daily predation rates, predators destroyed 65% of nests (57% known to be by pine martens) or, after adjusting for the potential effect of the video system, 39% of nests (33% known to be by pine martens). A better understanding of factors affecting pine marten (a protected species in the UK) numbers and hunting patterns is required before a habitat management plan can be implemented to reduce pine marten predation on capercaillie nests.