Effect of insect harassment on the behaviour of the Riviere George Caribou

Recent studies on the body condition of females of the Riviere George caribou herd (RGH) in northern Quebec have shown that fat reserves declined markedly during the first month of lactation. For many populations of reindeer and caribou, it is widely accepted that insect harassment can affect food intake, energy expenditure, and consequently the accumulation of body reserves. To assess the role of biting and parasitic insects on caribou body condition, we monitored the behaviour and habitat use of RGH females from late June to early August in summers 1992 and 1993. In 1992, biting insect activity started on 27 July, while in 1993, insects were active from 14 July. Oestrids were present on the post-calving range in 1993 only. In both summers, we observed caribou harassed by flies on only four days. When insects were present, harassment reduced the time spent feeding from 53% to 30%, increased the time spent standing from 1% to 39%, and modified habitat use towards snow patches. Insect harassment had a significant impact on caribou behaviour, but its contribution to the negative energy balance during the first month of lactation seems negligible.