Interrelationships between weather, parasitic insects, and barren-ground caribou (Rangifer tarandus groenlandicus) behaviour in Northwest Territories and Nunavut.

The Bathurst barren-ground caribou (Rangifer tarandus groenlandicus) herd decreased by 90% from 1986-2009. Increased intensity of insect harassment due to climatic warming is hypothesized as a factor contributing to the decline. I monitored weather, trapped insects, and recorded caribou behavior during 2007-2009. Oestrid fly (Oestridae) presence, and mosquito (Culicidae) and black fly (Simuliidae) activity/abundance were best explained by temperature, wind speed, light intensity, barometric pressure, relative humidity, vegetation, topography, and location. Time of day and growing degree days also affected mosquito and black fly levels. Conditions favouring mosquito activity declined, while those favouring black and oestrid fly activity increased since the mid 1980s. Mosquitoes had relatively little effect on caribou behavior. Insect avoidance increased when oestrids were present or black flies were active at moderate-high levels. Understanding differential effects of macroparasites on Rangifer behavior is necessary to predict herd dynamics in the context of a changing climate across northern Canada. --P.ii.