Reindeer summer activity pattern in relation to weather and insect harassment

Abstract

Summary 1.During the brief growing season in Arctic and high mountain ecosystems, undisturbed grazing is crucial in order to maximize growth and fattening. During summer 1997 we investigated the influence of weather and insect harassment on the behaviour and group dynamics of reindeer ( Rangifer tarandus tarandus L.). 2. Climatic data, activity of parasitic flies, and female reindeer behaviour were recorded from two wild reindeer populations in Southern Norway. Temperature and solar irradiation were good predictors of oestrid fly activity. Throughout the warm summer, reindeer were exposed to vigorous oestrid fly harassment, which caused dramatic decrease in feeding and lying, and increase in walking, running and standing. This behavioural change may compromise the physical condition of individuals entering winter. 3. Mosquitoes had little influence on reindeer activity patterns. In the absence of oestrid flies, weather parameters had no influence on reindeer activity pattern. Even during the warmest days, no signs of heat stress were recorded. Accordingly, snow patches, marshes and windy mountaintops were used primarily to avoid oestrid fly harassment. Thus, most disruptions of feeding that are often reported on warm days are responses to oestrids, not thermal stress.

In a warmer Arctic, mosquitoes avoid increased mortality from predators by growing faster

“…In 2012, when the ponds melted earlier, mosquito emergence closely coincided with caribou calving. Insect harassment drives caribou movement [13,39,40], often to insect-free areas such as snow patches and wind-exposed sites at high elevations that offer less food [13,41,42]. Reduced food intake, caused by phenological mismatch with plants or increased time spent avoiding insect harassment, can decrease calf production and increase calf mortality [27].…”

“…Average temperatures in the Arctic have increased at twice the global rate in the past 100 years [11,12] and the low biodiversity of Arctic ecosystems provided a natural but relatively simple predator -prey interaction for this study. Our focal prey population was the Arctic mosquito, Aedes nigripes Zett (Kalaallisut: ippernaq; Diptera: Culicidae), a univoltine insect that can be a significant pest to humans, caribou and other wildlife [13]. First, we integrated field observations with laboratory experiments to quantify the effects of temperature on immature mosquito development rate and the rate of mortality from predation.…”

Habitat use by semi-domesticated reindeer, estimated with pellet-group counts

“…index; f Resort = distance to tourist resort or hut; g Trail = distance to hiking trail; h Div = diversity index. Hagemoen & Reimers, 2002;Skarin et al, 2004;Syroechkovskii, 1995). The summers of 2002 and 2003 were very warm, especially in Vaisa (the mean temperature in July was 3 °C and 6 °C above normal in Vaisa 2002 and 2003 respectively).…”

“…It is known that Rangifer avoid predators (Rettie & Messier, 2000) and select forage quantity (Mårell et al, 2002) at large spatial scales, and select patches with forage of high nutritive quality at finer scales (Johnson et al, 2001;Mårell et al, 2002). Other known limiting factors for reindeer and caribou in the snow-free season are harassment from insects such as oestrid flies and mosquitoes (Downes et al, 1986;Hagemoen & Reimers, 2002;Colman et al, 2003). Thus, at the larger spatial scales there should be a selection against areas with high levels of insect harassment.…”

Predation risk and optimal foraging trade-off in the demography and spacing of the George River Herd, 1958 to 1993

“…Moreover, in the absence of oestrid flies, weather parameters had no influence on reindeer activity pattern. (Hagemoen & Reimers, 2002;Colman et al, 2003). Without mosquito har¬ assment the scattering bands left the overgrazed June/July tundra and moved toward more abun¬ dant phytomass west in the taiga.…”