Microclimate and microhabitat selection by the Alpine Rock Ptarmigan (Lagopus muta helvetica) during summer

摘要

The Alpine Rock Ptarmigan (Lagopus muta helvetica)—which is adapted to arctic and alpine environments—is suspected to be vulnerable to climate warming, but direct evidence is limited. Microclimates within a landscape may allow species to exist in regions where the general climate appears to be unsuitable for them. We therefore investigated the diversity of microclimates in alpine habitats used by the Alpine Rock Ptarmigan in summer, and we examined whether Alpine Rock Ptarmigan select places with amicroclimate that facilitates heat dissipation during summer days. The study was done in the Haute-Savoie (northern French Alps), where ptarmigan have been equipped with radio transmitters, thus allowing direct observations. We measured the three microclimate variables which determine the thermal environment of an animal: ambient temperature (ground and air temperature),which defines the temperature gradients between the animal and the environment; wind speed, which determines convection; and solar radiation, which determines radiation uptake. Additional measurements at four contrasting mic-rotopographic sites at five locations and at two random sites in July and August showed that the typical habitat of the Alpine Rock Ptarmigan offered a wide variety of microclimates over very short distances, particularly on hot summer days. Compared with control sites at 5 m and 30 m, Alpine Rock Ptarmigan selected places with a particular microtopography and microclimate: slightly cooler places in the shade thatwere protected from the wind; often small, north-facing depressions with a medium amount of rocks and diverse ground cover. The places selected by ptarmigan during hot summer days conformed well to the requirements of both heat dissipation and predatoravoidance, and also offered food.