Relationships between the thermal environment and activity of Piute groundsquirrels (Spermophilus mollis)

(1) We examined relationships between ground squirrel activity and operativ e temperature (T-e) in two habitats in southwestern Idaho, USA to determine how activity patterns are tied to environmental conditions and how habitat can mediate the thermal environment. (2) Midday environmental conditions w ere too hot throughout much of the active season for Piute ground squirrels to remain active in a grassland habitat. (3) Ground squirrels were most ac tive in grassland at a T-e of approximately 25 degrees C and showed a stron g bimodal activity pattern during the latter half of their active season (a fter 15 April). (4) Suitable aboveground microclimates existed throughout m ust of the season in sagebrush (Artemisia tridentata) habitats and ground s quirrels remained active throughout the day. (5) The availability of cooler microhabitats may make sagebrush a better habitat than grassland for Piute ground squirrels, especially during the latter portion of the active seaso n and in hotter than normal years. (C) 1999 Elsevier Science Ltd. All right s reserved.