Journal
CHRONOBIOLOGY INTERNATIONAL
Volume 21, Issue 1, Pages 57-71Publisher
TAYLOR & FRANCIS INC
DOI: 10.1081/CBI-120027982
Keywords
activity cycle; circadian rhythm; civil twilight; entrainment; photoperiod; reproduction
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Daily aboveground activity of European ground squirrels (Spermophilus citellus) in their natural habitat was recorded with a visual scanning procedure during the active seasons of 1992 and 1993. Activity patterns were analyzed with respect to time of year and to the animal's reproductive state. Aboveground activity started on average 3.9 h (SD 0.6 h, n = 37 days) after civil twilight at dawn and ended on average 3.2 h (SD 0.9 h. n = 37 days) before civil twilight at dusk. Between onset and offset of activity, 54% was spent aboveground, of which 73% was spent foraging. Activity patterns were influenced by photoperiod, rainfall, and by reproductive state. During mating, reproductively active males started activity earlier than females and reproductively inactive males. For females, time spent foraging was high during lactation. The midpoint of daily activity was at 12:16h (SD 0.37h, n=37 days). Activity patterns of European ground squirrels thus appear robustly positioned in the middle of the photoperiod.
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