Timing, distances, and durations of above-ground activity were monitored du
ring three successive years in wild populations of dwarf hamsters (Phodopus
). Both P. campbelli (Djungarian hamsters) and P. sungorus (Siberian hamste
rs) were nocturnal. However, P. campbelli arose earlier (before dark or soo
n after dark versus well after dark) and remained above ground 2.5 times lo
nger than P. sungorus. Longer expeditions allowed female P. campbelli to tr
avel farther than both sexes of P. sungorus at the same speed. In contrast,
P. campbelli males were active for the same amount of time as females but
travelled almost three times faster, covering much greater distances and la
rger areas. Patterns of wheel running by females in the laboratory confirme
d the earlier onset and longer duration of activity in P. campbelli, demons
trating that differences between species in the wild were not simply respon
ses to different environmental stimuli. Activity before and after dark and
prolonged activity throughout the dark are interpreted as evidence that res
ource acquisition in the colder, drier, more seasonal habitat of P. campbel
li requires more energy and time than resource acquisition in habitat of P.
sungorus. As such, constraints on energy and time during the breeding seas
on may have been important in the evolution of biparental care in P. campbe
lli but not P. sungorus.