Field cost of activity in the kit fox, Vulpes macrotis

Field metabolic rates and daily movement distances were measured in 26 indi vidual kit foxes (Vulpes macrotis) over a 29-mo period in the southern Moja ve Desert of California. Kit foxes traveled long distances (up to 32 km d(- 1)), with males usually traveling farther than females. Daily movement dist ances were affected by season, since males traveled the greatest distances in spring and females traveled farthest in summer. Individual foxes tracked multiple times demonstrated repeatability of daily movement distance betwe en nights, between summer and winter, and between consecutive winters. The field cost of activity per unit distance was estimated as 15.6 kJ km(-1) fr om the partial regression coefficient of a multiple linear regression model , a value not significantly different from the incremental cost of locomoti on derived from laboratory measurements. The field cost of activity was not affected by season, despite the expectation of higher costs of activity in the winter with increased thermoregulatory expenditure. The large daily mo vement distances resulted in significant activity energy expenditure (11%-3 3% of field metabolic rate), with a mean of 21% of field metabolic rate exp ended in activity during nonreproductive seasons.