Indigenous to moist organic soils bordering on creeks, lakes and wetlands, the star-nosed mole (Condylura cristata) is one of the most distinctive mammals anywhere on Earth. Extensively distributed throughout eastern Canada and northeastern USA, star-nosed moles are reported to inhabit subarctic regions as far north as the fifty-fifth parallel (Peterson and Yates, 1980). Active year-round, C. cristata is chronically exposed to low ambient temperatures that may persist for six or more months a year over much of the species’ range. In fact, star-nosed moles have been observed actively tunnelling through snow (Tenny, 1871; Merriam, 1884a) and even swimming and diving in ice-covered streams during winter (Merriam, 1884b; Seton, 1909; Hamilton, 1931). The small body size (40–70 g), northern distribution and conspicuous semi-aquatic habits of C. cristata (Peterson and Yates, 1980) suggest that this species may be among the most thermally challenged members of the Order Insectivora. Considering the varied and potentially stressful thermal environments encountered by C. cristata in nature, surprisingly little data exist on the energetics and thermal biology of these peculiar animals, either in air or in water (Campbell et al., 1999). From this perspective, the strategies employed by star-nosed moles to limit or prevent body cooling at low temperatures are of particular interest. One potential mechanism that could augment or substitute for primary metabolic heat production at low air temperatures is the heat increment of feeding or HIF (MacArthur and Campbell, 1994; Chappell et al., 1997; Hawkins et al., 1997). The ‘apparent’ HIF, defined as the unavoidable liberation of heat that ensues from feeding, can be partitioned into two components. The first is associated with the mechanical costs of feeding (hereafter termed ‘mechanical HIF’) and includes 301 The Journal of Experimental Biology 203, 301–310 (2000) Printed in Great Britain © The Company of Biologists Limited 2000 JEB2356 The postprandial increase in metabolic rate associated with consuming, assimilating and excreting a meal is often termed the heat increment of feeding (HIF). The metabolic heat production of star-nosed moles, Condylura cristata, held at thermoneutrality was monitored for 4 h following a single 10 min session of feeding on a ration consisting of 0 g (controls), 3.5 g or 10 g of earthworms. Coefficients for metabolizable energy digestibility and digesta passage rate of earthworms fed to C. cristata were also determined. We then tested whether feeding-induced thermogenesis substitutes partially or completely for thermoregulatory heat production in these animals exposed to sub- thermoneutral air temperatures (9–24 °C). A single feeding on earthworms had both short- and long-term effects on the metabolic rate and respiratory exchange ratio of C. cristata. The observed short-term (0–65 min) rise in metabolic rate, assumed to be associated primarily with the physical costs of nutrient digestion, absorption and excretion, was similar to the calculated mean retention time (66.7±7.8 min; mean ± S.E.M., N=5) of this species. This component of the HIF represented 2.9 % of the food energy ingested by moles fed a single 3.5 g (13.21 kJ) meal of earthworms and 1.4 % of the food energy ingested by moles fed a single 7.5 g (28.09 kJ) meal of earthworms. At all test temperatures, resting metabolic rate typically remained above fasting levels for 1–4 h following ingestion of the high-protein earthworm diet. This protracted rise in metabolic rate, presumably associated with the biochemical costs of amino acid oxidation/gluconeogenesis and ureagenesis, averaged 12.8 % of the metabolizable energy and 8.7 % of the gross energy intake. Despite the potential thermoregulatory benefit, we found no evidence that biochemical HIF substitutes for facultative thermogenesis in star-nosed moles exposed to low air temperatures. Key words: heat increment of feeding, metabolism, energetics, digesta passage rate, digestibility, star-nosed mole, Condylura cristata, Insectivora, thermoregulation, earthworm. Summary Introduction POSTPRANDIAL HEAT INCREMENT DOES NOT SUBSTITUTE FOR ACTIVE THERMOGENESIS IN COLD-CHALLENGED STAR-NOSED MOLES (CONDYLURA CRISTATA) KEVIN L. CAMPBELL*, IAN W. MCINTYRE AND ROBERT A. MACARTHUR Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 *Present address: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (e-mail: campbelk@zoology.ubc.ca) Accepted 1 November; published on WWW 22 December 1999