Biodetectors

Six castrated male ferrets were acquired at 15 weeks of age from Marshall BioResources (North Rose, NY) and trained as described in a previous study (PONE-D-20-11704R1). Ferrets were pair-housed at the National Wildlife Research Center (Fort Collins, CO) in two level wire cages (MidWest, Muncie, IN) and maintained at 23°C on a 12 hour light (12 hour dark) cycle. The ramp connecting the upper and lower levels of the cage could be locked in a closed position, allowing each of the ferrets to be isolated. Environmental enrichment was provided both in the cages (blankets, hanging cubes, and hammocks) and during 60 minute free exercise periods daily on weekdays. Ferrets were given ad libitum access to tap water and Totally Ferret Complete diet (Performance Foods, Broomfield, CO) with the exception of food restriction periods during training and testing.

During food restriction periods, ferret body masses were recorded every weekday and health was assessed daily (e.g., grooming, activity, visible signs of discomfort). There was no food restriction on weekends and ferrets were assessed for health daily by Animal Care staff. Food was provided after training or testing sessions for 1 hour while the ferrets were separated on different levels of the cages. Food bowls were weighed before and after the feeding session and the difference (i.e., mass of food assumed ingested) was recorded. Food and/or water restriction has been shown to be required for reliable operant conditioning responses in rats and minimally stressful in terms of behavior, appearance and physiology [14, 15]. Ferrets have also been shown to respond to operant conditioning tasks reliably with food restriction with little or no signs of stress [13].