Impacts of Upper Respiratory Tract Disease on Olfactory Behavior of the Mojave Desert Tortoise

Upper respiratory tract disease (URTD) caused by Mycoplasma agassizii is considered a threat to desert tortoise popula- tions that should be addressed as part of the recovery of the species. Clinical signs can be intermittent and include serous or mucoid nasal discharge and respiratory difficulty when nares are occluded. This nasal congestion may result in a loss of the olfactory sense. Turtles are known to use olfaction to identify food items, predators, and conspecifics; therefore, it is likely that URTD affects not only their physical well-being but also their behavior and ability to perform necessary functions in the wild. To determine more specifically the impact nasal discharge might have on free-ranging tortoises (Gopherus agassizii), we compared the re- sponses of tortoises with and without nasal discharge and both positive and negative for M. agassizii antibodies to a visually hidden olfac- tory food stimulus and an empty control. We found that nasal discharge did reduce sense of smell and hence the ability to locate food. Our study also showed that moderate chronic nasal discharge in the absence of other clinical signs did not affect appetite in desert tortoises.