Captive domesticated zebra finches ( Taeniopygia guttata) have increased plasma corticosterone concentrations in the absence of bathing water

Keeping animals in captivity should always favour conditions that aim to improve their welfare with respect to species-specific requirements. For laboratory animals, the majority of welfare issues have been explored in rodents thus far, whereas the effect of housing conditions on the well-being of avian lab species has received relatively little attention. Here, we investigate the importance of access to a water bath in captivity on the welfare of a drought-adapted passerine, the zebra finch (Taeniopygia guttata). Zebra finches can survive long periods of drought in the wild, which also includes a lack of surface water for bathing, but if water is available, they regularly take the opportunity to bathe in water. Water baths represent an important comfort behaviour for zebra finches, especially because the birds do not take dust baths. Here, we wanted to examine the role of the opportunity for water baths in relation to corticosterone concentrations as an indicator of well-being in captive zebra finches. We sought to determine how important it is to provide water baths to zebra finches in captivity. Therefore, we repeatedly quantified the basal plasma stress hormone levels, i.e., corticosterone (CORT), and the body weight of individuals over a three-month period. During this time, control birds had permanent access to a water bath, while treatment birds experienced a 30-day period without the opportunity to bathe during the second month. We demonstrate that zebra finches lacking bathing opportunities show higher basal plasma CORT concentrations (GLM, p = 0.034) but do not differ in body weight in comparison to control birds (GLM, p = 0.31). Our results show that even for birds that can tolerate long periods of drought in their natural habitat, access to a water bath is essential for their well-being and their welfare, and thus, water baths should be provided under captive housing conditions. As chronically elevated stress hormone levels can have short-and long-term detrimental effects, our findings have important implications for welfare considerations in the management of one of the most used laboratory birds.