Animal welfare has been defined as “a state of complete health, both physical and mental, in which the animal is in harmony with its environment. Welfare assessment is an important component in the care of all zoo animals, but is even more critical for individuals who were hand-reared because their reactions to various potential environmental stressors may be different from those of animals reared by a parent. Studies have shown animals who are hand-reared – even those who have been socialized with other individuals of the same species – may have non-typical behaviors and may react differently to stressors than animals raised by a parent. As with any animal, the difficult part is determining what might cause an animal to exhibit behaviors deviating from what is considered to be the norm for their species. Are the differences in behavior simply the result of different temperaments amongst individuals and variations in the environments of different animals, or could these differences in response to stimuli be influenced by rearing?
A study by Bertocchi et al. examined some of these ongoing questions by studying 2 adult tigers sharing an exhibit enclosure at the Parco Natura Viva Zoological Park in Verona, Italy. Both tigers were born in captivity; the male tiger was parent reared and the female tiger was hand-reared by keepers. Overnight the cats were housed in separate off-exhibit spaces and during the day they shared an outdoor area featuring lush vegetation, rocks, shelters, a pond and various types of enrichment opportunities. While tigers in the wild are solitary animals it is generally found sharing enclosures with another of the species is enriching and improves life in captivity for these animals. A researcher observed the behavior of the tigers in their shared outdoor space during morning and afternoon sessions logging a total of 900 minutes per animal. Tigers are considered to be elusive animals, and even in a zoo enclosure they spent much of their time simply not visible to observers. Overall, when they were visible to the researcher, both animals exhibited many behaviors considered to be typical of their species, spending time moving about and exploring their environment, playing individually, patrolling/marking territory, grooming, eating etc. Some differences were observed between the animals. The female was generally more active in the morning than the male, and displayed more interest in zoo visitors and keepers. The male tiger remained hidden for longer periods of time and spent more time in territorial types of behaviors, which is considered typical for males of the species.
The major difference between the two tigers lay not in the typical behaviors they displayed but rather in the abnormal behaviors only really observed in the hand-reared female tiger. The female was seen to pace, a problematic behavior well documented in wild felines housed in zoos. The female also displayed substantially more self-grooming behaviors than the male – grooming is not considered an inherently abnormal behavior but the significantly higher incidence in the female may be an indication of stress. Additionally, the female tiger also frequently attempted to engage the male in the gambling play behavior most associated with cubs or juvenile animals. The male did not respond to her behavior, suggesting perhaps the hand-reared female had not developed sufficient social skills to successfully interact with an adult of her own species. It is important to note while the behaviors described are considered atypical, they were not injurious to the individual and did not appear to affect her exhibit mate. It is difficult to determine based on observation alone whether such atypical behavior is negatively impacting the welfare of the individual, or simply odd “quirks” resulting from being raised by humans rather than a parent. To assess the stress levels of the tigers, fecal samples were collected from both tigers without interaction between humans and the tigers. Fecal cortisol levels were then measured in extracted fecal samples using the Arbor Assays DetectX Cortisol EIA kit. These data showed on average higher cortisol levels for the female tiger than her male counterpart, and substantially more day to day variability in the levels measured in her feces. This evidence, taken along with the physical behavioral assessment suggests the female tiger in this pair is less well adjusted to her current environment than her male counterpart. Whether this difference is due to her rearing or general temperament cannot be conclusively determined – but hopefully this study prompted the humans responsible for her care to experiment with changes to her environment, routine and enrichment to increase her overall level of wellbeing.