Feasibility and validity of the Animal Welfare Assessment Grid to monitor the welfare of zoo-housed gorillas Gorilla gorilla gorilla

Zoos need to monitor their animals in order to evaluate to what extent animal welfare policies result in adequate welfare. Since it is usually not feasible for zoos to structurally measure corticosteroid concentrations or conduct extensive behavioural observations, zoos often rely on their caretakers to assess animal welfare using surveys. The Animal Welfare Assessment Grid (AWAG) allows zoos to quantify and visualise animal welfare based on keeper ratings. This tool has previously been used to monitor the welfare of zoo-housed animals, but it has not yet been used in practice by zookeepers. Therefore, the welfare of two groups of western lowland gorillas Gorilla gorilla gorilla was monitored daily for three months by caretakers using the AWAG to assess its usability and reliability. Behavioural observations were conducted simultaneously to validate keeper ratings of animal-based welfare indicators. This study demonstrated that the AWAG can be used to get a good indication of the welfare of an individual or group and to identify potential welfare issues. Welfare appeared to be relatively stable in the long term, which indicates that it is not necessary to perform daily welfare audits. Keepers' assessments captured more subtle changes in welfare compared to assessments made retrospectively by researchers in previous studies. Inter-rater reliability was good, but caretakers' scores did not always correspond with data from behavioural observations. Extra training, regular staff meetings and longer observation times will most likely increase the degree of detail of keeper ratings.