Humans generally assess animal welfare in two ways: at the population level or the individual level. For example, those who look at population-level welfare may focus on what a species needs to flourish, while individual welfare considers the inner lives and needs of each individual.  Both methods have strengths and limitations, and in some cases, they may come into conflict (especially when animals are housed together in captive settings). 

In this report, a team of scholars describes how individual- and population-level welfare assessments can complement and conflict with each other in zoo and aquarium settings. Rather than arguing for choosing one over the other, they contend that professionals should use both methods wherever possible.

Until the 1960s, the authors explain that most animal husbandry practitioners assessed welfare at the population level and focused on animals’ productivity as a welfare indicator. These population-level assessments overlooked the welfare of individual animals and enabled the inhumane practices of factory farming. In the 1960s, public critiques of factory farming led practitioners to begin assessing animal welfare at the individual level using measures like an individual’s behavior.

Zoo professionals, like other animal husbandry practitioners, currently assess the welfare of the animals under their care at the individual level. However, when zoos are focused on conserving entire species, the authors believe that they must also assess animal welfare at the population level. 

The authors go on to describe how individual- and population-level assessments of captive animal welfare can complement and conflict with each other. For example, one strength of individual-level assessments is that they account for the fact that individual animals of the same species may have different welfare needs. This strength addresses a limitation of population-level assessments, which focus on a species’s typical needs (thus ignoring how individual animals of that species may differ). At the same time, the use of these species-based standards is one strength of population-level measurements, as individual-level measurements can be time- and resource-intensive. 

Another reason the two types of welfare measurements complement each other is that population-level assessments depend on scientific knowledge of a species’s welfare needs, and zoo and aquarium professionals can gain that knowledge through individual-level assessments. A third example is that individual-level assessments rely upon accurate identification of individuals, and zoo professionals can use population-level assessments when that is not possible.

However, tensions may arise when decisions that benefit the welfare of an individual harm the welfare of their population, and vice versa. In some social species, for instance, dominant individuals may injure subordinate individuals. The authors argue that intervening to protect subordinate individuals may benefit their welfare but harm the population’s welfare, while not intervening may benefit the population’s welfare but not the individuals’ welfare. Furthermore, when meeting individual welfare needs, professionals may have to sacrifice space, time, and money that could otherwise go to meeting a larger population’s needs. 

The authors believe that in cases where individual and population welfare needs conflict, professionals need to evaluate all actions and be transparent to their stakeholders about what they are doing for their animals and why. They emphasize that zoo and aquarium professionals should use individual- and population-level assessments together wherever possible. They are so closely connected that ignoring one may limit both.

This report may be useful to animal advocates in two ways. First, it provides considerable insight into how zoo and aquarium professionals assess animal welfare in theory and practice. While many animal advocates point out the ethical problems of keeping wild animals captive, it’s important to optimize the welfare of those who are currently being held in such places. Second, the paper highlights some of the challenges these professionals face as they balance their commitments to individual animals and species populations. By understanding these commitments and how they can conflict, advocates can work together with zoo and aquarium staff to ensure they are making the most ethical decisions possible.