Visitors are a prominent feature in the lives of zoo animals, and their presence can cause a range of impacts on zoo animals (typically classed as positive, negative or neutral impacts), commonly referred to as the ‘visitor effect’. This paper quantitatively collates the literature on the visitor effect in non-primate species, investigates the types of measures used to assess impacts of visitors on animals and considers whether impacts vary across non-primate species in zoos. In total, there were 105 papers which had investigated the impact of zoo visitors on 252 non-primate species/species groups. There has been a steady increase in visitor effect research in zoos since 2012 and this body of work incorporates species from avian (28% study species), reptilian (9%), amphibian (2%), fish (4%) and invertebrate taxa (1%). However, there is still a bias towards mammalian species (56%). The response to visitors varied across taxa. Amphibians responded negatively to visitors more frequently than would be expected by chance (p < 0.05), birds responded neutrally more frequently than would be expected by chance (p < 0.05) and fish responded neutrally and ‘unknown’ more frequently than would be expected by chance (p < 0.05). This review highlighted a number of animal-based metrics which have been used to assess the impacts of visitors on animals, with measures used varying across taxa. Moving forwards, it is recommended that moving forwards researchers incorporate a suite of measures, incorporating those which are meaningful in terms of being representative of individual animal experiences and animal welfare, collected in a manner which should capture those metrics accurately.

Marine mammals have been successfully maintained under human care; however, the media, public, and professionals within the field frequently voice welfare concerns. This study systematically surveyed peer-reviewed (PR) literature from 1948 to 2024 (n = 1308) and included an opportunistic sample of non-peer-reviewed (NPR) literature from the past 40 years (n = 756) to evaluate research efforts associated with species housed in zoos and aquariums. The current study updates and extends previous efforts to assess research categories. The findings indicate that the volume of research published mirrors the species abundance in human care. Across taxa, PR papers concentrate on science that enhances the understanding of biological functions (Acoustics, Biology, Breeding, Behaviour, Health) but is not necessarily tailored to improve management or optimal care. In contrast, a substantial portion of the NPR literature focuses on daily handling and management, highlighting Environment and Management and Enrichment-related activities. While welfare-related research has increased in both PR and NPR literature, this review underscores the need for additional welfare-related empirical studies to further enhance animal care and wellbeing. We encourage those involved in the practical care of such taxa to empirically evaluate these interventions and disseminate their findings in the PR literature.