The modern zoo’s roles command empirical enquiry to determine the effectiveness of zoos locally and globally. Ten years ago, published work identified the need for empirical research on a diverse range of species beyond charismatic zoo megafauna. We review zoo-based research published in the decade since this original recommendation. We collectively evaluate zoo-themed research papers from those working in zoos and those external to zoos but studying zoo-housed animals. By systematically searching Web of Science^©for zoo-based research and performing inductive content analysis to code year, journal, study animal’s taxonomic classification, and research aims and outputs we evaluate trends in zoo-themed research, contrasted with trends in species holding. Significantly more birds and fish are kept compared to mammals, reptiles and amphibians, but mammals are consistently the primary research focus. Whilst output generally rises, only for birds is a steady increase in publications apparent. Husbandry evaluation is a major aim/output, but papers on pure biology, cognition and health also feature. Most publications lead to “specific advancement of knowledge” including validation of methodologies. We show that: (1) trends in species holdings are unrelated to trends in publication; (2) zoo-themed research makes meaningful contributions to science; (3) zoo researchers should diversify their aim/output categories and chosen study species to close the persisting research gaps that we have identified. Finally, we discuss our findings in the context of evident species biases within research outputs across the broader fields of zoology, conservation and ecology.

A “visitor effect” on zoo-housed species has been documented since the 1970s, with research focused on mammals (specifically primates). To broaden our understanding of the “visitor effect” in a non-mammal, we conducted a case study on a pair of hornbills, recording behavior and aviary use alongside of visitor and keeper presence. Temperature and humidity were significant predictors of visitor number, and temperature was a better predictor of hornbill exhibit use than visitor presence. Behavior was significantly affected by the presence of keepers and individual variation in behavior was noted too. Visitor number mediated any interest in a keeper by birds: high visitor number decreased a bird's interest in its keeper. Whilst only a case study on a pair of birds, our research shows that any “visitor effect” is heavily influenced by other environmental variables and that different categories of human (i.e., visitor, keeper) affect how zoo animals utilize their environment.

Strategic collection planning is essential for zoos and aquariums globally. As organizations whose primary source of income may be from visitors, zoological collections may be tempted to select large, charismatic mammal species to maintain visitor interest. Zoos and aquariums aim to breed sustainable populations of species, many of which are not mammals. While zoo advertising and marketing often showcases megafauna, there is little research on the current composition of zoo collection plans or their evolution. To investigate zoo collection planning from a global perspective, we analysed the taxonomic composition of collections in theInternational Zoo Yearbook’s list of ‘Zoos and Aquariums of the World’ from 1960 until 2018. Average proportions of mammals, birds, reptiles, amphibians, fish and invertebrates were calculated for each collection per year. Analysis revealed that in terms of species prevalence, birds were best represented, making up 31·37% of the average collection. Amphibians, by contrast, made up only 2·78% of the average zoo species. Temporal analysis revealed a significant decrease in the proportion of bird species housed in collections (P < 0·001), while a significant increase was observed for fish (P = 0·001) and invertebrates (P < 0·001). Additionally, the average number of species housed in each collection has decreased by almost a third, from 329 spp in 1960 to 225 spp in 2018. This study suggests that zoos have reduced the diversity of animals that they keep, possibly in pursuit of sustainable populations of fewer species. However, zoos and aquariums should reflect on the implications of the poor representation of the amphibian taxa.

Modern zoos and aquariums have evolved greatly since the end of the Second World War, to become centres of conservation excellence and scientific institutions for the study of animal behaviour, ecology, husbandry management. Whilst the impact of zoos and aquariums to biodiversity conservation, population management and advancement of species care is well documented, their positive impacts on society (including the communities that they are located within) is less well known. The four established aims of the modern zoo—Conservation, Education, Recreation (Engagement) and Research—provide a strong foundation for wider review and critique of the societal value of zoos and aquariums. This article synthesises what such value may be, and how it could be measured, from a systematic review of the literature pertaining to each of these four established aims. It also recommends areas of future scientific inquiry to further study the wider impact of zoos on their local communities and on human populations and behaviour more generally. Including Wellbeing as a fifth aim of the modern zoo would also cement their wider societal value. Further scrutiny of the societal value of the modern zoo enhances the value of the zoo’s living collection and the green spaces that it manages to provide accessibility to biodiversity and nature-centric education essential to long-term, planetary friendly human behaviour change.

Behavioural research requires the use of sampling methods to document the occurrence of responses observed. Sampling/recording methods include ad libitum, continuous, pinpoint (instantaneous), and one-zero (interval) sampling. Researchers have questioned the utility of each sampling method under different contexts. Our study compared computerized simulations of both pinpoint and one-zero sampling to continuous recordings. Two separate computer simulations were generated, one for response frequency and one for response duration, with three different response frequencies (high, medium, or low) and response durations (short, medium, and long) in each simulation, respectively. Similarly, three different observation intervals (5, 50, and 500 s) were used to record responses as both pinpoint and one-zero sampling methods in the simulations. Under both simulations, pinpoint sampling outperformed one-zero sampling, with pinpoint sampling producing less statistical bias in error rates under all frequencies, durations, and observation intervals. As observation intervals increased, both mean error rates and variability in error rates increased for one-zero sampling, while only variability in error rate increased for pinpoint sampling. The results suggest that pinpoint sampling techniques are effective for measuring both frequency (event) and duration (state) behaviours, and that pinpoint sampling is a less statistically biased behavioural observation method than one-zero sampling.