First Advisor

Deborah Duffield

Term of Graduation

Spring 2022

Date of Publication


Document Type


Degree Name

Doctor of Philosophy (Ph.D.) in Biology






Zoo animals -- Effect of human beings on, Zoo visitors, Zoo animals -- Behavior, Zoo animals -- Effect of stress on, Animal welfare. Oregon Zoo (Portland Or)



Physical Description

1 online resource (xix, 224 pages)


The visitor effect on zoo animals is one of the expanding research topics in zoo animal research. As visitors are a mandatory feature of zoological institutions, understanding their effects on zoo animals is imperative for maximizing zoo animal welfare. Zoo animals are subject to many anthropogenic influences: visual, olfactory, and audible, for example. This dissertation investigates several of the effects of visitor presence and its relative influence on six mammalian species: cheetahs (Acinonyx jubatus), African painted dogs (Lycaon pictus), Asian elephants (Elephas maximus indicus & Elephas maximus borneensis), giraffes (Giraffa camelopardalis reticulata & Giraffa camelopardalis tippelskirchi), ring-tailed lemurs (Lemur catta), and red-ruffed lemurs (Varecia rubra) at the Oregon Zoo.

After-hour events are a growing attraction amongst zoological institutions as new avenues of community engagement and revenue are needed. However, the effects of such after-hour events on animals have been minimally studied, so far. Therefore, one of the goals of this study was to evaluate the impact of after hour events on several species at the Oregon Zoo. Interestingly, this study found no statistically significant effects of after-hour events on either, fecal glucocorticoid metabolite (fGM) expression (adrenal activity) or behaviors based on event type for any of the species studied. No increase in potentially problematic behaviors was observed, indicating no measurable negative influence of after-hour events on these species.

The onset of the global SARS-CoV-2 (COVID-19) pandemic created a unique opportunity to observe zoo animals without the influence of visitors for a prolonged period of time. An ad hoc study was carried out on the effects of two transition periods on a subset of the study species (giraffe and cheetah): 1) The initial closure of the Oregon Zoo (March 2020), and 2) The subsequent reopening (July 2020). In this study, no significant differences in fGM concentrations were observed between the two transition times and times with visitor presence versus visitor absence, but significant differences were found in behaviors. However, these changes were minor and could more likely be attributed to social and medical changes that occurred within the same time period for both species.

Finally, the influence of various types of sounds as a potential source of enrichment was investigated for two species of lemur: ring-tailed lemur and red-ruffed lemur. Three sound types were used as possible enrichment: spoken word, generic rainforest noise, and species-specific lemur call-backs. Behavioral responses and fGM concentrations within each sound type were compared against each other and against periods of silence. There were significant differences in exhibit use based on sound type as well as some minor, yet also significant, differences in behavior responses, but no significant correlation between fGM concentration and sound type. However, variability in weather with cold and rainy days during the study time may have had a significant impact on behavior and/or exhibit use responses. A repetition of this study in warmer weather has been suggested and may provide additional detail to identify a more definitive impact of sound type.

The conclusions of this dissertation highlight the overwhelming individuality of zoo animal responses and the importance of testing any potential effects of visitor presence and effects of sound at the individual level. While these studies found no obvious negative effects on the animals at the Oregon Zoo, each individual responded slightly differently to the various stimuli related to visitor presence or the lack thereof. Other species and other individuals of the same species may respond differently to the same stimuli, and results from this dissertation should be extrapolated with caution to other institutions, events, species, and individual. As more studies like these continue to be conducted across zoological institutions, with a multitude of species, individuals, and visitor access types (e.g., concerts, dinner events, over-night camps), animal response patterns may begin to emerge that can assist in guiding future visitor access decisions in terms of intensity, frequency, and type most conducive to ensuring good welfare of both animals and visitors.


© 2022 Laurel Berylline Fink

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