Dietary strategy to reduce calories, increase movement and visitor engagement in managed crocodilians

Citation

Iske CJ and Krebs J. 2025. Dietary strategy to reduce calories, increase movement and visitor engagement in managed crocodilians. In Treiber K, Brooks M, D’amato-Anderson J, Nylander J, Eds. Proceedings of the Sixteenth Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Oklahoma City, OK.

Abstract

Various crocodilians, including eight adult female American Alligators (Alligator mississippiensis), in the Eugene T. Mahoney Kingdoms of the Night exhibit at Omaha’s Henry Doorly Zoo & Aquarium have struggled to lose weight over the past five years. In the summer of 2024, it was noted that behind the scenes tours had increased to as many as ten per week. These tours utilized Mazuri^® Crocodilian Diet (5MG2) to reinforce the trained recall behavior to holding locations and facilitate the guest experience. Calculating feed used and number of tours per week, it was estimated that the weekly calories for each alligator, which averages 1,100, was more than doubled through these tours. Separately, months prior, animal care staff had discovered all American alligators in this exhibit had ingested metal foreign bodies, which had been introduced to the exhibit by guests. Recognizing this as an opportunity, zoo volunteers were stationed throughout the exhibit to deter the introduction of additional foreign bodies and increase educational experience. An aim to reduce calories from behind-the-scenes experiences and to provide educational supervised feeding opportunities led to the development of a lower calorie, freeze-dried diet item. The zoo has long used an in-house recipe for reptile gel consisting of 27% ground Mazuri® Crocodilian Diet (5MG1), 5% powdered gelatin, and 68% water. For shelf stability and buoyancy, this gel was freeze-dried and evaluated as an alternative to higher calorie commercial biscuits. The freeze-dried gel was cut and dried into 2.5×2.5 cm pieces to provide a feed alternative with ten times fewer calories and remained palatable as evaluated by consumption and behavior upon offering. However, gram for gram, the freeze-dried gel only reduced cost by 32% compared to the commercial biscuits. While ten times more freeze-dried gel could be offered isocalorically, to be cost neutral, just under two times (45.5%) more freeze-dried gel can be offered. Initial behavioral observations were conducted to assess changes in movement and location of alligators in the presence and absence of volunteers stationed with the freeze-dried feed. Results indicate alligators were in non-resting quadrants of their habitat seven times more in the presence of the freeze-dried feed compared to when it was absent. Non-resting quadrants are locations of open water, where alligators could not be resting as there is no infrastructure to do so. Behaviorally they would be hunting or lying in wait for foraging opportunities. Non-resting quadrants are also those where animals are most visible to guests. Impacts on animal weight and condition are yet to be evaluated, but through concentrated efforts from nutrition, curatorial, and education staff, an 82% reduction in foreign objects recovered from the enclosure and 54% reduction in time spent removing foreign objects have resulted. Evidence of metal foreign body ingestion has not been observed since implementation.

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