Abstract

African penguins are an endangered species with less than 22,000 breeding pairs left in the wild. Initial population losses occurred in the early 1900s with harvesting of eggs and guano.¹ Despite conservation efforts, populations continue to decline rapidly as a result of environmental and anthropogenic stressors, such as disruption of nesting sites, oil spillages, and shifts in prey availability and distribution.^2,3 In vertebrates, glucocorticoids (i.e., corticosterone, cortisol) are released by the adrenal cortex as part of the stress response, which is both beneficial and necessary for survival.⁴ However, chronic release of these hormones can result in compromised immune function, cognitive skills, reproduction, and survival.⁵ Fecal glucocorticoid metabolites (FGM) are a valuable source of endocrine information and provide a noninvasive alternative to blood to monitor hormone levels in wildlife populations.⁶ Furthermore, while blood sampling reflects activity at the time of sampling, FGM reflect chronic levels, with multiple hours of hormone accumulation in each sample.⁷

In this study, a commercially available corticosterone enzyme immunoassay (EIA) was validated for measuring FGM in dried African penguin feces by passing tests for parallelism, accuracy, and inter- and intra-assay variability. Biological validation was also carried out with African penguins housed at Mystic Aquarium to show that FGM levels increase in response to an external challenge. Samples collected before and after a veterinary exam show a spike in FGM levels (89,000–250,000 pg/g) within one hour post-examination before returning to baseline levels (∼25,000 pg/g). Seasonal data from penguin samples collected over a one-year period show FGM levels fluctuate over the course of the natural lifecycle of the African penguin including both breeding and molt. During breeding, females (70,867 pg/g) exhibited significantly higher FGM levels (p=0.0208) than males (50,238 pg/g), demonstrating clear sexual differences in these hormones. During an average two-week molting period, FGM levels in both males and females (121,100 pg/g) decreased to below baseline levels (20,380 pg/g). These data agree with a previous study by Mazzaro et al., which reported a decrease in corticosterone levels in serum collected before and after molt.⁸ This study demonstrates this method is capable of measuring physiologically meaningful changes in African penguins. Furthermore, FGM analysis is a promising tool for monitoring wild African penguin colonies undergoing different pressures, thus has potential to play a key role in conservation strategies.

Acknowledgements

We thank the Mystic Aquarium Penguin team for their expertise and assistance with this project. We also thank interns Samantha Kaiser, Felicia Hartman, Sydney Valentine, Angela James, Ashley Griffith, Kelly McLoughlin, Kyle McAuliffe, and Aly Stober for their efforts in the field and in the lab. This work was funded by the Association of Zoos and Aquariums Conservation Grants Fund #CGF18-1551 (co-funded by Disney Conservation Grants Fund).

*Presenting author

Literature Cited

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