What functions do penguin stomach stones serve? Sex differences and seasonal changes in captive Humboldt Penguin Spheniscus humboldti

Abstract

Penguins are considered to ingest stones and retain them in the stomach to aid in buoyancy control and digestion, or they may be accidentally ingested while feeding. In this study, we recorded the behavior of several captive Humboldt Penguin Spheniscus humboldti swallowing and regurgitating stones, and examined this behavior in relation to the timing of egg-laying. We found that only females swallowed stones, and they only did so during the egg-laying period. Furthermore, the behavior was concentrated mostly during the period of eggshell formation. These observations suggest that female penguins in captivity may swallow stones intentionally to replenish the calcium they need for eggshell formation.