Fish Eggs Eaten by Birds May Survive After Being Excreted and Establish New Populations

Many lakes, ponds, and wetlands are not directly connected by waterways, yet they often contain the same or very similar fish species. This pattern has puzzled biologists for a long time: how do fish manage to cross land and colonize new water bodies? One frequently suggested explanation is that fish eggs adhere to the feet or feathers of waterbirds and are carried to other aquatic habitats. However, direct evidence supporting this idea has remained extremely limited, leaving it largely as speculation.

Most dispersal events occur over relatively short distances, but rare long-distance events can profoundly influence the geographic distribution of species. For aquatic organisms, crossing land represents a particularly formidable barrier. Therefore, any mechanism that enables them to overcome such obstacles carries significant ecological and evolutionary implications. In recent years, researchers have begun considering an alternative pathway: some organisms may survive after being eaten by animals and subsequently dispersed through their feces into new environments. This process, in which organisms are transported through the digestive tract of animals, is known as endozoochory.

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