A new study has found that songbirds are a remarkably common part of young tiger sharks’ diets.
The study is described in the article “Tiger sharks eat songbirds: scavenging a windfall of nutrients from the sky,” which was published today in the peer-reviewed journal Ecology. Scientists investigated the stomach contents of 105 neonate (i.e. newborn) tiger sharks collected during bottom longline surveys from 2010-18. Forty-one (or 39%) of the tiger sharks contained bird remains.
“Studies show tiger sharks will consume almost anything,” Marcus Drymon, of Mississippi State University (MSU) Extension Service and Mississippi-Alabama Sea Grant and primary author of the article, said. “What’s interesting about this study is it finds that songbirds are a fairly predictable source of food, particularly for young tiger sharks. That’s not a connection you would easily make.”
The research team used a combination of visual identification and DNA barcoding to determine which bird species the sharks had eaten. Surprisingly, they had consumed 11 different species of terrestrial birds, including barn swallow, kingbird, house wren, common yellowthroat, marsh wren, eastern meadowlark, swamp sparrow, brown thrasher, white-winged dove, yellow-bellied sapsucker, and American coot.
“None of them were seagulls, pelicans, cormorants, or any kind of marine bird,” Drymon said. “They were all terrestrial birds.”
Tiger sharks consumed migratory songbirds primarily during the fall, when the songbirds begin their journey across the Gulf of Mexico to the Yucatan Peninsula. In the article, scientists hypothesize that sudden storm events caused the songbirds to fall out of the sky. Unable to resume flight, the affected songbirds became easy prey for young tiger sharks at the water’s surface.
To investigate a mechanism behind these bird/shark interactions, the research team analyzed data from eBird, the world’s largest biodiversity-related citizen science project, which allows birders to report the locations and species of the birds they encounter. For each bird identified from tiger shark stomachs, researchers looked at the Alabama and Mississippi coast eBird bird sighting data for that year.
“In every instance, the timing of the tiger shark eating the bird coincided with the peak sightings for that species of bird off our coast,” Drymon said. “While lethal for the songbirds, it appears these interactions provide an important yet unexpected prey resource for young tiger sharks as they hone their foraging abilities.”
Coauthors of the article include Kevin Feldheim of the Field Museum; Auriel Fournier of MSU and Forbes Biological Station-Bellrose Waterfowl Research Center; Emily Seubert of MSU Extension Service; Amanda Jefferson of MSU Extension Service and Mississippi-Alabama Sea Grant; Andrea Kroetz of the National Oceanic and Atmospheric Administration National Marine Fisheries Service; and Sean Powers of University of South Alabama.