A new study published this week in the journal of Ecology has found that juvenile tiger sharks (Galeocerdo cuvier) have an unexpected food item on the menu: songbirds. The study began in 2010 when lead researcher and fisheries researcher at Mississippi State University, Marcus Drymon, caught a juvenile tiger shark as part of an ongoing study in the Gulf of Mexico. When the shark was brought on the boat to be measured and tagged before release, it barfed up a mass of feathers, according to Drymon. When Drymon analyzed the feathers, it turned out they belonged to a brown thrasher, not seabird species known to be a part of the tiger shark’s diet (Drymon et al., 2019).
Videos of the Wild (Videographer). (2014). Tiger Shark Attacks and Eats Albatross Birds Learning to Fly [Video Clip]. Retrieved from https://www.youtube.com/
This study is the culmination of either years of research from 2010 to 2018. The team studied the stomach contents of 105 juvenile tiger sharks by inserting a tube into their stomachs and pumping out the contents before releasing them unharmed back to sea. Of the 105 individuals examined, 41 sharks had partially digested bird remains in their stomachs. Using visual and DNA analysis, the team was able to identify 11 species of North American land birds: the barn swallow, eastern kingbird, house wren, common yellowthroat, marsh wren, eastern meadowlark, swamp sparrow, brown thrasher, white-winged dove, yellow-bellied sapsucker, and the American coot (Drymon et al., 2019). Strangely enough, the team didn’t find a single seabird.
So how do songbirds that you’d find around your bird feeder at home end up in the stomachs of juvenile tiger sharks? Drymon and his team believe it has to do with the seasonal migrations of these songbirds throughout the Gulf of Mexico. Song birds make two seasonal migrations over the Gulf, one in the spring and one in the fall. The migration in the fall directly coincides with the birth of baby tiger sharks in the north central Gulf of Mexico. Of the 41 tiger sharks in this study that were found with land birds in their stomach contents, nearly half (46%) were neonates, new born baby tiger sharks (Drymon et al., 2019). At birth, neonates are only about 20% or less of their mature size and their predatory skills are very low, they have to hone those skills as they age. Likely they predations on land birds are the result of opportunistic foraging and scavenging (Drymon et al., 2019). During the trip, those songbirds that are old and sick may fall into the ocean where they are then preyed upon. Bad weather may also be a factor in knocking these land birds into the water, where they are then unable to take off again (Newton, 2007). Further research is needed to understand the importance of this foraging stragey to the neonate and juvenile tiger shark’s development. This study provides further evidence for a complex food network between our land and sea ecosystems than involve elasmobranchs in ways we are only just beginning to understand.
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Proceeds benefit shark research and conservation with a donation to Project AWARE!
Thanks so much for checking out exciting new elasmo research! Be sure to check out last week’s Featured Species, the Tasselled Wobbegong! And be sure to check back tomorrow for this week’s featured species. As always, leave me a comment with anything you’d love to know more about in the elasmo world! Also connect with me on Instagram and Facebook for even more elasmo fun!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finactics!
Featured Image Source
Jones, D. H. (Photographer) (2019). Fig 1. Acquiring stomach content from a live tiger shark (gastric lavage) [Digital Image]. Retrieved from https://doi.org/10.1002/ecy.2728
Drymon, J. M., Feldheim, K., Fournier, A. M. V., Seubert, E. A., Jefferson, A. E., Kroetz, A. M., & Powers, S. P. (2019). Tiger sharks eat songbirds: scavenging a windfall of nutrients from the sky. Ecology, e02728.
Newton, I. (2007). Weather‐related mass‐mortality events in migrants. Ibis, 149(3), 453-467.