Grisly Report Raises Questions About the Cruise Industry’s Impact on Migrating Birds

Lights on ships can lure birds to their deaths, but nearly a decade after a call for more research, the scale of the problem is anyone's guess.

September 28, 2003: The rain had stopped and the night was balmy, so Carol Bocetti strolled out onto the open deck of a 14-story cruise ship, about 50 miles south of Miami. Swirling in the ship’s lights were thousands of songbirds. Bocetti spent the next 45 minutes walking the decks, where she saw Louisiana Waterthrushes, American Redstarts, Tree Swallows, and other species hunkered down in partially enclosed corners of the ship, trapped by its drafts. She found four Common Yellowthroats already dead on the deck, and watched another four die of exhaustion as they fluttered around the lights, disoriented. 

Bocetti, a conservation biologist and professor at California University of Pennsylvania, was disturbed enough by what she saw that, eight years later, she published a brief paper about it in The Wilson Journal of Ornithology. In it, she estimated that the ship may have killed as many as 240 birds that night alone, though she admitted it was a rough guess. Mostly, she used the paper as a warning that cruise ships “may pose a significant, additional, anthropogenic source of mortality that warrants further investigation,” and called on scientists to study the matter. Bocetti says her teaching load and work on the recovery of the once-endangered Kirtland’s Warbler and Delmarva fox squirrel left no time to do that research herself. Her call to action has, it seems, gone unanswered.

That experience made it particularly difficult for Bocetti to watch a short video, tweeted on April 25 by a cruise news website called Crew Center, that appears to show hundreds of dead and injured birds on the decks of a cruise ship, including Black-and-white Warblers, Black-throated Blue Warblers, and Ovenbirds. “That was a disturbing video,” she says. “It bothers me so much because the whole point of that article I put out was a call to people who have the authority or can take on a research project.” 

The video was recorded by a crew member on the unidentified cruise ship who wished to remain anonymous, according to a Crew Center post. A May 5 article from the Cornell Lab of Ornithology’s BirdCast migration mapping team put out a call for anyone with details about the incident to share them, but a spokesperson for the lab tells Audubon magazine no new information has emerged. 

While the circumstances surrounding the incident remain unclear, BirdCast’s article surmised that the ship’s lights were to blame for the avian death toll, since it’s well-established that birds migrating at night are attracted to artificial light. That attraction often proves deadly when birds collide with lit-up structures or, disoriented by the glow, flap around lights, burning precious energy they need to complete their long seasonal voyage. 

Based on the migratory routes of the species found dead on its decks, the ship was likely east of Florida and north of the eastern Greater Antilles, BirdCast reported. The incident occurred both in the thick of spring migration and as numerous cruise ships sat idle due to the coronavirus, some of them brightly illuminated with messages of encouragement during the pandemic. “Given the large number of cruise ships currently idle, and usually operational, in this region, the potential for additional events of this sort may be significant,” the article said. 

How significant is anybody’s guess. Bocetti’s paper included a back-of-the-envelope estimate that cruise ships in the Caribbean might cause up to 715,000 bird deaths in a single fall migration. That sounds awfully high to BirdCast researcher and Colorado State University ornithologist Kyle Horton. A mass-mortality event like the one in the video typically requires a confluence of factors, he says: a source of light pollution, winds that favor migration, and fog or a low cloud ceiling. “It’s probably not happening night after night,” since that combination occurs only occasionally, Horton says. “But I still think it’s not just something to write off, either. Dimming the lights on the boat would probably be the obvious solution, and it seems like an easy fix.” 

Such a solution wouldn’t be unprecedented. After an Auckland, New Zealand incident in which bright lights lured around 60 seabirds to the deck of a cruise ship and several birds died, the country’s Department of Conservation began issuing recommendations to cruise ships entering ports to dim their lights.

Bocetti says she wishes she had pressed cruise operators to take similar measures after she saw those birds die years ago. “I guess in my head it was: We need more data before we go to the industry,” she says. “I felt like I would be the crazy woman making a claim without the science.” 

Nearly a decade after Bocetti's paper was published, both she and Horton say they’re unaware of any new science to support advocates who might want to urge the cruise industry to implement bird-saving practices or technologies. 

Cruise Lines International Association, the largest group representing the industry, did not respond to multiple requests for comment.