On a March day in Seattle, USA’s Elliott Bay—part of the Salish Sea of northwestern Washington and southwestern British Columbia—a grebe bobbing nervously among a pod of Bigg’s (aka transient) killer whales met a swift end: snatched mid-float by the ocean’s indisputed apex predator. Just days later—and thousands of kilometres south—a brown pelican in Costa Rica’s Tárcoles River fared no better, ambushed as it was by a lurking American crocodile.
These dramatic moments, captured on camera, spotlight a surprising truth: Seabirds, waterfowls, and other feathered folk often find themselves on the wrong end of the aquatic food chain, contending with underwater predators that range from orcas and crocs to sharks, seals, otters, and even bony fish.
How often do birds end up on the menu of underwater predators such as orcas and crocs? Well, in a word, frequently. In freshwater realms, everything from bullfrogs and large fish such as pike and catfish (at least one species of which will actually wriggle ashore to snag pigeons) to otters (Exhibit A, Exhibit B) and, yes, crocodilians will take birds opportunistically. (Though relationships can be complicated: Wading birds often nest in alligator-patrolled swamps and marshes—losing fallen nestlings to the reptiles, sure, but also benefiting from the built-in protection they provide from nest-raiding predators such as raccoons.)
And how about those seabirds, waterfowl, and other avian clans that spend time along seacoasts and far out over the briny bluewater of the open ocean? We’ll acknowledge off the bat that penguins—the world’s sole remaining flightless seabirds—are eaten (or at least torpedoed in target practice) by an array of marine hunters, including various pinnipeds, sharks, and orcas. Here we’ll mostly focus on flying birds, which would seem generally less vulnerable to toothy underwater beasts.
Crocodilians & Seabirds
The Tárcoles River croc’s pelican lunch wasn’t really atypical. American crocodiles in Costa Rica have been observed—and caught on camera (multiple times)—feeding on brown pelicans before. An American croc on the mangrove coast of southwestern Florida was filmed making an unsuccessful strike on a pelican in 2019. (Indeed, not just in ocean surf and estuarine lagoons but also inland freshwaters, a variety of crocodilians, from Nile crocs to American alligators, will dine on pelican at any opportunity.)
And any number of other seabirds may be taken by croc species tolerant of brackish and saltwater, such as American and estuarine crocodiles. American crocs will prey on cormorants around atolls and cays in Belize, for example. And last year, in a particularly unusual sighting, an estuarine croc snatched a pomarine jaeger—a feisty seabird that summers in the Arctic and winters out at sea—on a beach on Pelican Island in the northern Great Barrier Reef of Australia.
“We believe it is the first recorded meeting between an estuarine crocodile and a pomarine jaeger,” Queensland Department of Environment, Science & Innovation Senior Ranger Lee Hess said in a news release, “and unfortunately it was a long way to fly to end up like this.”
Orca "Games"
Circling back to the grebe-gobbling orca in Seattle, this isn’t the first time, by any means, that killer whales have been recorded seizing or otherwise messing with seabirds and waterfowl. That includes in the Salish Sea, where transient orcas chase, grab, and slap not just grebes but also common murres, marbled murrelets, scoters, common loons, rhinoceros auklets, mergansers, and brant geese, to name a few avian victims. These interactions, unwelcome and frequently fatal as they are for the birds involved, often (and maybe even mostly) appear to be non-predatory or at least non-consumptive. The whales—frequently juveniles—seem to essentially be playing with the birds, though of course this play can help a young transient orca hone its hunting chops for future goes after pinnipeds and other sea-mammals.
Among numerous other corners of the world where similar apparent play has been recorded, a study written up in a 1990 Marine Ornithology paper documented orcas harassing many Cape and bank cormorants off the coast of southern Africa. The typical routine “involved a whale approaching from behind a seabird swimming on the surface, taking the bird in its mouth, diving with it, and then leaving the dead or dying bird floating on the surface,” the authors wrote, noting that “few if any” of the killed birds were actually eaten.
The study, which discussed fieldwork done in 1986, noted that across four days in April of that year a pair of orcas were estimated to have killed nearly 300 young cormorants. “In December between seven and 24 adult cormorants were taken per day,” the paper explained. “and in that month the whales preyed upon Cape fur seals in the early morning and late afternoon and ‘played’ with seabirds throughout the day.”
It should be noted that orcas have been observed actually feeding on (and not just roughhousing with) birds besides penguins, among them gannets, petrels, kittiwakes, guillemots, puffins, and eider ducks.
And it should also be noted that numerous kinds of seabird—from storm-petrels and kelp gulls to southern giant petrels and various albatrosses—will trail orcas in hopes of scavenging from their kills. Taken as a whole, the orca/seabird ledger probably shakes out in the positive for the birds, given all the fishy and blubbery scraps that killer-whale noshing produces.
Bird-Munching Mammals
What about other marine mammals? Besides hunting penguins in some areas—let us pause and acknowledge that living, breathing penguin nightmare called the leopard seal—pinnipeds can be proficient predators of seabirds. Cape fur seals, for example, may be significant mortality factors for fledgling cormorants and gannets in the waters of southern Africa. Indeed, capable of exploiting varied and novel food sources and mastering new predatory techniques, pinnipeds can rack up quite the avifaunal kill-count in local areas. One hungry walrus along Coats Island in the Canadian Arctic Archipelago, for instance, appeared to successfully hunt 67 thick-billed murres in the course of one August day in 2002 (with its preferred feeding method being snorfling out the birds’ soft tissues and leaving the inside-out skin and skeleton). And some of this bird-hunting can take place on land: A single male New Zealand sea lion was recorded killing at least 128 nesting adult royal albatrosses on sub-Antarctic Campbell Island in January 2005, with an average daily predation rate of seven birds over the course of a number of weeks.
Even sea otters, mostly known for crunching invertebrates such as sea urchins and mollusks (oh, and melting hearts via floating naps: you’re welcome), have been known to prey on seabirds here and there, including western grebes, gulls, common loons, cormorants, and surf scoters. Less surprising is the fact that North American river otters making their living in coastal marine environments can be adept predators of seabirds such as storm-petrels and gulls—even brown pelicans.
Shark Bites
Meanwhile, piscivory is one of the go-to dietary niches for birds, but what about the other way around? All sorts of sharks will snatch a floating or diving bird if they can, it probably goes without saying. Baitballs, floating carrion, and other common food sources regularly draw pelagic birds and sharks into close proximity. And young seabirds still mastering flight can be, if you will, sitting ducks for sharks. Fledgling albatrosses learning the ropes in the Northwestern Hawaiian Islands certainly face a steep learning curve on account of tiger sharks, which seasonally beeline to atoll rookeries to hunt them.
An early 19th-century scientific report about the hunting style of the common thresher shark alleged a thresher in Dublin Bay tail-whipped a wounded diver (loon) and then consumed the bird. (Although that account faced skepticism, modern research shows threshers do indeed stun fish with their resplendently long upper caudal fins, and seabirds are considered probable menu items for the species.)
Great white sharks—occasional biters, if maybe not regular eaters, of penguins off southern Africa—are, like orcas, probably mostly a boon for seabirds as a reliable source of spoils. That said, scavenging seabirds might sometimes end up inadvertently in the crosshairs of a feeding great white. Researchers observing interactions between a white shark and seabirds attending to a fur-seal carcass in the Tasman Sea noted that larger birds—albatrosses and northern giant petrels—bobbed in the vicinity and did periodic flyovers of the shark-shadowed carcass, but didn’t actively feed. Citing similar behaviour among big-bodied seabirds elsewhere, they concluded perhaps those albatrosses and giant petrels fretted about getting targeted by the great white, whereas littler seabirds at the smorgasbord, including fairy trions and white-faced storm petrels—which showed less discretion dining as they did close to the shark—may have felt less threatened.
It’s not only seabirds and waterfowl that can end up sharkbait: Migrating songbirds making open-water crossings are vulnerable if, as often happens, exhaustion, injury, bad weather, or disorientation forces them into the drink. Dead or still alive, such doomed, waterlogged migrants become easy pickings. A 2019 study showed tiger sharks in the Gulf of Mexico swallowed a variety of migrating land birds, from barn swallows to yellow-bellied sapsuckers; the research even raised the possibility that a well-documented tiger-shark nursery in the northern Gulf might be situated and timed to allow baby sharks to feast on bird fallout there during the autumn migration.
Researchers inventorying the stomachs of Mediterranean blue sharks have found such land birds as common swifts, quail, pigeons, and mockingbirds (also swallowed by a Pacific blue shark off Baja California)—presumably eaten as migration fallout—as well as various seabirds. Even typically deepwater sharks get in on the action: In the same sea, blackmouth catsharks—which rise from the depths at night to forage closer to the surface—have been found with blackbirds and warblers inside of them.
Fish Food
Various bony fish will also eat birds if given the chance: by scavenging, of course, but also sometimes via active predation—or perhaps unintentional predation, as may have been the case with the Cory’s shearwater found in the stomach of an Atlantic bluefin tuna, which conceivably might have ingested the bird accidentally when both were going after baitfish.
A stomach-content analysis of Pacific cod off Alaska’s Aleutian Islands suggest those fish consume a decent share of seabirds such as auklets and murres, though it’s not clear how much of that comes from predation vs. seafloor-scavenging.
Another surprising bird-eater is the American monkfish or goosefish: A 2013 study showed that this bottom-dwelling ambush predator, also known as the “all-mouth” for its gaping maw, will eat the little auks called dovekies over the deeps of the Northwest Atlantic. The researchers suspect this predation likely occurs opportunistically when monkfish swimming in the water column—when migrating, for example—run into diving dovekies.
Eight-Armed Bird-Eaters
Speaking of unexpected aquatic bird predators, let’s end here: While cephalopods are usually on the losing end of avian encounters—squid are, needless to say, a big-time food source for many seabirds—remember that those brainy, always-scheming octopuses sometimes unleash their tentacles upon feathered quarry.
Top header image: timnutt, Flickr
Human Impact
Animal Behaviour
Predator vs Prey
