When bivalves attack (or: bivalves vs birds, the battle continues)



Regular readers will, hopefully, have shared my surprise on learning - firstly - that oystercatchers are sometimes 'captured' and killed by bivalves, and - secondly - that someone was clever enough to photograph such an occurrence and publish it (Baldwin 1946). Prior to seeing Baldwin's paper, I might well have imagined that such cases can occur occasionally, but I wasn't aware of anyone recording them.

Today I'm very pleased to report that I'm now aware of numerous additional such occurrences: I owe a huge debt of thanks to Tet Zoo regular Dartian, who went ferreting through the ornithological literature on my behalf. As you'll see, he turned up some real gems. We can now say that sea- and wading birds of many different kinds are known to have been 'captured', disabled or even killed by bivalves on occasion. These occurrences are still comparatively rare, but they're far more numerous than I would previously had thought.

Oh - because these instances have (with the exception of the case reported by Baldwin (1946)) not been photographed (to my knowledge), I've chosen to illustrate this article with my own hilarious, imaginative reconstructions. I hope you'll forgive me for this travesty.


Seeing as the previous 'bivalve kills bird' article was all about oystercatchers, we'll start by noting that Ginn (1971) mentioned two cases involving these birds (more specifically, Eurasian oystercatchers Haematopus ostralegus). In one case, the bird was dead, and had its bill tips clamped tight inside a mussel shell. In another instance - also involving a mussel - the bird seemed unable to fly due to the extra weight and apparently drowned shortly after being observed (Gin 1971). Wow - predating on mussels is dangerous! Or, it is if you're a 'slicer'-type oystercatcher: safer to make a living by growing a hammer-like bill and breaking in through the shell, methinks (polymorphism in oystercatchers was discussed in The incredible bill of the oystercatcher). Gill (1971) also mentioned a case where a Red knot Calidris canutus was observed with a mussel clamped on its bill. The bird was alive but very weak [the drawing above shows Red knot vs mussel... I tried to make the bird look in poor condition, and for reasons that I can't recall now I also drew it in winter plumage].

While on the subject of waders, perhaps the most amazing paper reporting 'bivalve vs bird' cases is that published by Nellie Tsipoura and Joanna Burger (1999). Therein, the authors report the aftermath of a 1996 storm on the Atlantic shore of New Jersey: huge numbers of (still living) Surf clams Spisula solidissima became washed up along a 6.5 km stretch of beach along Cape May County, and a flock of about 3000 Dunlin Calidris alpina took advantage (as did gulls and various other waders).


One Dunlin was observed 'carrying' a clam, but it soon became realised that the bird was unable to fly and actually had its bill caught between the clam's valves. This bird was far from unique: Tsipoura and Burger found 39 Dunlins with trapped bills. 39!! Three of them had broken or 'badly mangled' bills, and four Dunlin and one Sanderling C. alba were observed that had their feet caught within clam shells (all were able to free themselves when approached, however). One Dunlin with a trapped bill was seen to fall into the sea and drown. 29 others of the birds that had been caught by their bills were captured by Tsipoura, Burger and their assistants, the offending clams were removed, and the birds were released after being weighed and measured (Tsipoura & Burger 1999).

This fascinating report demonstrates that Dunlin and other waders are quick to take advantage of storm-wrecked bivalves, but it also indicates that the birds are - I presume - relatively unfamiliar with these prey, and that exploitation of them involves risk. 'Death by clam' may therefore be a small, albeit regular, source of mortality among these waders (Tsipoura & Burger 1999). My adjacent drawing shows a Dunlin with a Surf clam on its bill. Because the birds discussed in the study were discovered in January, I've shown it in winter plumage.


The cases mentioned so far have all involved shorebirds. But other birds sometimes get 'caught' by bivalves too. William Post (1973) mentioned three cases observed around the shores of New York. In 1954, Post flushed a Green heron Butorides virescens from a bank on Long Island. As the bird climbed into the air, he noticed that one of its legs was hanging vertically: "a medium-sized clam was attached to one of the toes, weighting the whole leg down". The bird landed a short distance away and we don't know what became of it, or of its toe. In 1967, Post reports that Frank Enders discovered a drowned Common tern Sterna hirundo, the bill-tip of which was gripped tightly by a Venus mercenaria [this scene is reconstructed at the very top of the article]. It seems that the tern had probed into the shell while swimming in shallow water, and had then gotten caught and eventually drowned. While on the subject of terns, there's also a record of an Arctic tern S. paradisea being killed by a clam: the bird (a banded individual) was discovered in June 1937 at Orleans, Massachusetts (Cooke 1938).

Post (1973) also saw an American bittern Botaurus lentiginosus with a large mussel clamped on its leg: again, it was able to fly despite this burden [drawings above show clam-caught Green heron and American bittern].


So, lots of stuff here to think about. It's still safe to say that getting 'caught' by bivalves is rare, but nevertheless it means that there's a risk involved in messing with bivalves: they can cause disability and even death in some birds. As we saw with the New Jersey Dunlin flock, inexperienced birds (whether that's species or individuals) are almost certainly in danger when exploiting novel bivalve prey, but the risk is probably worth taking given the potential nutritional reward. Finally, the fact that birds can and do get trapped or killed by bivalves opens the door for all kinds of speculations, and on that note I leave you with the adjacent inspired illustration...

Many thanks indeed to Dartian for his kind assistance with this article. If anyone finds additional cases, please do bring them to our attention.

UPDATE: Markus Bühler kindly passed along this photo, taken in Hørsholm Museum. The bird - a Black-headed gull Chroicocephalus ridibundus - appears to have been captured (and killed?) by what I think is a freshwater Swan mussel Anodonta cygnea (though I could well be wrong on the identification there). Wow!!


For previous Tet Zoo articles on weird deaths see...

And for articles on bird bills and their form and function see...

Refs - -

Baldwin, W. P. 1946. Clam catches oyster-catcher. The Auk 63, 589.

Cooke, M. T. 1938. Some interesting recoveries of banded birds. Bird-Banding 9, 184-190.

Ginn, H. 1971. What a way to go. BTO News 48, 7.

Post, W. 1973. Some encounters between birds and pelecypods. Bird-Banding 44, 65.

Tsipoura, N., & Burger, J. (1999). Shorebirds and Surf Clams: An Unusual Interaction Waterbirds: The International Journal of Waterbird Biology, 22 (1) DOI: 10.2307/1522003.

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Okay - obviously the occurrence of this phenomenon in nature and in the scientific literature is pretty cool.

But I am WAY more impressed by your stunning drawings! The green herons are awesome (and one of my favorite birds).

The last one...well that's just plain rad.

Seriously - those are great sketches. I would know :)

Darren, Spisula solidissima is the largest clam on the East Coast. The shells can be eight inches or more, point to point. Any bird trapped by one of those monsters will be done for.

Your illustrations are quite good for visualizing the scenes â not a travesty at all! I especially like the Dunlin drawing, though the Red Knot looks appropriately frustrated.

As for the last drawing: paleontologists should watch for fossil birds with large bivalves in close proximity.

I don't know if anyone has mentioned this one yet -- but another really nice case is that of an octopus catching and eating sea birds on the Brazilian Fernando de Noronha island in the Atlantic:

Sazima & de Almeida 2008 "The bird kraken: octopus preys on a sea bird at an oceanic island in the tropical West Atlantic". Marine Biodiversity Records 1 : e47.

Abstract: "The legendary kraken, a giant cephalopod that emerged from the depths to attack ships and devour
the sailors is reincarnated here in a miniature version. We describe an oceanic island-dwelling octopus (Octopus sp. nov.) preying on a sea bird, the brown noddy (Anous stolidus) in the tropical West Atlantic. While poised on a tide pool rim the bird was quickly seized by one or two of the octopusâ arms and dragged underwater, where the octopus was lying in ambush. We suggest that this prey type hunting occurs occasionally, even if rarely documented."

--and they have some cool photos in the paper, too.

...and of course, another wonderful case of invertebrate vs vertebrate is the recently-described large theraphosid spider, Mascaraneus remotus, from the tiny Serpent Island near Mauritius -- it preys mostly on the endemic night gecko (Nactus serpensinsula), which is the largest resident terrestrial vertebrate (apart from plenty seabirds nesting on the wee lump of rock).

If one discounts the seabirds which forage out to sea, the top predator of the terrestrial food web of Serpent Island is thus an invertebrate!

Once I had seen some toads (Bufo bufo) in lake near the town where I live. All toads had fingers clamped by alive tiny bivalves of genus Corbicula. Every toad had 2 or 3 shells on its fingers.

The image that immediately comes to mind is of the unwary diver captured by a Tridacna clam, illustrated vividly in older books of the dangerous seas. I've read that the giant clam actually reacts far too slowly to endanger an unsuspecting diver, but they've always given me the willies.

Many thanks indeed to Dartian for his kind assistance with this article.

Woohoo, mentioned in dispatches! Thanks for that, Darren. Glad that my interest in biological curiosa comes in handy sometimes.


I don't know if anyone has mentioned this one yet -- but another really nice case is that of an octopus catching and eating sea birds on the Brazilian Fernando de Noronha island in the Atlantic

Yes, someone has mentioned it.

I should pass this article along to the SyFy network so they can come up with a new weekly monster movie: Megabird vs. Uberclam!

By Zach Miller (not verified) on 23 Jul 2010 #permalink

Thanks for the article, so i hate to be nitpicking, but is it not a Black-headed gull Larus ridibundus instead of Chroicocephalus ridibundus?

By randomeda (not verified) on 23 Jul 2010 #permalink

Fascinating post, Darren, and your drawings are excellent!

It's not always safe for the bird to hammer through the shell of a bivalve. In a natural history book from 1901 that I picked up in a bookstore in London (William J. Long's Fowls of the Air), there's a chapter about "sheldrakes", or "shelbirds" (from the drawings, though, the bird is a Red-breasted Merganser). The author describes a thin and weakened sheldrake that his retriever caught, and the bird had pierced both shells of a scallop with its bill, and could no longer open it. The author removed the scallop, and set the bird free; this was about the only decent thing described in the book, actually. Most of it is a load of "noble savage" nonsense about Native Americans, plus a good deal of fantastical anthropomorphism about birds, and therefore I've been altering the book with my own sketches and paints. The chapter in which the author shoots a Snowy Owl is now entirely covered with acrylic paint and drawings of owls (I took exception to that one in particular).

randomeda, the gulls were recently reclassified: the large genus Larus was broken up. Ridibundus was put in the genus Chroicephalus.

The image that immediately comes to mind is of the unwary diver captured by a Tridacna clam, illustrated vividly in older books of the dangerous seas. I've read that the giant clam actually reacts far too slowly to endanger an unsuspecting diver, but they've always given me the willies.

I can't say i know anything about the speed of shutting but the real reason why giant clams pose no threat is because the mantle lips in tridacnines are fused together so the clam is unable to open more than an inch or so, just enough to expose the zooxanthellae-bearing mantle to the light.

As an Bachelor of Fine Arts, I am entitled to be fussy about art. It's called bacheling. Under careful inspection, I find your arts to be entirely adequate. And funny.

By CS Shelton (not verified) on 24 Jul 2010 #permalink

Don't abalone occasionally manage to clamp down on the fingers and hand (paw) of the occasional and/or inexperienced would-be collector? I'd been told that for safety reasons divers use small flat pry-bars specifically to avoid their becoming caught.