A Celebration of Weird Bills

And by 'weird bills' I don't mean the sort where someone wants you to pay lots of money to renew a subscription that you never had!

A decade ago I wrote a brief irregular series of short posts on unusually adapted bird bills; those are pretty much lost in the mists of time but I've decided to resurrect the idea and build on it for today's post. A bird's bill (or beak if you'd prefer, there's no difference) is a wonderful structure, and is the sole food-gathering tool for most birds, as well as being fundamental to preening, nest-building, chick-feeding any many courtship activities. It is not too dissimilar to the jaws of other vertebrates in comprising upper and lower jawbones (mandibles) but it is covered in a thin horny or leathery keratin sheath. The top mandible is connected by three bony prongs to the forehead and sides of the skull, so unlike in a mammal's jaw the top mandible is moveable as well as the bottom one, enabling a significant gape. 

Let's start with a couple of the biggest bills, and one of my favourite birds (though that tends to depend somewhat on which bird I'm watching at the time). 

The claim to fame of the fabulous Sword-billed Hummingbird (Ensifera ensifera) is that
it has the longest bill of any bird relative to its body size. Indeed it is also claimed to
be the only bird with a bill longer than its body. Yet another claim is that it always rests
with its bill held upwards, because it's too heavy to hold horizontally, but this female
didn't seem to realise that.

I first saw the species (this photo commemorates that occasion) in Ecuador, at the delightful Yanacocha Reserve, 6,700 hectares of cloud forest on the northern slopes of Pichincha Volcano, across the ridge from Quito. Like other precious Ecuadorian cloud forest reserves, it is run by the admirable Jocotoco Foundation. While the Sword-bill feeds on a variety of tubular flowers which don't require the remarkable length of  bill, it seems to have co-evolved with passionfruit flowers, and especially the species Passiflora mixta. Both the bird and the flower live in a long strip of high elevation cloud forest (between 2500 and 3400 metres above sea level) along the Andes.

A related species of Passiflora at San Isidro Lodge in north-eastern Ecuador. The flower tube
of P. mixta is even longer than this, and probably no other bird can reach the rich nectar
supply at the base of it.

Well that's relatively the longest of any bird bill, but what about in absolute terms? That honour seems to belong right here in Australia, with a very familiar bird - the Australian Pelican Pelecanus conspicillatus. 

A male's bill can be up to 50cm long. The famous pouch, of thin stretchable skin,
is supported by a pair of surprisingly delicate long bones, but can hold up
to 13 litres of water.

The important point is that pelicans do not carry food (or water) in the bill, but eat it immediately.
As soon as a food item, nearly always a fish, is scooped up along with the surrounding water,
the pelican presses its bill back against the breast to squeeze the water out.
As can be seen here, pelicans (along with gulls and owls) can spread the bones of the bottom
mandible to increase the width of scoop. The fish is then manipulated to be swallowed head first.

As we'd expect, in most birds (though not the ones we're looking at today) the upper and lower bill mandibles are essentially the same size and shape so that they fit together snugly when closed. However if 'biting' or tearing is required, the upper mandible is often hooked to provide grip and leverage to rip and crush flesh, hard seedcases or even wood. In this case the tip of the lower mandible is often broad and square; when closed the top hook fits over it. Here are a couple of examples.

Yellow-tailed Black-cockatoo Zanda funerea breaking open Banksia marginata cones
to extract the seeds (in our backyard in suburban Canberra.) In this situation the
force is exerted by the bottom mandible against the top, which hooks into the cone.

The same cocky species has ripped deep into this very hard-wooded Blackbutt
Eucalyptus pilularis to extract moth or beetle larvae.
Near Ulladulla, south coast New South Wales.

Wedge-tailed Eagle Aquila audax with road-killed Red Kangaroo carcase, far
north-western NSW. The hooked bill will have no trouble opening the body.

However in a few specialised cases, this hooked upper mandible is greatly attenuated for extracting edible material from within a hard case with a small access. The big apple snails (Pomacea spp.) are abundant in Neotropical wetlands, but despite (or because of) being a valuable potential food source are protected by their large, smooth, hard shells with a small opening. However two species of raptors have evolved a long slender upper mandible to solve the problem; they are snail specialists.

Snail Kite Rostrhamus sociabilis, Panatanal, south-western Brazil,
at work extracting an apple snail, above and below. (The Slender-billed Kite Helicolestes hamatus
has developed a similar bill for the same purpose.)

But snails aren't the only food hiding in a hard shell; many seeds do the same. In the south-west of Western Australia the Marri tree Eucalyptus (or Corymbia) calophylla dominates large areas of dry forest; its fruit are not entirely dissimilar from an apple snail in appearance.

Marri fruit near Perth; the cases are phenomenally hard, but a couple of bird species endemic
to the area have solved the access problem in the same way the South American kites have. Both
these birds are experts at extracting the seeds without damaging the fruits.

Red-capped Parrot Purpureicephalus spurius, Albany,
a truly glorious large parrot, and the sole member of its genus.

The key feature of the Red-capped Parrot from our perspective however is the extended upper bill, fairly clear in this picture. Experienced older birds show great dexterity in nipping off the hard ripe Marri fruit, holding it in one claw, testing it and, if it is of good enough quality, rotating it while inserting the upper bill to extract the seeds. (Green fruit are simply chewed apart.) An earlier study found that 54% of Red-capped Parrots in winter had been eating Marri seed. 

Given the value of the resource offered by Marri, it is not so surprising that another bird has independently come up with a similar solution to the issue of accessing the seed. This is Baudin's Cockatoo Calyptorhynchus baudinii, named for French commander Nicolas Baudin, sponsored by Napoleon to lead of one the most impressive exporatory expeditions ever to visit Australia, in the first years of the 19th century. (I won't digress here into the vexed question of whether we should be lumping animals with people's names, but it was certainly simpler when the two white-tailed black-cockatoos were referred to unequivocally as Short-billed and Long-billed!) As you'd expect from the previous story, Baudin's is the long-billed version.

Baudin's Cockatoos, Stirling Ranges NP. The special mandible is not as clear as it is in the
Red-capped, largely because the bill is part-hidden in feathers, though the light isn't helping.
In this pair it can best be seen in the female (with pale bill) on the left.

Baudin's Cockies are even more dependent on Marri than the Red-Capped Parrot, with wood-boring grubs comprising most of the rest of the diet. Sadly they are listed as Endangered, by the IUCN and both Western Australian and Australian governments. The single population is estimated to comprise between 10,000 and 15,000 birds; the main threat formerly was habitat clearance, while now it is regarded as a mix of loss of mature Marri trees (the key food source), competition for nesting hollows with feral Honeybee colonies, and illegal shooting (primarily by orchadists).

Another Australian cockatoo has also evolved such a bill, but for an entirely different purpose. 

Meet the Long-billed Corella, Cacatua tenuirostris, here at Urana in
south-central NSW. Its long upper mandible evolved to extract tubers, of a
native daisy species, from the ground.

Murnong, or Yam Daisy, Microseris lanceolata, here in Canberra.

The daisy is not uncommon, though never abundant, but once it was almost unimaginably profuse. Accounts from the grassy plains and open woodlands of southern New South Wales and northern Victoria tell of swathes of Murnong flowers turning the plains golden to the horizon. Their small sweet tubers were harvested by Aboriginal people, eaten raw or roasted to a delicious treacly consistency. European settlers learnt the trick from them.There are stories of wagon wheels turning up thousands of Murnong tubers from the soft soil, leaving them to rot on the surface. Then the sheep came, eating the plants and learning to push into the soil to eat the tubers as well. The plough finished the job. 

 

The corellas used to come in vast flocks to feed on them, but when the Murnongs largely disappeared so did the corellas. They rebounded when they found that the grains which replaced the Murnong were also edible, but of course this was a capital offence and the numbers fell again. Today numbers seem to have again recovered within their fairly small range of south-western NSW and western Victoria, partly due I suspect to their ability to adapt to eating the tubers of exotic weeds.

But what about the lower mandible; can that be adapted to a particular food-gathering purpose? Well of course it can - nature can do anything!

The skimmers comprise three species (one each in Africa, southern Asia and the Americas) of birds in the gull family (though until recently they were given their own family). They are distinctive birds with large bills, usually seen loafing on sand bars or mud banks either in rivers or at the coast.

Black Skimmer Rynchops niger, Pantanal, south-western Brazil.
Here you can clearly see the much longer and heavier lower mandible.

African Skimmers R. flavirostris, Queen Elizabeth National Park, Uganda.
You can click on both these photos to better see what I mean.

But for what purpose? This photo, ordinary as it is, gives you the answer.

Black Skimmer 'skimming', Isla de Chiloé, southern Chile. It is flying along steadily, just above the water, with that long lower mandible cutting the surface. When it contacts a small fish or shrimp it automatically snaps shut, flipping the snack inward. Wonderful!

OK, so much for unusually long slender bills; what about bills that seem abnormally flat and wide for scooping? No problems. Here are two examples in totally unrelated water birds. The first is the Shoebill Balaeniceps rex (ie 'king whale-head!'), sometimes referred to as a stork, but actually the only member of its entire family. Its massive bill is well over 20 centimetres long - only pelicans and some large storks have longer bills.

Shoebill, Murchison Falls National Park, Uganda.
The slightly mad-looking eyes can be a bit disconcerting, but more so I suspect
if you were about to be seized by that huge bill! They mainly prey on fish, especially
lungfish, concentrating on low-oxygen water where the fish are forced to come
regularly to the surface to breathe.

From this angle the savagely hooked tip is obvious, as well as the mass of the bill.

Across the Atlantic in the mangroves and streamside forests of the Neotropics, from Mexico to northern Argentina, lives a bird with a surprisingly similar bill to the Shoebill, but though it is equally massive relative to the bird's size, the Boat-billed Heron is only a third as big as the Shoebill.

Boat-billed Heron Cochlearius cochlearius, Pantanal, Brazil.
The very big eyes tell us that it mostly nocturnal, so we can only see it
in the very late afternoon and at night. It is probably not particularly uncommon
but because it can mostly only be seen from a night-time boat ride, it seems scarce.

The strange bill led it to be regarded as 'not-a-heron' (and there are some who would reinstate the older view that it belongs to a separate family) but the general opinion is that it is an out-lying member of the heron family. It snaps up a range of prey, especially fish and invertebrates and small land mammals, often using its bill as a scoop in a way that no other heron does that I can think of. 

While typing this I've thought of another, entirely different, group of birds with similar broad scooping bills. The frogmouths comprise a family of well-camouflaged nocturnal birds from Australia-New Guinea and south-east Asia, mostly dwellers in dense forests. The best-known however is the Tawny Frogmouth Podargus strigoides, found in open forests and woodlands throughout Australia. Their short broad bills enable them to 'swoop and scoop' on prey, from large insects and spiders to frogs, lizards and even small mammals and birds. They are related to nightjars, swifts and hummingbirds!

Papuan Frogmouth Podargus papuensis, Cairns, north Queensland.

Finally a couple of bills that really don't fit any sort of pattern used by any other birds. 

 

Toucans, from the Neotropics, have famously huge colourful bills with which they toss down fruit, and extract nestlings from tree hollows. However we now know that the driving force behind the bill is its role as a heat disperser, to manage body temperatures in the tropics.

Toco Toucan , Pantanal, Brazil.
Rather than reiterate things I've written about in detail recently, see here for more on
toucans in general and here for the temperature-management story.

Flamingoes have an extraordinary feeding behaviour, which requires an extraordinary bill. In all the birds we've looked at today, the top mandible is the larger one with the flexible lower one working against it. In flamingoes the opposite is true.

American Flamingo Phoenicopterus ruber, Galápagos Islands.
Here the lower mandible is clearer larger than the top one.

What makes this seem especially peculiar is that the flamingo then turns its head upside down in the water so that the bill is almost horizontal, to feed with its bill in the conventional bird shape - larger mandible upwards! Presumably only thus can it get its bill close to and parallel to the substrate.

American Flamingo, same location, feeding in shallow water. It is separating water and
unwanted muddy particles from food items using a large, fatty, highly sensitive tongue with
numerous fleshy protuberances (lamellae), complemented by a keeled bill also fringed with
fleshy lamellae. The tongue is used as a pump which beats from five to 20 times a minute to
suck in beakfuls of muddy water and wrigglies - including algae, small fish and invertebrates -
and to expel unwanted gunk via a complex set of movements. Remarkable.

And while all these bills are, I believe, fascinating variations, I've left one of the most peculiar and  mysterious - ie whose function has only recently been properly understood - until last. There are two species of openbill stork, genus Anastomus, one in Africa and one in Asia. They, like the Snail Kite earlier, feed on the big apple snails but their approach is quite different. There has been a lot of debate as to how they use this structure to extract the snails, not least because the process is both rapid and mostly occurs under water. It is now agreed however that despite earlier beliefs they do not break the shell, or use the gap to carry snails away.

African Openbill Anastomus lamelligerus, Entebbe Botanic Gardens, Uganda.
You can see readily enough the outward curve towards the end of the lower mandible, but not
obvious from this angle is the twist to the side, so that the tips don't meet. Stalked pads at the
tip of the upper mandible hold a big Pila snail against the ground (or underwater mud) while
the lower tip stabs past the protecting operculum to cut the muscle which holds the flesh
in the shell. Even more remarkably a narcotic in its saliva trickles down the bill to assist the
process by relaxing the snail.

Well, there's probably nowhere to go after that story, at least in my opinion. I've gone on longer than I intended, but that's the (only) problem with good stories. Maybe we can even follow this thread in different directions one day. Meantime, thanks for perservering!

NEXT POSTING THURSDAY 13 OCTOBER

 

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