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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Black Cockatoos; wailing spirits of the land

No, I haven't really gone all mystical since last year, but there is something truly thrilling about a flight of massive black-cockatoos rowing easily across the sky, their creaking wailing calls drifting down as they pass over. This is a uniquely Australian experience, as the five species all evolved here and are found nowhere else.

Yellow-tailed Black-Cockatoos Zanda funerea, part of a large flock flying over Lower Glenelg NP,
far western Victoria, under a leaden sky.

Overall there are 21 species of cockatoo that together comprise the family Cacatuidae. The only ones found outside of Australia are seven of the 11 species of the genus Cacatua, which live in New Guinea and nearby islands scattered as far as Sulawesi and the Philippines. Although the massive Palm Cockatoo Probosciger aterrimus is also black, it is much more closely related to the white and pink cockatoos.

Red-tailed Black-Cockatoo Calyptorhynchus banksii, Nitimiluk NP, Northern Territory.
Coming in to land, it shows the typical black-cockatoo characters of long rounded
wings and long tail, massive bill and overall dark plumage with coloured tail panels.
This one is moulting, currently regrowing the outside left tail feather.

Red-tailed Black-Cockatoo landing, Bourke, New South Wales, and giving
a slightly better view of the lovely tail panels.

Yellow-tailed Black-Cockatoo, Murramarang NP, south coast New South Wales,
cracking banksia cones to get at the nutritious seeds - an accomplishment that would be
fatal to our teeth! This shows better the huge powerful bill and also the typically
zygodactylous feet, though this is not a structure unique to the cockies.
The four toes are opposed with the outside two pointing backwards and the middle two
facing forwards. This is an excellent arrangement for both grasping food and for
clambering in trees. (This bird is a male, with dark bill and reddish eye-ring.)

We have now met the two genera, Zanda (with yellow or white highlights) and Calyptorhynchus (with red or orange panels). For most of their taxonomic history they have all been included in Calyptorhynchus, a name applied by the French zoologist Anselme Desmarest in 1826. It means 'covered bill' (ie the base of it, by feathers), and while true it is certainly not unique. In 1913 the somewhat erratic but highly productive Gregory Mathews, a wealthy Australian working from England, separated out the 'yellow and white' black-cockatoos and called them Zanda. Characteristically he didn't see a need to explain the name, and it might have been inspired by an Indigenous name (though probably not, as he also used it as a subspecies name for several unrelated birds) or he might simply have made it up - he had form. Also typically it didn't take on, until within the past decade when based on plumage characters (coloured bars and speckles on the 'red' females, but not the 'whites and yellows') and significant differences in begging calls of young birds, it was resurrected.

Red-tailed Black-Cockatoo pair roosting (and canoodling) in a tree by a waterhole near
Barcaldine, central Queensland, female on the right. (And try as I might I couldn't get
a vantage point where the sun wasn't behind them, though they were quite
unperturbed by us.)

Black-cockies are found throughout much of the continent except for the deep deserts, though Red-tails are found well inland where there is water. They alone are found scattered in separate populations in every Australian mainland state and the Northern Territory. Yellow-tails are found in a broad hinterland band from Eyre Peninsula in South Australia to Tasmania and the southern tropics in Queensland. They are the most familiar ones to most people, living in the heavily populated south-east. They're not typically suburban birds, though they're quite common in Canberra and are regular in and over the suburbs. Luckily for us they love the big bankia which overhangs our balcony and they drop by from time to time to sample the seeds ripening in the tough cones.

Female Yellow-tailed Black-Cockatoo in Silver Banksia, suburban Duffy, Canberra.
(She has a white bill and brown eye rings.)

This leaves three species with much more limited distributions; all are regarded as Threatened due to habitat loss (especially large hollow-bearing breeding eucalypts) and fragmentation.

The Glossy Black-Cockatoo Calyptorhynchus lathami is scattered across a large area of coastal south-eastern Australia, extending well inland in places. It is a casuarina specialist, living almost exclusively on the dust-like seeds that they extract from the cones, having selected a tree with a good proportion of ripe cones. It nips off a cone, holds it up (nearly always in its left foot) and rotates it, stripping off the woody layers and eating the tiny seeds. They must feed nearly all day to get enough. While doing so they can often be readily approached, giving themselves away by soft metallic grating creaks. 

 

They are listed as Vulnerable (ie to extinction) in each state and territory in which they occur, though the Kangaroo Island population in South Australia is Endangered.

Male Glossy Black-Cockatoo eating casuarina cones, Bawley Point, south coast
New South Wales. He has a dark bill and plain head.

Female Glossy Black, Nowra, further south down the coast. She has a white bill
and yellow-blotched head. Both sexes have red tail panels, which are the source of reports
of Red-tailed Black-Cockatoos in the south east. These are invariably incorrect
but are persistent.

While on the topics of myths around black-cockatoos, a favourite is that they are bringers of rain. Undoubtedly the two coincide on occasions, but they also turn up here regularly during drought and many a rainstorm is unheralded by cockies (or any other birds known as 'rain birds'). It's a curious one and its adherents cheerfully brush such objections aside. I admire their faith.

In the south-west of the continent are two species of white-tailed black-cockatoos, which apparently arose in wetter times when yellow-tails were able to cross from the east before the arid Nullarbor Plains closed the access. This has happened more than once and presumably the two white-tailed species arose from separate crossings, the second after the first had been there long enough to evolve into a separate species and unable to breed with their now distant relations. They are quite similar and the differences weren't recognised for a long time, until 1948 in fact. The key difference is in the beaks, which relate, naturally, to their diets. For a while they were known, logically to most of us, as Short-billed and Long-billed White-Cockatoos but (unfortunately for those of us who aren't keen on lumbering unsupecting animals with human names) they are now known as Baudin's Black-Cockatoo Zanda baudinii and Carnaby's Black-Cockatoo Z. latirostris. Both species are listed as Endangered

Carnaby's (Short-billed) Black-Cockatoos at Yanchep, north of Perth. Here they are in
their major habitat of banksia coastal heathland, where their short heavy bills are
employed in cracking open the cones, like the Yellow-tails from which they derived.

A female (white bill, large cheek patch), part of the same flock.

As well as the coastal heaths (kwongan) Carnaby's are found inland in Wandoo woodlands where there is an understorey of Banksias and related woody-seeded shrubs. They are named as a tribute to West Australian entomologist and jewel beetle expert Keith Carnaby, who recognised that two white cockatoos are present and published it in 1948. 

The 'other' species, Baudin's Black-Cockatoo, is taken from the species name, which in turn is for the French naval officer Nicholas Baudin who commanded the great scientific expedition to Australia from 1800 to 1803. By all accounts he was appallingly rude and unsympathetic to the needs of the scientists who were the point of the whole exercise, but I also note that he died on the way home and history tends to be written by the survivors.

Baudin's (Long-billed) Black-Cockatoos, Stirling Ranges NP. Unfortunately their bills are
largely obscured by the feathers (hence Calyptorhynchus!) but you get some idea of its
longer and more slender nature from the bird on the left. (I recall this morning as offering some
of the worst light I recall - at least to someone with my limited photographic skills!)

It's a pity I can't show you the bill in more detail, because it's very specialised. Like other black-cockies the top bill is very mobile, hinged to allow greater movement than that of most birds, to allow delicate grasping and great pressure to be applied. However it is also very long and slender to enable the extraction of seeds from the large woody fruit of Marri Corymbia (or Eucalyptus) calophylla, a common tree of the south-western forests and moister woodland.

The incredibly tough Marri fruits (here in John Forrest NP, near Perth) are up to 50mm long
and 35mm wide, and can form all year round, producing large numbers of seeds
over an extended period, including during the sometimes hungry days of winter.
This is a very valuable resource, worth the effort of extraction. The bill is strong
enough to crush the capsule, then the top mandible extracts the tiny seeds.

Faced with an apple, the cocky will similarly extract the seeds and ignore the flesh! This has led to many fatal interactions with orchardists, some under licence, others illegal.

 

As well as seeds, other black-cockies also eat fruit; Red-taileds are very fond of the fruit of White Cedar Melia azedarach. This tree is native to NSW, Queensland and the Northern Territory as well as across south-eastern Asia to China and Japan, and across the Pacific. It mostly lives on rainforest margins, but has been widely planted. The fruits, seeds and leaves are toxic to most mammals, but not birds. In Bourke, in far northern inland NSW (and doubtless other inland towns too), the Red-taileds can always be found in town when the White Cedar street trees are in fruit.

Red-tailed Black-Cockatoo dining in town on White Cedar fruits, Bourke.

It might be a surprise to know that they can be quite carnivorous too. Yellow-taileds are very assiduous in extracting large beetle and moth larvae from the interior of very hard eucalypts, doubtless to the surprise of the larvae who doubtless consider themselves safe there. The birds will clamber down the trunk of the tree, searching for the holes through which the grubs void their waste (frass, in case you were looking for a more technical term). It will then rip out a strip of timber with its formidable bill, until it is at about 45 degrees to the trunk, and use it as a perch from which to work, tearing the hardwood out until it reaches the luckless and luscious grub. 

Blackbutt Eucalyptus pilularis excavated by a Yellow-tailed Black-Cockatoo,
Ulladulla, south coast NSW.

They also spend a lot of time on much softer wattles too, an easier proposition from which to extract the meal, though the smaller the stem the smaller the reward too.

Yellow-tailed Black-Cockatoo working on an Acacia stem, Murramarang NP.
The holes by his left foot may be exploratory, or there may have been more
than one grub present.

So, the wonderful black-cockatoos, old Australians who still thrill us with their wailing presence in the skies, in the forests, and even, on a good day, in our yards.

Yellow-tailed Black-Cockatoo female (but you knew that!) just outside my study window,
snacking on banksia seeds and discarding the rest. I don't mind cleaning up after her..

After all, any black-cocky day is a good day.

(And because I don't want to leave the other cockies feeling miffed, I promise to write about them someday soon.)

NEXT POSTING THURSDAY 10 FEBRUARY

I love to receive your comments and in future will be notifying you personally by email when a new posting appears, if you'd like me to. All current subscribers have been added to this mailing list and have already been contacted.
This will mean one email every three weeks at the current rate of posting. 

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It's Not Easy Being Cool

Last time we talked about the wonderful toucans and hornbills, including the newly-recognised importance of their amazing bills in helping them keep cool. As promised, this time I'm going to talk more about some of the ways in which animals lose heat to avoid overheating, and a bit about the implications for this in a world which is getting warmer all the time. Hopefully it won't be too dry - as usual plenty of pictures of interesting animals! Firstly I must remind us that birds don't have sweat glands - not much point in them under feathers (or indeed fur) - so that's not an option for cooling off.

Before we leave last week's theme of large beaks with networks of surface blood vessels which can be opened to 'dump' surprisingly large amounts of heat quickly, or closed off to conserve heat where necessary, it's worth noting that hornbills and toucans aren't the only ones to practise this strategy. In fact the more that researchers look, the more examples they're finding of it. An unexpected one is among puffins, seabirds of the cold northern oceans. 

Tufted Puffins Fratercula cirrhata were shown to drop the temperature of their bill by
five degrees C within 30 minutes of landing from a foraging flight,
while heat loss from the back was negligible.
Photo per phys.com.

Why would they need to get rid of excess heat in such an environment? The answer seems to lie in observations of a close relation, the Thick-billed Murre Uria lomvia, of the North Pacific and Atlantic. Like puffins they have relatively short stubby wings for diving and chasing after food underwater, so they are not terribly efficient in the air and they must work very hard to fly. In fact the increase in their energy expenditure during flying compared to resting is the highest ever measured in a vertebrate. That, with their efficient insulation, leaves them vulnerable to over-heating, hence the use of the bill to remedy that danger. 

Last time I reported on a South African study which showed that ground hornbills lose a significant amount of heat from the bare skin on the face and neck as well as the bill. It follows that other birds with extensive bare skin on the face, especially in the tropics, are probably doing the same thing.

Blue-and-Yellow Macaw Ara ararauna, Pantanal, south-western Brazil, at nest hollow.
The large white face is bare of feathers except for the artfully arranged lines of black feathers.

It doesn't mean however that these birds are controlling the heat exchange, as the toucans and puffins are. Simply having such expanses of non-insulated skin will allow cooling to take place through blood vessels near the surface. Work on Ospreys showed that heat was lost through the long legs and claws much more than through the beak, but this wasn't managed either.

 

Birds will tuck their beak or a foot under the feathers to stop them from losing heat, but will also do so in hot weather to prevent them taking up any more heat from the air. 

 

Emus and Ostriches do regulate their heat loss, through beaks and bare or lightly feathered necks and legs plus feet and toes. This study, using infrared thermography ('heat pictures'), was done back in 1994, which surprises me.     

Emus near Esperance, Western Australia. The expanses of bare skin on
neck, legs and feet all act as controlled temperature regulators.

 

Somali Ostrich, Shaba Reserve, northern Kenya.
The same comments apply to it as to the Emu, though its barer
neck is presumably a better heat disperser. Both live in hot
arid situations (though Emus also live, or lived, in milder moister regions).

That study also looked at a Southern Wattled Cassowary, a rainforest bird, and concluded that they behaved similarly, but that the legs were less important. (The overall sample size was very small, two ostriches, two emus and the cassowary, all in Brookfield Zoo in Illinois.)  However, they reported that the casque - the big impressive spongy helmet - performed the function instead. Hitherto many suggestions had been made for its purpose (from crashing through dense vegetation to display) none of which were very convincing. Much more recently a 2019 study of 20 captive cassowaries at temperatures from 5 to 36 degrees across eastern Australia confirmed the earlier findings. The bill tip, legs and especially the casque were important in temperature control. At high temperatures they increased the blood flow to the casque, so allowing heat to escape, and when it was cold (they live in mountain rainforests as well as down near the sea) they closed it down. When it was particularly hot they would dip their head in water to increase the heat dump.

Southern Cassowary Casuarius casuarius, in rainforest, Atherton Tableland, north Queensland.

And it seems that many other birds are shedding heat through bills, skin, legs and feet, as this infrared image of an Australian King Parrot Alisterus scapularis shows. Even smaller bills are of value here.

The hottest parts (ie shedding the most heat) show as yellow - the bill,
skin round the eyes and feet. Photo per The Conversation.

The bigger you are, the smaller your surface area is relative to your mass. This is fine if you're in a cool climate, because it means you don't lose heat as easily as a smaller animal. However if it's hot you might be in trouble trying to lose enough heat to stay safe. Accordingly, an elephant's ears represent the biggest 'thermal window' of any animal (along with the bill of the largest toucans).

African Bush Elephant, Queen Elizabeth NP, Uganda.
These magnificent ears are thin and full of fine blood vessels. Even when they are
still they dump heat readily but, if that's not enough, flapping them makes them
even more efficient. (They're pretty good at hearing too!)

Near the other end of the mammal scale the bare tail of many rodents does the job too.

Fawn-footed Melomys Melomys cervinipes, Kingfisher Park, north Queensland.
(No I know you can't see much of the tail - sorry, but you know what it looks like.)

Which brings us to some behavioural tricks for getting rid of some heat (though to at least some extent most of the structures we've looked at need to be operated too).

After my last post I had an interesting but ultimately fruitless discussion with a friend about the behaviour of sea lions and fur seals in the generally cold seas of southern Australia waving their flippers and tails in the air while lolling about in the water. I couldn't see the point in such conditions, although I found it asserted widely on line that it was indeed to cool down, albeit with no evidence that I could find. If anything the reverse seemed more plausible, that it was a strategy to warm up (as long as the air is warmer than the flipper). However the discussion above about puffins suggested something else to me. The 'seals' (no real seals in Australian waters, but that's what we call them for lazy convenience) have superb insulation in the form of a thick layer of blubber and perhaps are in danger of overheating after a busy session chasing fish. Just a thought and if you have another one (or even some actual information!) I'd be very glad to hear from you.

Australian Fur Seal Arctocephalus pusillus, Narooma, south coast NSW in typical loafing pose.

And New Zealand Fur Seals A. forsteri, relaxing and waving en masse at Goolwa, near the
mouth of the Murray River in South Australia.

Many birds in warmer climes have featherless sections of skin along the underwings, so they can lose heat by exposing blood vessels just under the surface by extending their wings.

Cocoi Heron Ardea cocoi, Pantanal, south-west Brazil, exposing bare underwing
patches to lose heat from the blood vessels near the surface.
This big heron is found throughout all of South America except for the Andes.

However this Cocoi is doing something else - its beak is open and it is panting, breathing in and out while fluttering its throat to lose heat by evaporation. This is widespread behaviour among birds in hot situations.  Here are some more examples of panting, though passerines (such as the swallows and bee-eater below) for some reason never learnt the throat-fluttering trick.

Ethiopian Swallows Hirundo aethiopica (above) and
White-throated Bee-eater Merops albicollis (below), Waza, north Cameroon.
Their wings are partly open too to increase air flow over skin.
The temperature was well over 40 degrees, and we felt like panting too!

This lovely bee-eater nests up here near the Sahara (see the long tail streamers which proclaim
its breeding status) and spends winter in the rainforests of west and central Africa.

Wood Storks Mycteria americana, Pantanal.

Galápagos Cormorants Nannopterum harrisi, Isla Fernandina.
This flightless bird is the world's largest cormorant; it nests in the full sun on lava rocks.

Female Australian Darter Anhinga novaehollandiae, Winton, central Queensland.

But what are implications of a relentlessly warming world for all this? Some at least are certainly not good for birds in arid lands in particular. You can only dump heat from a bill (or other exposed body part) if the air temperature is lower than your own temperature. As air temperatures rise that window of opportunity gets smaller, but worse, once they rise above body temperature the once-beneficial bill suddenly becomes a dangerous heat absorber. On the other hand panting is still a viable option - but as droughts become more frequent and more intense a panting desert bird is put under ever-increasing stress from water loss. If you're interested my book Birds in Their Habitats; travels with a naturalist, has more on this (and many other things of course!) - I've just noticed that it's on sale too!

 

Those problems aside for now, we might expect that appendages such as birds' bills and mammalian ears would have increased in size over the last century or so. Can we test that though? Of course we can - in museums around the world are vast treasure troves of specimens waiting to be measured and to contribute to knowledge. An Australian study published in 2015 found that the bills of three common Australian parrots, and a rarer cockatoo, have increased in surface area by up to 10% since 1871.

     

Red-rumped Parrots Psephotus haematonotus....

...Mulga Parrots Psephotellus varius...

...Gang-gang Cockatoos  Callocephalon fimbriatum...

... and Crimson Rosellas Platycercus elegans all have significantly larger bills
than their recent ancestors did.

But there's yet another aspect which I've touched on too. We noted that the elephants need extra big ears to keep cool, as their large bodies have a smaller surface area than smaller bodies. The corollary of course is that smaller bodies have a relatively greater surface area, so can shed heat more readily. Bergmann's Rule accordingly predicts that individuals of a species living in warmer climates will be smaller than members of the same species in cooler places.  But what happens when a place warms over time, as of course is happening all over the world? We might predict that at least some of the animals living there might be smaller than their ancestors - and a team led by Dr Janet Gardner of the Australian National University showed just that. They measured 517 museum skins of eight Australian insect-eating birds, collected over 130 years from 1869 to 2001. Six of the species showed a decrease in size since 1950, four of them being statistically significant. 

 

White-browed Scrubwrens Sericornis frontalis...

...White-browed Babblers Pomatostomus superciliosus...

... Jacky Winters Microeca fascinans...

... and Hooded Robins Melanodryas cucullata living at the latitude of Canberra are
now the size that their relatives at the latitude of Brisbane (nearly 1000km to the north)
were before 1950, just 70 years ago.

We've covered a lot of ground, and if you're still with me - thank you! I think the topic of how animals manage their temperature (especially when it's hot) is an interesting one in itself, but the question of  the impact of a warming world on that is an even bigger and more significant one. We've learned a lot about that in recent years, and I don't for a moment imagine we're close to understanding it all.

Next time, something a bit more scenic perhaps? I'll put my mind to it.

NEXT POSTING THURSDAY 28 October
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