About Me

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Canberra-based naturalist, conservationist, educator since 1980. I’m passionate about the natural world (especially the southern hemisphere), and trying to understand it and to share such understandings. To that aim I’ve written several books (most recently 'Birds in Their Habitats' and 'Australian Bird Names; origins and meanings'), run tours all over Australia, and for the last decade to South America, done a lot of ABC radio work, chaired a government environmental advisory committee and taught many adult education classes – and of course presented this blog, since 2012. I am the recipient of the Australian Natural History Medallion, the Australian Plants Award and most recently a Medal of the Order of Australia for ‘services to conservation and the environment’. I live happily in suburban Duffy with my partner Louise surrounded by a dense native garden and lots of birds.

Thursday, 7 October 2021

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.

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This will mean one email every three weeks at the current rate of posting. 
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Thursday, 23 September 2021

Big Bills - That's Cool! Toucans and Hornbills

Believe it or not, there is a point to that title! Both these families of birds have entranced me since I first encountered them on opposite sides of the world. (I began my overseas birding adventures quite late in life, so I saw my first hornbill in 2003, and my first toucan in 2008. Since then, I've just discovered, I've coincidentally seen 24 of each - not enough of course, and I wonder if there'll ever be an opportunity to see more, or even just enjoy the same ones again.)

They belong not just to different Families but to different Orders, so are entirely unrelated. Toucans share their Order with barbets and woodpeckers, hornbills with hoopoes and not much else. What they have in common is their conspicuous great bills, sometimes to the point of being outrageous (though only to our eyes of course!). Toucans are restricted to South and Central America, while hornbills are found throughout Africa and southern Asia from India to New Guinea. Let's meet an example of each to start with.

Toco Toucan Ramphastos toco, Iguazu Falls, Argentina.
This is the archetypal toucan in many people's imaginations, unfortunately parodied
as a cartoon bird in many contexts. I readily concede that it's almost too remarkable to take
seriously, but up close it's extraordinary - the Toco's beak, relative to body size, is the largest in
the entire bird world. It's also the biggest toucan, being over 60cm long and weighing nearly 700 grams.

Female Rhinoceros Hornbill Buceros rhinoceros, Kinabatangan River, Sabah,
Malaysian Borneo. What can one say? This is a truly bizarre animal at first meeting,
and huge, far larger than the biggest toucan, being up to 90cm long and weighing
nearly three kilograms. The casque on its bill is a feature of many hornbills.
Despite being massive in the largest toucans, their beak is also remarkably light. It's a fascinating structure, comprising a network of thin bony struts, containing light spongy keratin (the protein that forms hair, skin and nails).
The obvious question of course though is 'why?', with regard to these extravagant beaks. I'm going to discuss the two groups separately for simplicity, staring with toucans. These are mostly fruit-eaters, though they'll readily take small animals, especially lizards and frogs, as they encounter them. (Many lodges attract toucans with fruit tables, as you'll see in some of the following photos.) They are also notorious nest-robbers, taking both chicks and eggs from hanging nests and tree hollows. Other birds will often attack any toucan that comes near their nest. The large bill does not seem to offer any advantages in picking and swallowing fruit - in fact a toucan has to take any food item in its bill tip and toss it back whole to swallow, so the opposite would seem to be true. On the other hand a long bill gives an obvious advantage in reaching into deep nests, especially in hollows.

Many toucans (like the Toco above) have beaks that are brightly coloured or patterned, and presumably play a role in courtship, though that was surely not the original driving force - and many others have plain-coloured beaks.

Lettered Aracaris Pteroglossus inscriptus, Chapada dos Guimarães, western Brazil.
You may want to click on the photo to see the bills better.
'Aracari' is the name used for the mostly brightly coloured members of this genus; it derives, via Portuguese, from a word from the Tupi language of coastal Brazil, now sadly lost. My guess is that the word referred to a particular species, but it's only a guess.  'Toucan' itself has the same origin, from a word like tukana. (This language also brought us words like 'jacana' and 'jabiru'.)

In 2009 a team of scientists from Canada and Brazil published a paper showing that the Toco Toucan's bill has a vital role as a 'controllable vascular thermal radiator'. In plainer words, the bill has a complex network of blood vessels which can be dilated or constricted at will to promote or control heat loss through the bill. Using infra-red cameras they could see this happening, the heat being 'dumped' from its body to its bill, and thus to the atmosphere. This is a key need for birds which live in the tropics, especially large ones and, like most toucans, spend a lot of time in the exposed canopy. At  low temperatures the blood flow to the beak is closed off, and little or no heat is lost. They conclude that the Toco's bill is 'one of the largest thermal windows in the animal kingdom, rivaling elephants’ ears in its ability to radiate body heat'. So obviously the feeding and display functions are very important in shaping the toucan's bill, but this role of a 'heat dump' is also crucial. (I should say too that in the course of researching this post, I discovered that this idea had been proposed as long ago as 1985.)

Low resolution shot from a video, showing a Toco Toucan dumping heat just before
going to sleep. The yellow is the hottest part, 10 degrees C above the temperature of the
feathers. Courtesy of Wired.
In my next post I'm going to explore ways in which some other animals deal with the need to regulate body temperature, but for now let's get back to the toucans, and meet some more.

Toucans nest in hollows, but their bills aren't robust enough for serious excavation, so they generally use hollows prepared by someone else, often a woodpecker.

Plate-billed Mountain Toucan Andigena laminirostris, Bellavista Lodge north of Quito, Ecuador.
This bird wasn't keen to let me get any closer while it was on its nest hollow.
A less-noticed feature of toucans is their feet, which are zygodactyl, that is the two middle toes grip forwards and the outer two go backwards - you might want to save this for a scrabble opportunity. Or something.
Green-billed Toucan Ramphastos dicolorus, Atlantic forests near Sao Paulo, Brazil.
You can see the foot structure quite well here, I think. You can also see another
toucan characteristic, which is the bare patch of skin around the eye. This patch
sometimes matches the adjacent bill, but not here.
All toucans are forest birds, except for the Toco, which is also found in savannahs and open woodland.
Chestnut-mandibled Toucan Ramphastos ambiguus swainsonii, Milpe Reserve,
Ecuadorian Andes, north of Quito Brazil. This is sometimes recognised
as a full species, but more usually seen as a sub-species of Yellow-throated Toucan.
There are five genera of toucans, all of which I can fortunately introduce you to, meeting more of the family by way of wrapping up this part of the post.

The green toucanets, genus Aulacorhynchus, comprising 11 species of (as you'd expect) small, mostly green, toucans of the mountain forests. Unfortunately I can only offer one here, as I've found them fairly shy and in the canopy - not this one though!

Crimson-rumped Toucanet Aulacorhynchus haematopygus, Mirador Rio Blanco, north of Quito,
Ecuador. This is a little restaurant on the way to the famed birders' mecca of the Mindo
Valley, where birds come to fruit feeders on the other side of a big window.
There are 14 aracaris, genus Pteroglossus. We met the Lettered Aracaris above; here are a few more. They tend to be brightly coloured and large-billed; as you'll see they're not at all averse to visiting feeders either.
Pale-mandibled Aracari Pteroglossus erythropygius, another visitor to the Mirador Rio Blanco
feeders. The characteristic 'teeth' of a toucan bill are obvious here.
Many-banded Aracari Pteroglossus pluricinctus, Wild Sumaco Lodge, on the eastern
slopes of the Andes in northern Ecuador.
Chestnut-eared Aracari Pteroglossus castanotis, Iguaçu Falls Brazil.
(This is the Portuguese spelling of the falls, as used in Brazil. The spelling used
above in the Toco Toucan caption is Spanish, as of course used in Argentina.)
This is a widespread and familiar toucan east of the Andes.
Collared Aracari Pteroglossus torquatus, central Costa Rica. It is found in lowland
forests from southern Mexico to Ecuador.

And lastly, an 'honorary aracari', the gorgeous and unexpected Saffron Toucanet Pteroglossus bailloni. It is so distinctive that it used to be placed in its own genus, but recent DNA work has told a different tale.

Saffron Toucanet, Trilha dos Toucanos Lodge, inland from Sao Paulo, Brazil.
This is one of many species reliant on the perilously reduced Atlantic Forests
of near-coastal Brazil.
There are six of the awkwardly named 'dichromatic toucanets', in genus Selenidera. It simply means that males and females are differently coloured. Here's an example.
Golden-collared Toucanets Selenidera reinwardtii feeding on cecropia fruit,
Wild Sumaco Lodge, eastern Andes, Ecuador.
Female above, male below.
The four mountain toucans of genus Andigena live in the high misty cloud forests of the Andes. I find them especially handsome.
Grey-breasted Mountain Toucan Andigena hypoglauca, El Cajas NP, southern Ecuador.
Finally the big 'typical toucans', genus Ramphastos, a few of which we've already met.
Channel-billed Toucan Ramphastos vitellinus, Chapada dos Guimarães, western Brazil.
This one was being very coy, but I can't leave out that lovely blue face!
Yellow-throated Toucan Ramphastos ambiguus attracted by the same cecropia fruits
at Wild Sumaca as the Golden-collared Toucanets above.
You'll probably be relieved at the news that I'm not going to go into as much detail about the hornbills, but they're too interesting and impressive to ignore, and surely you'll want to hear the answer to the question 'but what about their bills? Heat radiators too?'. The answer is 'yes, but not quite so much'. This work was done more recently, in 2016, by a group of South African researchers who were inspired by the work on toucan bills to see if the same principle applied to hornbills. They studied Southern Yellow-billed Hornbills Tockus leucomelas, a fairly small hornbill of open country, including deserts, from southern Africa. These birds did dump heat from their bills, but not quite as efficiently as the toucans did, especially at lower temperatures. This may be to do with the difficulty of losing heat by panting, which involves evaporative cooling from the inside of the mouth, in humid conditions such as the toucans experience. Hence they are forced to find alternative strategies. A dryland bird (ie a 'dry air' bird) - as long as it has access to water - can easily pant to cool itself. There is also the fact that a hornbill's bill is much heavier than that of a toucan of the same size, and the more solid structure may be less efficient at managing blood vessels than the toucan's spongy one. However the real point is that a hornbill's bill is still a very useful way of dumping excess body heat.
Eastern Yellow-billed Hornbill Tockus flavirostris, Shaba Reserve, northern Kenya.
This is a desert hornbill very similar to, and closely related to, the Southern Yellow-billeds
that the study was carried out on; indeed they were until recently regarded as the same species.
(Needless to say, I don't have a photo of them!)

More recent work (published in 2020 by another South African team) on the biggest hornbill of all reinforced this finding, though in this case the large areas of bare skin on the face and throat were also significant.

The Southern Ground Hornbill Bucorvus leadbeateri, Tarangire NP, Tanzania.
This is an enormous bird, up to a metre high and weighing up to 6kg. They prowl
through the grasslands in gangs, eating any animal they encounter, including hares,
squirrels and tortoises, though most of their food is invertebrates.
The two species of ground hornbills are now put in their own family, but
they are closely related to the true hornbills.

Uniquely, as you may well be aware from various wildlife documentaries, female hornbills seal themselves into a nesting hollow with mud, leaving only a narrow opening to allow the male to feed her, and later the chicks. When the chicks get too big she breaks out, but reseals them inside for safety until it's time for them to fledge.

I mentioned the casques on some species, which apparently act as resonating chambers. These are bony structures, adding further to the weight of the bill. As a result, hornbills not only have very strong neck muscles, but the top two vertebrae are fused for added strength.

Black-and-White Casqued Hornbill Bycanistes subcylindricus,
Entebbe Botanic Gardens, Uganda, one of a genus of mostly large African forest hornbills.
This is a male - the female's casque is smaller.

Silvery-cheeked Hornbill Bycanistes brevis, Mount Kenya, this time a female.
This one is in the  same genus as the previous bird.

Male Wrinkled Hornbill Rhabdotorrhinus corrugatus, Kinabatangan River, Sabah.
One of a group of four hornbills from Malaysia, Indonesia and the Philippines.
An Endangered species which requires large areas of undisturbed lowland rainforest.

Rhinoceros Hornbill again, Sepilok, Sabah, because just one really isn't enough!
This is the State Bird of Sarawak, also in Malaysian Borneo, but also the national bird
of Malaysia itself. Compare the black-rimmed red eyes of this male with the red-rimmed
white eyes of the female near the start of the post.
Oriental Pied Hornbill Anthracoceros albirostris, a big hornbill found widely
in south and south-east Asia.
Some species have casques that are very modest, and probably do no more than provide some structural support for the bill.

Bushy-crowned Hornbills Anorrhinus galeritus, Sepilok, Sabah.

Crowned Hornbill Lophoceros alboterminatus, Arusha, Tanzania.
 One final observation on hornbills - along with ostriches they are the only birds (as far as I know) to have 'eyebrows', which are really single filament rictal feathers. Presumably they perform the same protective role that ours do, though I wonder why more birds don't have them?

Oriental Pied Horbill, Labuk Bay, Sabah, Malaysian Borneo.
Click on the photo to see the 'eyelashes' clearly.
And I think it's time to wind this post up - thank you if you've read this far! - with three last non-casqued hornbills from African woodlands, all in the same genus.
Northern Red-billed Hornbill Tockus erythrorhynchus Shaba Reserve, northern Kenya.
Tanzanian Red-billed Hornbill Tockus ruahae, Serengeti NP, Tanzania.
What was previously 'the Red-billed Hornbill' has recently been divided into four species.
Von der Dekken's Hornbill Tockus deckeni, Serengeti NP.

And that is the end of this big-billed odyssey! If you've followed this right through, I'm grateful though of course I'll never know. I hope you've found something here that is interesting, or just enjoyable. We've covered a lot birds, countries and ideas, and that's never a bad thing, perhaps especially in these unsettling times.
As mentioned I'm going to return next time to the concept of how some animals deal with the problem of over-heating; I hope you'll join me.
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. 
I promise never to use the list for any other purpose and will never share it.
Should you wish to be added to it, just send me an email at
You can ask to be removed from the list at any time,
or could simply mark an email as Spam, so you won't see future ones.
Thank you!