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It’s hot and sunny, so birds lie down and sunbathe


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It’s hot and sunny here in the UK right now, and elsewhere in the world too, I’m sure. In celebration of the current conditions, I figure now is a good time to recycle a Tet Zoo ver 3 article that’s already two years old: my brief review of sunbathing postures in dinosaurs. By which I mean birds. So, here it is again, with a few updates and new images. Enjoy!

To those academically interested, note that there’s a fairly extensive literature on sunbathing in birds and on the groups that practise it, on the postures they adopt, and on the function it might have (e.g., Hauser 1957, Kennedy 1969, Horsfall 1984, Simmons 1986).

Sunbathing male Elliot's pheasant at Birdworld, Alice Holt Forest, Surrey (UK). Photo by Darren Naish.

We’ll start with gallinaceous birds. The adjacent photo shows a sunbathing Elliot’s pheasant or Bar-backed pheasant Syrmaticus ellioti with one wing slightly fanned out and the tail slightly spread. I’ve seen cracids, domestic chickens and other gamebirds do the same sort of thing (below, we see a cracid stretching one of its wings out in an apparent bit of sunbathing behaviour), and this got me wondering if waterfowl (close relatives of gamebirds within the clade Galloanserae) do the same thing – I’ve never seen a sunbathing duck or swan.

Sunbathing cracid. Here's a quiz: identify the cracid! Photo by Darren Naish.

Having said that, geese at least (especially Canada geese Branta canadensis) sometimes sit in the sun with the wings hanging more to the sides than usual, thereby exposing the back to the sun. Various photos online labelled as showing ‘sunbathing’ ducks actually just shows ducks sitting in the sun, wings folded, in the normal resting pose. Swans sometimes swim along with one foot out of the water, toes stretched so that the webbing is fully exposed, and I’ve heard it said that this is to do with shedding heat, not collecting it. But, so far as I can tell, waterfowl don’t seem to stretch their wings out to ‘collect’ warmth – does anyone know otherwise? (if you’re thinking about the other members of Anseriformes – the screamers – let me give you a bit of advice and suggest that you don’t google ‘sunbathing screamer’). Since this article was first published in 2011, reports of sunbathing waterfowl have not come forward; indeed, an ornithologist specialising on waterfowl told me that they just don’t do it, so there.

Sunbathing Spectacled owl; image (c) Pook's Hill Lodge, Belize. Yes, owls of many kinds can and do sunbathe.

Many birds that you really wouldn’t regard as sunbathers apparently are, if only they get the chance. Do owls sunbathe? As this photo – taken at Pook’s Hill Lodge in Belize and passed via entomologist Max Blake – shows, indeed they do. This is a captive Spectacled owl Pulsatrix perspicillata, contorted into a fairly weird posture and with its eyes shut, but apparently still enjoying the sun. In fact, google will show you that of owls of assorted species belonging to most lineages are very happy to sunbathe, sometimes doing so with fully outstretched wings, raised feathers, lifted tails and often with a raised, back-curved neck that makes the head point skywards or even somewhat backwards.

Trumpeter hornbill at Birdworld, photo by Darren Naish. Much more on Asian hornbills to come at Tet Zoo sometime soon.

Because I tend to think of behaviours in a tree-based, phylogenetic context, I got wondering whether the same – or similar – postures are present in close relatives of owls, like mousebirds or the members of Picocoraciae. I’m not sure about mousebirds, but the sunbathing postures adopted by woodpeckers, bee-eaters and hornbills, at least, don’t seem especially unusual compared to other of other birds that perch and roost in trees.

Having mentioned perching, some birds will sunbathe while perched, fanning one or both of their wings while sitting well up off the ground. This Trumpeter hornbill Bycanistes bucinator spent a while with both of its wings fanned out to side.

Sunbathing Secretary bird at Birdworld, photographed in June 2011. Photo by Darren Naish.

On the subject of predatory birds, or raptors, if you will*, I was particularly happy to see this sunbathing Secretarybird Sagittarius serpentarius on its belly, wings fanning out to the side. It mostly kept both wings fanned out, but sometimes folded one wing away. Various hawk, eagle, vulture and condor species are well known for standing erect while facing the warmth of the sun and either holding their wings outstretched, or standing with their wings drooped to the sides in what’s known as a delta-winged posture. I’ve previously (Tet Zoo ver 2) used pictures of Andean condor Vultur gryphus and Lappet-faced vulture Torgos tracheliotos doing exactly this.

Andean condor (Vultur gryphus) (l), photo by Markus Bühler, and Lappet-faced vulture (Torgos tracheliotos) (r) in characteristic sunbathing postures.

Grey heron in delta-winged sunbathing posture. Photo by Lars Thomas.

Certain storks and herons also adopt delta-winged and spread-eagle poses (Curry-Lindahl 1970, Kahl 1971): the adjacent image (kindly provided by Lars Thomas) shows a Grey heron Ardea cinerea. Poses that involve holding the wings out don’t necessarily show that the bird is trying to warm itself: they might also be used when the bird is trying to lose heat, dry its feathers, show off to rivals, or shade its eggs or babies. Cormorants, pelicans, anhingas and others are well known for adopting spread-winged postures when they need to warm up, cool down, or dry their feathers.

* Some book says that owls are included in the ‘raptor’ concept, others dispute this and limit it to hawks, eagles, vultures and falcons. On this occasion I’ll gloss over the fact that the term ‘raptor’ belongs to a guild of neornithines, not to dromaeosaurids.

Grebes sunbathe in a distinctive posture where the rump is raised toward the sun while the wings and feathers on the back are held slightly raised. This helps expose a dark-skinned patch on the bird’s back that’s presumably good at absorbing heat (Storer et al. 1976). Even white- or pale-feathered mutant grebes retain this dark patch, suggesting that it’s physiologically important (Jehl 1985).

Mindanao bleeding-heart dove at Birdworld, photo by Darren Naish.

Based on my massive sample size (n = 2), it seems that pigeons like to recline on their sides during sunbathing, with the wing on the opposite site raised up such that the underwing is fully exposed to the sun. In fact, this is known to be typical for pigeons and doves (Hauser 1957, Nicolai 1962, Johnston 1965). The bird shown in the adjacent image – a Mindanao bleeding-heart dove Gallicolumba crinigera – stayed on its right side for a while, sometimes with its left wing raised and sometimes with the wing held loosely at its side. The Pink pigeon Nesoenas mayeri shown below also reclined with one wing raised (this time, reclining on its left side), but also fanned the right wing out flat on the ground. It fanned its tail feathers out at the same time.

Obliging Pink pigeon (Nesoenas mayeri), in two different sunbathing poses. Loved by everyone who reads Gerald Durrell. Photos by Darren Naish.

Sunbathing passerines of all kinds typically lie on their fronts, on the ground, their wings and tails spread out as much as possible. I photographed the sunbathing Greater necklacked laughingthrush Garrulax pectoralis and Snowy-crowned robin-chat Cossypha niveicapilla shown below; Michael O’Sullivan provided the image of the sunbathing Superb starling Lamprotornis superbus and Natee Himmapaan took the photo of the European starling Sturnus vulgaris. Note that the robin-chat has raised the feathers on its back and rump, and across much of its body in fact. Spread-eagled postures like this are seen widely across Telluraves – the great neognath clade that includes owls, woodpeckers, parrots and passerines.

Greater necklacked laughingthrush sunbathing, another photo taken at Birdworld. Photo by Darren Naish.

Snowy-crowned robin-chat at top (photo by Darren Naish) and Superb starling below (photo by Michael O’Sullivan).

The birds shown here are all in alert poses, even when lying recumbent. That is, their heads are up and they’re keeping an eye on the surroundings. It’s been noted in the literature that sunbathing is frequently risky: the birds are in a prone position and are relatively incautious and easy to approach. There are some indications that birds know this, in cases preventing (or trying to prevent) their mates from engaging in sunbathing (Kilham 1981). If birds are in a particularly safe location they’ll sometimes rest the head on the ground. A particularly neat image of a Peregrine Falco peregrinus doing exactly this – it was photographed on its nest, many metres above the ground – can be seen here.

Sunbathing European or Common starling (Sturnus vulgaris), photo by Natee Himmapaan.

Everyone familiar with birds knows that sunbathing behaviour is common, widespread and easy to spot, and various authors have wondered what function it might serve (e.g., Goodwin 1967, Kennedy 1968, Mueller 1972, Horsfall 1984). Some passerines have been seen sunbathing when already heat-stressed (they were gaping, projecting their tongues, and reclining in areas where the ambient temperatures were already higher than those generally thought to be ideal for small birds) (Blem & Blem 1992). This supports ideas that sunbathing is sometimes carried out for some function unrelated to the need to warm the skin or body: maybe it helps dislodge parasites, helps maintain feather condition (the easiest way to straighten a slightly damaged feather it to hold it in a stream of hot air), or helps ease the discomfort associated with moulting.

And in the spirit of All Yesterdays (go here for the Tet Zoo article, here to buy the book), I’ll finish by saying… where are all the sunbathing non-avian dinosaurs? (said with Aves used for the avialan crown). If you feel inspired to illustrate a sunbathing dinosaur (of any sort), feel free to send it along – if I get enough such images, I’ll do a follow-up article. For previous articles on other aspects of bird behaviour, see…

Refs – -

Blem, C. R. & Blem, L. B. 1992. Some observations of sunbathing in swallows. Journal of Field Ornithology 63, 53-56.

Curry-Lindahl, K. 1970. Spread-wing postures in Pelecaniformes and Ciconiiformes. The Auk 87, 371-372 .

Goodwin, D. 1967. Some possible functions of sun-bathing in birds. British Birds 60, 363-364.

Hauser, D. 1957. Some observations on sunbathing in birds. Wilson Bulletin 69, 78-90.

Horsfall, J. 1984. Sunbathing: is it for the birds? New Scientist 103 (1420), 28-31.

Jehl, J. R. 1985. Leucism in Eared Grebes in western North America. The Condor 87, 439-441.

Johnston, R. F. 1965. Sunbathing by birds. The Emu 64, 325-326.

Kahl, M. P. 1971. Spread-wing postures and their possible functions in the Ciconiidae. The Auk 88, 715-722.

Kilham, L. 1981. Sunbathing Vermilion-crowned flycatchers repulse mates. The Auk 98, 839.

Kennedy, R. J. 1968. The role of sunbathing in birds. British Birds 61, 320-332.

- .  1969. Sunbathing behaviour of birds. British Birds 62, 249-258

Mueller, H. C. 1972. Sunbathing in birds. Zeitschrift für Tierpsychologie 30, 253-258.

Nicolai, J. 1962. Uber Regen-, Sonnen- und Staubbaden bei Tauben (Columbidae). Journal of Ornithology 103, 125-139.

Simmons, K. E. L. 1986. The Sunning Behaviour of Birds. Short Run Press, Ltd., Exeter (UK).

Storer, R. W., Siegfried, W. R. & Kinahan, J. 1976. Sunbathing in grebes. Living Bird 15, 45-58.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. dusheck 8:54 pm 07/22/2013

    I think it IS known that birds need sunshine to synthesize vitamin D, just as we do.

    For reference, a California bird vet who researched this:
    “Birds secrete the precursor of vitamin D3 in the oils of their preen glands and spread it onto their feathers where it is photo activated by exposure to sunlight. They then either ingest the activated vitamin during further preening or absorb it directly through the skin. Vitamin D is critically important in calcium absorption in the intestine and its regulation in the circulatory system. A more widespread appreciation of this relationship could reduce the frequency of hypocalcemia in captive parrots.”

    http://www.forthebirdsdvm.com/pages/seeing-the-rain-forest-through-the-trees

    Link to this
  2. 2. Yodelling Cyclist 9:15 pm 07/22/2013

    Cool.

    Skulls, btw, just in case people have forgotten.

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  3. 3. Oenitholestes 9:41 pm 07/22/2013

    “Some book says that owls are included in the ‘raptor’ concept, others dispute this and limit it to hawks, eagles, vultures and falcons. On this occasion I’ll gloss over the fact that the term ‘raptor’ belongs to a guild of neornithines, not to dromaeosaurids.”

    I (and several others I know) generally use “raptor” to informally describe predatory birds, including owls, avisaurids and dromaeosaurids but excluding vultures. I’ve generally seen it defined as “Diurnal birds of prey with hooked bills and hooked claws” (According to Roger Tory Peterson)

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  4. 4. vdinets 10:26 pm 07/22/2013

    Do ratites sunbathe? Their feathers are probably too soft and dense to expose any skin, so if they do sunbathe, they probably do it for feather care (or something that happens on feathers), and if they don’t, it’s an indication that sunbathing has something to do with skin care.

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  5. 5. naishd 3:23 am 07/23/2013

    Thanks for comments.

    Oenitholestes (comment # 3) says “I (and several others I know) generally use “raptor” to informally describe predatory birds, including owls, avisaurids and dromaeosaurids but excluding vultures”.

    The fact that extant ‘raptors’ aren’t close relatives does make use of the term somewhat arbitrary, especially with mild disagreement as to whether owls should be included or not. But it’s always been used for hawk-like neognaths, so I don’t think extension to avisaurids or dromaeosaurids is appropriate. Vultures have been considered non-raptors by a few authors, but their inclusion within the guild is more normal (see, e.g., The Raptor Trust, the contents of Ferguson-Lee and Christidis’s book Raptors of the World, etc.).

    I’m always happy to agree with those who argue that language changes over time, but the established ornithological use of the term ‘raptor’ is still pretty consistent.

    Darren

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  6. 6. naishd 3:27 am 07/23/2013

    vdinets (comment # 4): I did check, and couldn’t find any records of sun-bathing in ratites, nor have I seen them doing it.

    Darren

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  7. 7. khwakaxoro 5:39 am 07/23/2013

    on the topic of birds with particular thermoregulatory needs, sunning behaviours in any penguin species?

    Found a couple of links for this in jackass penguins, on land:

    Frost, Siegfried and Burger 1976

    and at sea:

    Cooper 1977

    Though (knowing next to nothing about it) I would guess penguin feathers are rather peculiar,

    Link to this
  8. 8. BrianL 6:03 am 07/23/2013

    Rather peculiar given that ‘higher land birds’ generally seem to sunbathe, parrots don’t, I believe. Do we know if cuckoos, turacos or hoatzins sunbathe?

    Also, seeing sunbathing pigeons my mind started to wander towards sunbathing dodos and then I wondered: do we know if dodos (and solitaires) were capable of perching? My guess would be that they were, but I don’t recall it ever being mentioned anywhere these birds were discussed.

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  9. 9. naishd 7:05 am 07/23/2013

    BrianL (comment # 8): parrots and cuckoos do indeed sunbathe. Here are some sunbathing Neophema; here’s a sunbathing ground cuckoo.

    Dodos and solitaires were probably not capable perchers or climbers: their pedal phalanges aren’t especially short or stout, but their robust hindlimbs and weakly curved claws are definitely against it. Hopson (2001) included pedal digit data from Raphus in his analysis of phalangeal proportions and found it to plot in the ‘terrestrial’ section of morphospace. Having said that, other members of his ‘terrestrial’ section do roost and perch in trees.

    My review of Jo Parish’s dodo and solitaire book should be published soon. It’s in JVP.

    Darren

    Ref – -

    Hopson, J. A. 2001. Ecomorphology of avian and nonavian theropod phalangeal proportions: implications for the arboreal versus terrestrial origin of bird flight. In Gauthier, J. & Gall, L. F. (eds) New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom. Peabody Museum of Natural History, Yale University (New Haven), pp. 211-235.

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  10. 10. BrianL 7:22 am 07/23/2013

    @Darren: Okay, I clearly made a mistake there. Thanks for the reply about the perching abilities of dodos and solitaires. An interesting thing really, given that their ancestors undoubtedly were capable perchers as are their closest living relatives. I would like to point out that according to ‘Lost land of the dodo’ by Cheke and Hume,much of Mauritius upon being discovered was covered in very thick and tangled vegetation to the point where moving through was pretty difficult. The dodo may have stuck to more open terrain but perhaps it did have to negotiate fairly difficult terrain where being able to climb and perch, even if only poorly, would have been useful.

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  11. 11. naishd 7:25 am 07/23/2013

    Yeah, good point. Rock doves and ground hornbills are both in Hopson’s ‘terrestrial’ cluster, and – as you note – Goura and so on are capable perchers. The strongly reduced wings of dodos and solitaires might also have made it difficult for them to balance when on branches more than a few cm off the ground though…

    Darren

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  12. 12. glynyoung 9:19 am 07/23/2013

    I have never seen any wildfowl truly sunbathing. White-backed ducks (Thalassornis)however, can raise the feet up onto their back and extend their toes and webbing. The extended, black, feet presumably act like solar panels and absorb heat. Swans also do this at times and certainly WBD typically do it after sunrise so I assume that they are using the black surface to absorb heat after a night on cooling water and warming up to start the day. Maybe later in the day, in the African heat, WBD cool down this way but captive ones here in Jersey definitely seem to be warming up. The nearby trees are filled with ruffed-lemurs exposing their black chests to the rising sun even though they must feel its a waste of time most of the year!

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  13. 13. Crown House 5:02 pm 07/23/2013

    Hey, a quiz! I love quizes! So what shall I say, lets see… I’d say it’s either a juvenile caiman or a young crocodile, but probably not niloticus;)

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  14. 14. RaptorX 5:03 pm 07/23/2013

    @naishd (comment #6): I recall seeing a Cassowary at my local zoo quite a while back that was laying down in sunny patch of its enclosure with its head resting over its back (most similar to your picture of the Superb starling, but not quite). At first I thought it was sleeping, but it kept on opening its eyes and would shuffle its body around every once and a while. It looked to me like it was sunbathing, but I could be wrong.

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  15. 15. vdinets 10:20 pm 07/23/2013

    The thing is, if ratites don’t sunbathe, we can’t be so sure that non-avian dinosaurs did.

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  16. 16. vdinets 5:46 am 07/24/2013

    Although, on the other hand, crocodilians do sunbathe (I mean, for reasons other than warming up). If they can’t, they get algal growth on their backs and other problems.

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  17. 17. naishd 6:11 am 07/24/2013

    vdinets: you might be right (about lack of sunbathing in ratites = no sunbathing habit for avian common ancestor). However, it would be equally parsimonious to think that – if ratites are non-sunbathers – they have lost this habit, since it has to be assumed to be primitively present in Neognathae, the palaeognath sister-group. Maybe ratites don’t do it because of the unique body shape and small wings present in non-tinamou lineages (we’re now in a transitional phase, where the term ‘ratite’ is being used by some for ‘mostly big, flightless palaeognaths’ and by others for the clade that includes all of those taxa, with tinamous deeply nested within it).

    And, on the subject of tinamous, I’ve found one reference to sun-bathing behaviour in tinamous (on wikipedia’s tinamou article): given that it now seems (or…. we now know; take your pick) that tinamous are deeply nested within ratites, this further strengthens the view that flightless ratites have lost a sunbathing habit that was most likely present in their common ancestor.

    I recently completed a long article on the behaviour of fossil birds. Didn’t include a section on sunbathing behaviour… I wonder if I should have?

    Darren

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  18. 18. BrianL 6:15 am 07/24/2013

    I’ve also seen a cassowary sunbathing in Prague Zoo, come to think of it. Perhaps the deep black feathers of cassowaries make them just slightly more suitable for sunbathing than those of other ratites? Of course, ostrich males have black feathers but not as deeply black as those of cassowaries.

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  19. 19. Tayo Bethel 2:25 pm 07/24/2013

    Do petrels sunbathe?

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  20. 20. vdinets 7:38 pm 07/24/2013

    Tayo: fulmars do in colonies (per. obs. at Land’s End, Cornwall), and snow petrels sunbathe and snowbathe in the morning at the summits of South Georgia mountain peaks (I read it in a book written by the island’s only resident couple).

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  21. 21. BrianL 5:19 am 07/25/2013

    Does anyone know if Strisores of any kind sunbathe?

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  22. 22. Yodelling Cyclist 12:09 pm 07/25/2013

    Are there any tetrapods that will not sunbathe under any conditions? I’m thinking those which are either fossorial or cave dwelling, but are there any animals that have the ability to stand in the sun which won’t?

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  23. 23. Hai~Ren 4:34 am 07/28/2013

    I’ve lost count of the number of times I’ve had to brake or swerve while cycling to avoid sunbathing feral pigeons.

    Link to this
  24. 24. David Marjanović 9:38 am 07/28/2013

    Aaaaand that was 23. :-)

    Link to this

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