I love turkeys, and here I specifically mean the so-called Wild turkey Meleagris gallopavo and its domestic variants, not the Ocellated turkey M. ocellata (though - don't get me wrong, Ocellated turkeys are great too). Herewith a brief look into the world of turkeys (part of it recycled from Tet Zoo ver 1)... involving a brief excursion on motmots and rooks. I was going to finish up on the whole pterosaur reproduction thing, but I can't. I'll explain why soon enough. [Composite below incorporates images from wikipedia and an original at far right].
Like so many birds, turkeys are ridiculously flamboyant and over-the-top in terms of their sexual ornamentation. Granted, this has been very much exaggerated in the domestic breeds, but it's still extreme in the original wild forms. Male turkeys - called stags* - display a distensible frontal process, or snood, fleshy polyp-like lumps called caruncles, and a dewlap that extends from the lower jaw to the neck. These structures are enlarged and flushed red in display, and the snood visibly extends in an excited bird. While displaying to a female or intimidating a rival a stag raises its body feathers. Males will also drag their remiges along the ground, wearing the tips off and creating a distinctive 'shuff-shuff' noise: at least, this occurs in domestic birds kept on concrete; I don't know how widespread it is in wild birds.
* UPDATE: or toms, gobblers or cocks.
The motmot's tail
I'm really interested in those cases where birds modify their plumage by way of behaviour, and this is a great example. Rooks Corvus frugilegus and motmots (Momotidae) are often alleged to be other good examples of this sort of thing, but they almost certainly aren't. The oft-made suggestion that behavioural feather modification occurs in motmots - supposedly as they tear off the barbs from either side of their rectrix tips - is not accurate (Wagner 1950, Murphy 2007). The barbs actually fall away naturally, leaving both distinctive 'tail wire' and 'racket tip' sections on the two central rectrices. These are present only in males and seem to be aerodynamically costly sexual signals (Murphy 2010).
The Rook's bare face
I suppose I should now explain the behavioural feather modification that some people think occurs in rooks. Rooks of the nominate subspecies have naked faces, bill-bases and throats, but they start their life with black bristles covering the nostril region and a fully feathered face and throat, as is typical for crows (and for other rooks: the face is not bare in the east Asian rook C. f. pastinator) [adjacent illustration, contrasting adult C. f. frugilegus with juvenile condition, from a 1976 book called The Illustrated Book of Nature: A Seasonal Guide to the Habitats of the British Isles. Artists aren't credited, but I think the birds were done by Peter Hayman]. Unlike most crows, rooks are probers that feed on seeds, worms and insect larvae, and they spend a lot of time jabbing their bills into soil. So some people say that this action causes the facial feathers to wear away, and it's this behaviour that explains the naked-faced condition. I can't find an explicit mention of this suggestion in the literature but I'm sure I read it somewhere at least once (I've also encountered it in conversation).
Alas, no. The feathers are moulted away at anywhere between 10 and 15 months of age (Dunnet et al. 1969): their loss does not depend on erosion caused by probing. A proportion of the modern rook population hardly ever probes for food anyway: an awful lot of these birds (especially those living around farms, suburban areas and wildlife parks) probably acquire all of their food by just picking it up, not by digging for it. If the bare-faced condition really were behaviour-dependent, we'd be seeing increasing numbers of adult rooks with fully feathered faces. I've only ever heard of one such individual (in addition, Dunnet et al. (1969) reported a year-old bird with a fully feathered face that produced and incubated a clutch, but it only had a fully feathered face because it was young, not because it retained the fully feathered condition long into adulthood).
While on the subject of aberrant rooks, there's the skeleton of a four-legged individual in the collections at Tring (NHM).
Turkeys can be real hot-heads
Back to turkeys... it figures that the caruncles, snood and wattle have evolved as display structures. Indeed some studies indicate that females prefer stags with the broadest heads and longest snoods. Buchholz (1995) linked the appearance of these structures with parasite loads (and thus fitness). The length of the snood is linked to testosterone levels, and studies employing turkey models that differ only in snood length show that real males are far more likely to risk stealing corn from a short-snooded replica turkey than a long-snooded one (Buchholz 1997). [A particularly flamboyant male turkey is shown here; image by Xuaxo, from wikipedia].
A reasonable prediction is that snoods, wattles and all that naked head skin might make the birds prone to overheating when exposed for a time to the hot sun. And indeed some work suggests that overheating is a problem for the birds at times. Males seem to suffer more from heat stress than females do: they hide in the shade on hot days more than females do, and also pant more and are less keen to flee from people on sunny days than females are. It's also been shown that exposure to direct sunlight for extended periods can reduce male fertility by about 10% in domestic bronze turkeys, so sitting in the sun on a hot day is clearly not a good idea if you're a turkey. Buchholz (1996) looked at this area but noted that more study of wild turkeys was needed.
This was a very brief look at but a small aspect of turkey behaviour and biology (and the motmots and rooks proved something of a worthy distraction). Galliforms - gamebirds - have yet to receive adequate coverage on Tet Zoo. I really want to get round to writing about them in depth some time. And some day I will!!!
For previous Tet Zoo posts on gamebirds, and on weird/extravagant plumage, see...
- Why do some owls have ear tufts?
- The detachable tails of pigeons
- Perhaps the weirdest chicks of all
- Fish owls in reverse
- Yes, it was a kiwi
- How to prevent cannibalism in pheasants
- The Great bustard returns
- The Mesozoic birds with weird, plastic-strip-style tail
- Condors and vultures: their postures, their 'bald heads' and their sheer ecological importance
Refs - -
Buchholz, R. 1995. Female choice, parasite load and male ornamentation in the wild Turkey. Animal Behaviour 50, 929-943.
- . 1996. Thermoregulatory role of the unfeathered head and neck in male wild turkeys. The Auk 113, 310-318.
- . 1997. Male dominance and variation in ï¬eshy head ornamentation in Wild turkeys. Journal of Avian Biology 28, 223-230.
Dunnet, G. M., Fordham, R. A. & Patterson, I. J. 1969. Ecological studies of the Rook (Corvus frugilegus L.) in north-east Scotland. Proportion and distribution of young in the population. Journal of Applied Ecology 6, 459-473.
Murphy, T. G. 2007. Lack of melanized keratin and barbs that fall off: how the racketed tail of the turquoise-browed motmot Eumomota superciliosa is formed. Journal of Avian Biology 38, 139-143.
Murphy, T. (2009). Tail-racket removal increases hematocrit in male Turquoise-browed Motmots (Eumomota superciliosa) Journal of Ornithology, 151 (1), 241-245 DOI: 10.1007/s10336-009-0449-4
Wagner, H. O. 1950. Observations on the racquet-tips of the motmot's tail. The Auk 67, 387-389.
Great article, and an important point to consider in dino reconstructions... who knows what wonderful (or disgusting) features were lost during fossilization? Can you imagine... Can your heart take up... the harrowing possibility of SAUROPODS WITH SNOODS?!?
"Stags"? Surely, male turkeys are called toms.
It seems to be some sort of British lingual imperialism . On a serious note, what's the significance of turkey beards on top of all the other fancy ornamentation a tom has?
Male turkeys also get called gobblers or cocks. I hadn't realised that 'stag' was exclusive to the UK, but it seems it is (I honestly just thought - from the literature - that it was the 'correct' term).
There was supposed to be a fake html tag expressing sarcasm in my comment above, which previewed correctly but is now invisible. It was not intended as a serious complaint. Curiously, as a North American I had never before heard 'stag' used to describe a male turkey. I don't think the term is commonly used for any of our deer, either.
I just had a flock of turkeys visit my bird feeder for the first time ever three days ago. I was only slightly surprised when one hopped into a tree to get at a suet cake two meters up.
"I love turkeys, and here I specifically mean the so-called Wild turkey Meleagris gallopavo and its domestic variants, not the Ocellated turkey M. ocellata (though - don't get me wrong, Ocellated turkeys are great too)."
This may be the single greatest opening sentence of any blog entry ever. It's the "don't get me wrong" that does it -- as though Darren was brought up short by the horrible realisation that he might be inadvertently slighting the ocellated-turkey-loving segment of his audience.
Ocellated turkeys are so much cooler than their northern cousins; they have all the same stuff, but in technicolor (though they're both pretty colorful if you look closely). If your twitching ever leads you to Belize, I recommend Chan Chich, where the ocellated turkeys are extremely common. Motmots are there too, though oddly enough no rooks.
There's nothing wrong with galliforms, though they are the less interesting half of Galloanserae. Have you ever discussed megapodes?
Interesting stuff. I wasn't away juvenile rooks kept their facial feathers so long. I shall take a closer look next time I see a 'carrion crow' among the rooks
Megapodes, you say? (comment 7). HA! All will become clear in a short while... Or, to use non-code: no, I haven't written about them on Tet Zoo, but I've just been reading and writing about them quite a lot. Chickens too, seriously.
And so to the ever-popular subject of how stupid turkeys are. I quote from Wood (1982), the fabulous Guinness Book of Animal Facts & Feats, 3rd edition, which everyone should own. From page 89:
The question of the 'dimmest' bird, however, is much easier to resolve, and one needs to look no further than the domestic turkey (Meleagris gallopavo) for this title. On one occasion a farmer left an empty barrel in his yard. Six of his best turkeys promptly scrambed into it, piled up one on top of the other and died of suffocation because none had the sense to get out. Other breeders have known turkeys to stand out in the open during a heavy downpour and be drowned because they were not intelligent enough to walk a few yards to their hutches. Each year thousands of turkeys freeze to death on cold nights because the stubbornly refuse to seek refuge in their warm sleeping quarters, and some turkeys are so retarded [sic] that they even have to be persuaded to eat. Some farmers rear chickens alongside turkeys in the hope that the turkeys will copy the actions of their brighter companions, but this is generally wishful thinking. Turkeys are also great panickers, and on one occasion more than 13,000 being fattened for Christmas were trampled to death on a poultry ranch in Corning, California, USA where a low-flying jet suddenly flew over. There are even reports of turkeys being frightened to death by pieces of paper fluttering in front of their paths.
All this is fascinating (and, let's admit it, pretty funny). Does anyone know how much of this is documented in scientific literature? Wood is a pretty serious scientist, but the Guinness book is definitely written for a popular audience.
Those "stupid turkey" stories are only funny because it is assumed the turkey is so stupid it allows itself to get killed. What if the turkey is so clever that it becomes unbearably melancholy in its captivity and prefers to die in ridiculous suicide pacts rather than end up on the table in front of bloated Americans?
Darren, I saw those couple of articles, really neat, but they could have pushed the envelope weirdness even further... I also used a similar trick in my hypothetical sauropod sophont, it had weird nose sacs, a bagpipe-like throat sac, and wattles, snoods, etc. http://svpow.wordpress.com/2010/06/17/i-for-one-welcome-our-new-sauropo…
This 'look how stupid turkeys are' stuff frequently crops up whenever they're mentioned, but it's all based on anecdote, not on empirical work. The quick retort that usually follows is that these tales are exaggerated and that turkeys are no dumber than any other cerebrally 'average' bird. Claims that they drown when left out in heavy rain, or deliberately pile into barrels and suffocate to death, or stampede into a panic when frightened, might be true, but if so I bet that many other animals would do no better when in the same situation.
There is a bit of data on EQ across birds, and turkeys actually come out of it reasonably well. A 5kg turkey has a brain that weighs about 7g (1.4% body mass) [WRONG: see comments below]. In a 550g chicken, the brain is 2.7g (0.5% body mass) and, in a 3.2kg goose, the brain weighs 11.3g (0.35% body mass). In an Emperor penguin of 28kg, the brain weighs 46.2g (0.16% of body mass). I could compile other data, but the point is that turkeys are not small-brained, and not obviously stupid/unintelligent, compared to other galloanseraens, or indeed to other birds.
In contrast, a 'big-brained' bird like a parakeet with a mass of 75g has a brain 2.9g in mass (3.8% body mass). I took the data from...
Roth, T., Lesku, J. A., Almaner, C. J. & Lima, S. L. 2006. A phylogenetic analysis of the correlates of sleep in birds. Journal of Sleep Research 15, 395â402.
As usual, it's not unlikely that I screwed up on the calculations.
As usual, it's not unlikely that I screwed up on the calculations.
'fraid so :-) You slipped a decimal place. A 7g brain in a 5kg bird represents 0.14% of body mass, not 1.4%. So turkeys are in fact ten times as dumb as you portray them here. Har har.
The broader point is the EQ is of course not just ratio of brain mass to body mass, but ratio of brain mass to the brain mass that would be expected in an animal of that body mass, based on the best-fit allometric line. In general, larger animals have proportionally smaller smallers brains than smaller ones, which is in keeping with your chicken/goose/penguin data. The turkey brain-mass is rather smaller than would be expected, but not by as much as raw brain:body mass ratios would suggest.
Dammit. Stupid numbers. But you can see that a turkey is similar in relative brain size to an Emperor penguin, and yet nobody ever says how dumb penguins are. Then again, that's likely because people are more familiar with turkey behaviour than that of penguins.
Sorry to go on about this, but these figures do not indicate similar relative brain size in turkeys and penguins (except in the simple mass ratio sense). The allometric constant for brain size is usually given as 2/3, which means a 28 kg penguin weighing 28/5 = 5.6 times as much as as a 5 kg turkey would be expected to have a brain 5.6^(2/3) = 3.15 times as massive as that of the turkey. Based on the 7 g brain of the turkey, that suggests that an equally "intelligent" Emperor penguin would be expected to have a 22 g brain. In fact it weight more than twice that (46.2 g), so its EQ is more than twice that of the turkey.
Ok, whatever. I shouldn't have brought it up in the first place. Anyway, as you know, EQ doesn't definitely tell you anything about 'intelligence'.
Wood is a pretty serious scientist, but the Guinness book is definitely written for a popular audience.
Wait, isn't this the same guy who claimed that Ensatina could shoot venom or some shit?
This 'look how stupid turkeys are' stuff frequently crops up whenever they're mentioned, but it's all based on anecdote, not on empirical work...% body mass
bah. Brain size scales to body size allometrically; a raw ratio means nothing.
As MP Taylor points out in the very next comment.
And I can't find the reference from which I pulled this fact, but my pre-Thanksgiving lecture notes on the biology of turkeys includes the claim that domestic turkeys have brains that are 30% smaller (in absolute mass) than those of their wild conspecifics (despite the smaller body size of wild turkeys).
[While I'm at it, I also noted from someplace that domestic turkeys have systolic blood pressures of 300-400 mm Hg,and that up to 10% of some flocks die of aortic rupture.]
[While I'm at it, I also noted from someplace that domestic turkeys have systolic blood pressures of 300-400 mm Hg,and that up to 10% of some flocks die of aortic rupture.]
That's pretty darned interesting, because one of the papers that Seymour and Lillywhite used for raw data for their sauropod blood pressure paper listed an unusually high ventricular wall stress in turkeys.
Note to self: never write about anything involving ratios, percentages, relative proportions, quotas, quotients, or numbers in general. They only cause pain and should be avoided at all costs.
But that thing about blood pressure is pretty neat...
[PS - the squirting Ensatina claim comes from Mark Carwardine's Guinness Book of Animal Records, not from Wood's Guinness Book of Animal Facts & Feats. I never did find out for sure, but I wonder if Carwardine somehow got Ensatina confused with the gekkotan Diplodactylus.]
If you're going on about penguin brains, you could at least link to the Monty Python sketch.
"The first thing that Dr Kramer came up with was that the penguin has a much smaller brain than the man. This postulate formed the fundamental basis of all his thinking and remained with him until his death. Now we've taken this theory one stage further. If we increase the size of the penguin until it is the same height as the man and then compare the relative brain sizes, we now find that the penguin's brain is still smaller. But, and this is the point, it is larger than it was. For a penguin to have the same size of brain as a man the penguin would have to be over sixty-six feet high." And so on.
Who says people are more familiar with turkeys? That would depend on where you live. Penguins are a lot more common in my neck of the woods (Melbourne, Australia).
Penguins are closer I suppose. But we've got our own (completely unrelated) turkeys in Oz (brush turkey/bush turkey). Come to think of it, a north american turkey is kinda like a minature Cassowary as well. :)
You didn't mention that male turkeys change their skin color (at least on their heads)
I don't know how this works, but i've seen it. I don't think the vibrant blues and reds seen in the last picture are what the turkey "normally" looks like. At least in my limited experience those vivid colors appear when the turkey is showing off.
Is this the result of blood, or chromatophores?
Also as an American i've only heard the males described as "Toms"
On bird skin colors, I read in the Handbook of the Birds of the World that the bright greens and blues in Philepitta face wattles are caused by ordered layers/fibres of collagen below the skin. Does anybody know of a study on other examples? like the above mentioned cassowary, or turkeys or any bird with brightly colored skin. No blue pigments exist in terrestrial tetrapods (not in birds at least), so blue hues must be produced by scattering or other optical phenomenon.
nobody ever says how dumb penguins are
Yes they do. There's a popular 'dumb penguin' story about how RAF pilots on the falcons fly over penguin nesting beaches and all the penguins watch the plane going over until they all fall over backwards.
And yes it's all true
Perhaps the way most galloanserans and penguins always look slightly taken aback probably has something to do with it. Mind you, I challenge anyone to come up with a popular 'dumb swan' story.
@farandfew, I suspect that's partly because swans have a nasty habit of beating the living hell out of people every so often. They may be dumb, but no one wants to say it to their face.
I hadn't heard any of those penguin stories, good to have some people in the audience that actually runs into them every so often! Relatedly, from the US I've never heard a male turkey called a stag, but regularly hear it in reference to deer.
the face is not bare in the east Asian rook C. f. pastinator
my pre-Thanksgiving lecture notes on the biology of turkeys includes the claim that domestic turkeys have brains that are 30% smaller (in absolute mass) than those of their wild conspecifics (despite the smaller body size of wild turkeys)
So domesticated birds, too, have smaller brains than their wild ancestral forms? That's interesting, because relative brain size reduction is a pretty well-documented phenomenon in domesticated mammals* (e.g., Kruska, 2005).
* Note that we should not therefore automatically assume that domesticated animals are less 'intelligent' (however we may choose to define that term) than their wild relatives (e.g., Lewejohann et al., 2010).
Kruska, D.C.T. 2005. On the evolutionary significance of encephalization in some eutherian mammals: effects of adaptive radiation, domestication, and feralization. Brain, Behavior and Evolution 65, 73-108.
Lewejohann, L., Pickel, T., Sachser, N. & Kaiser, S. 2010. Wild genius - domestic fool? Spatial learning abilities of wild and domestic guinea pigs. Frontiers in Zoology 7:9.
...and I guess it was inevitable that a post about turkeys should attract spambots that (apparently) are from Turkey. (By the way, Darren, there is also a spam comment in the previous pterosaur post thread that you haven't yet deleted.)
Regards the four legged rook at Tring: does it have four legs as well as wings? If so, are both pairs of hindlimbs the same size?
Thanks as always for comments - I've now deleted those spam messages (both on this article and the previous pterosaur one). Goddam spammers. Thanks for the heads-up. Other responses...
Colour change in turkeys (comment 24): I did at least say that males flush their skin red during display.
Facial skin colour in birds (comment 25): there's a really nice paper on this by Prum & Torres (2003). Most birds with brightly coloured head skin possess "quasi-ordered arrays of parallel collagen fibres", typically with a layer of melanin granules beneath. While it was typically assumed that Tyndall scattering (or Rayleigh scattering) was responsible for the blue and green face, bill and foot colours seen in birds, Prum & Torres (2003) (building on earlier work by Prum et al. (1994)) showed that "coherent scattering from hexagonally organized arrays of parallel collagen fibres in the dermis" explains the skin colour of more than 50 avian lineages: the skin of these birds is thus 'structurally coloured', rather than just pigment coloured. At the moment, the distribution of structurally coloured skin in birds seems pretty random, indicating that it has evolved convergently on a massive scale. Melanin granules aren't always present: they're absent in some cotingas and antbirds, and are also not present in birds with carotenoid-pigmented skin, like yellow-faced toucans. A combination of structural coloration and pigmented skin is not uncommon, being seen in toucans, pheasants and trogons, among others. A pretty fascinating topic that will become more so as we learn more about the integument of extinct animals. Oh, and Philepitta castanea is unique (so far) in that its collagen fibres are not 'quasi-ordered', but arranged in an exceptionally ordered, hexagonal array. If any of this interests you, do track down a copy of Prum & Torres (2003).
Penguins (comment 26): the story about how penguins fall over when watching overhead jets (I recall this story being told during the Falklands War) seems to be a sort of myth. I don't know if youâre aware of Stephen Fry's BBC TV series QI (QI = 'Quite Interesting'), but he said in one episode that it was definitely false. I've never been around penguins when a plane has flown overhead so can neither confirm or deny.
Marc (comment 30): the rook in question has six limbs, four of which are hindlegs. All the legs are the same size, and grouped in pairs. I'm pretty sure the specimen was discussed in a brief paper somewhere. I have one very bad photo if you're interested.
Refs - -
Prum, R. O., Morrison, R. L. & Ten Eyck, G. R. 1994. Structural color production by constructive reflection from ordered collagen arrays in a bird (Philepitta castanea: Eurylaimidae). Journal of Morphology 222, 61-72.
- . & Torres, R. 2003. Structural colouration of avian skin: convergent evolution of coherently scattering dermal collagen arrays. The Journal of Experimental Biology 206, 2409-2429.
I've actually been watching a family of rooks on the University of Aberdeen campus, which seem to have an aberrant "pied" colouring with white feathers their wings. The first rook with white on it appeared about 2 1/2 years ago, with only scattered white feathers (and I thought at first it might have been the result of scarring or some other non-genetic damage), but last spring there were two, one of which had much considerably more white, and currently there are at least four and possibly five (one of them is generally resident in a high-walled garden and is hard to get a good look at, so it could be a new one or could be one of the four I know I've seen). One of these has quite broad, symmetrical and well-defined bands of white on the underside of the wings and scattered white feathers on the top of the wings. The white feather pattern is slightly different on each individual; but aside from the white patterns, they are absolutely typical rooks.
I don't suppose you know of any resources on colour variations in rooks, do you?
Penguins are so dumb that they think the antarctic is where you find really cold ants.
The straight dope's take on turkey's drowning in the rain:
I like ratios! They're so simple and yet often can encapsulate fundamental biological truths. It's fun when I can understand a quantitative description of biological systems through some ratios and a best-fit line :)
Anywhoo, nice post and discussion.
As far as variant plumages go - white feathering on an otherwise black bird may be due to dietary factors or disease affecting developing feathers, but it can also be due to genetic factors. With several similar birds in the same area my bet is on genetics - I expect they are related. European blackbirds are especially prone to showing this - I have seen several examples. On a related topic, in many birds with naturally green feathers captive populations often produce yellow or blue variants, depending on whether the yellow or blue in the normal form is not produced. I am not sure if there were any green-feathered dinosaurs, but if there were it is a pretty good bet that there were occasional yellow or bright blue ones..
To clarify the skin color thing: all blues in birds, as far as I know, are structural colors, i.e. not due to pigment but to those arrays of collagen or keratin that scatter certain wavelengths. As far as I know, too, all reds in skin are due to blood, though that obviously isn't so for feather colors. Greens in skin are combinations of yellow pigment with structural blues.
Anyway, tragopans are much cooler than turkeys in that regard.
Yes, I think all blue skin in birds is indeed structural... though the structural mechanism explaining facial colour in the thamnophilids Gymnopithys and Rhegmatorhina remains enigmatic, since their dermal collagen arrays are apparently too small (in the nanostructural sense) to produce the light blue hues that are present (their collagen arrays should be transparent or produce something in the far ultraviolet). Weird.
Where I live (Central Ontario) wild turkeys were extirpated and since re-introduced. It has been great watching them return to the area, seeing them feed in the cornfields and flocks roosting in trees. I have always wondered how their naked heads do not freeze (it was -42 here a couple of weeks ago). I imagine they sleep with their heads under their wings, but during the day foraging, it must get quite cold.
Here in Texas, male turkeys are called gobblers or toms. In Spanish, pavo is a tame turkey, guajolote is a wild turkey. Present day domestic turkeys are so breast heavy they cannot fly. Does this increase in breast meat explain the relative decrease in brain/body ratio? First time, at @ 12 years old, I fixed supper for myself, I had fried wild turkey breast and cream gravy. It was so good!