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 ﬂeshy 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.