Inspired by comments made following the emu dissection article from Monday, I got thinking about elongate tracheae in birds. As we'll see, this subject is fertile ground if you like serious weirdness and spectacular extremes [Trumpet manucodes shown here, from wikipedia.. all will become clear]. Before we get to that serious weirdness and those spectacular extremes, a bit of basic anatomy...
The trachea - or windpipe - is, as I'm sure you already know given that you've got one, a tube that extends along the ventral surface of the neck from the larynx to the lungs [singular: trachea, plural: tracheae. Thanks David]. While the tetrapod larynx normally contains vocal chords used in sound production, it does not contain vocal chords in birds and hence has long been thought to have no role in vocalisation at all. Recent work has shown that this is not true, and that a significant amount of laryngeal movement in birds helps them to control their vocalisations. In fact some birds (like crowing roosters) descend the larynx during vocalisation: huh, once upon a time, laryngeal descent was thought unique to humans [for more on laryngeal descent in non-humans, see the Fallow deer article]. Incidentally, the role of laryngeal movement in avian vocalisation was initially predicted on the basis of dissection data (Homberger 1986, 1999) and, about 20 years later, confirmed by cineradiography.
While the larynx does play a role in vocalisation after all, the syrinx (located at the base of the trachea and deep within the chest) is more important. It's a pretty complicated structure, involving muscles, membranes and internal foramina. There's a lot that could be said about it (it's tremendously variable), so I'll leave well alone for now. Incidentally, syringeal musculature is absent in some birds (namely some storks), so the only noises they make are 'mechanical' ones like bill-clattering. Posterior to the syrinx, the trachea bifurcates into the two primary bronchi, and these then lead into the lungs. Cartilaginous tracheal rings are arranged along the trachea's length and keep it stiff and open all the time [Trumpeter swan trachea and sternum shown here, from Banko (1960). Read on...].
Hypertrophied trachea in swans and cranes, and 'problems' of dead space and storage
In the vast majority of birds, the trachea is, apart from the syrinx, pretty simple. However, several groups have evolved incredibly elongate tracheae where extra loops, hoops and other deviations increase its length, sometimes to an utterly ridiculous degree. The most familiar birds with tracheal looping are swans: tracheal length is variable in the four species that exhibit it, but in all of them the trachea forms an S-shaped loop at its base. In species without an elongate tracheal loop, like the Black swan Cygnus atratus, the base of the trachea fits into the space between the furcula and the anterior edge of the sternum. In contrast, the extremely long loop of the Trumpeter swan C. buccinator invades the chest cavity and is attached to the medial (inner) surface of the sternum, forming an obvious tube on the sternal surface (Banko 1960). You can see it in the photo below: the trachea invades the sternum at its anterior end and then forms the bulbous mass you can see on the upper surface.
The Trumpeter swan trachea is more than three times larger in volume than expected for a bird of its size (Hinds & Calder 1971), and having a trachea of this length means that the birds have to cope with a tremendous dead space (dead space = the amount of air that has to be shunted out of the way before the animal can take in a new breath). Here it would be all too easy to go off on a tangent and talk about air-sacs and avian respiration, and I regret I can't do that... I will say, however, that dead space is probably not as much of a problem for birds as it is for mammals and it's probably relatively easy for birds (with their extensive air sac system) to move large volumes of air around (Clench 1978, p. 428). Must resist mention of sauropod dinosaurs - - err, dammit.
Very long tracheal loops are also present in cranes. Having said that the condition in swans is most familiar, I should note that this could instead be said for cranes: Kaiser Friedrich II described crane tracheae in 1250, the French naturalist Pierre Bollonius was writing about tracheal elongation in cranes again during the 1500s, and crane tracheal morphology was illustrated by V. Coiter in 1575 (Johnsgard 1983, Fitch 1999). In some cranes, the tracheal loop comes into contact with the anterior margin of the sternum and the sternum's leading edge is strongly recessed to receive it [see adjacent diagrams, from Johnsgard (1983)]. In forms with longer tracheal loops, the trachea properly invades the body of the sternum, and in the species with the very longest tracheae (like Eurasian cranes Grus grus and Whooping cranes G. americana) the entire length of the sternum is occupied by tracheal looping: the loops double-up on themselves, forming a complex coil. In the Japanese crane G. japonicus, the trachea can be 1.6 m long in total (Johnsgard 1983). Crane sterna, and their associated tracheae, are shown in the adjacent image [from Johnsgard (1983)]. The more 'extreme' European crane and Whooping crane are shown at the bottom.
Elongate tracheae are also present in magpie geese, in chachalacas and various other cracids, in ptarmigans, capercaillies and some guineafowl, in some spoonbills, in painted snipe, and in limpkins. The presence of an elongate trachea in the Capercaillie Tetrao urogallus is particularly interesting given the claim that this is one of very few birds that can produce infrasound (Moss & Lockie 1978). However, later testing showed that capercaillie calls did not include an infrasonic component after all: however, the 'flutter jumps' that these large birds use as part of their displays do create infrasound (Lieser et al. 2005). At the moment the only confirmed infrasonic birds are cassowaries (and they don't have elongate tracheae). Thanks to exceptionally preserved specimens, one of which was discovered with an in-situ trachea [shown here, after Worthy], we know that two moa - Euryapteryx and Emeus - had very long, looping tracheae (Worthy & Holdaway 2002).
Where do birds store their elongate tracheae? We've already seen that the tracheae of swans and cranes are either coiled up against, or even upon or within, the sternum. In the guineafowl with looped tracheae (two members of the genus Guttera, most notably the Crested guineafowl G. pucherani), the loop is fitted away inside the hollow furcula (Chapin 1932, Frith 1994). The European spoonbill Platalea leucorodia and Yellow-billed stork Mycteria ibis (apparently) are unusual in that the coiled tracheal loop is within the thoracic cavity: that is, medial to the clavicles and sternum, though not in close association with the sternum as is the case in swans. In a bizarre and fascinating case of convergence, the elongate moa trachea was also intrathoracic (Worthy & Holdaway 2003). It's more normal, however, for the tracheal loop or loops to be positioned ventral to the sternum, and be tucked up against the pectoral muscles. This is the case in Magpie geese Anseranas semipalmata, cracids, Painted snipe Rostratula benghalensis, and in the birds-of-paradise that have long tracheae (Frith 1994). And I've left birds-of-paradise to last. Why? Because their tracheal loops are perhaps the most extreme of all. They. Are. Ridiculous.
Most ridiculous of all: birds-of-paradise
Two kinds of birds-of-paradise have looped tracheae: the Trumpet bird or Trumpet manucode Phonygammus keraudrenii and the manucodes proper (Manucodia). It is probable that, among birds-of-paradise, the long tracheae possessed by these two taxa evolved only once, as Phonygammus and Manucodia appear to be sister-taxa (in fact, some authors include Phonygammus within Manucodia). The elongate Trumpet bird trachea was first reported in 1826, figured and discussed a few times in the late 1800s, and reviewed comprehensively by Clench (1978): it really has to be seen to be believed. Aaaand, here it is... [as represented by three specimens, from Clench (1978)]...
It is extremely variable ontogenetically, sexually, and between populations, but - at its most extreme - consists of five coils that form a spiral on the animal's ventral surface. The trachea descends posteroventrally on the bird's left side, extends posteriorly all the way to the cloaca, then curves to the right before travelling anteriorly to form the next loop.
The tracheal looping is similarly ridiculous in the other manucodes, but there aren't as many spirals. However, the trachea extends even further posteroventrally in the manucodes than it does in the Trumpet bird: Clench (1978) figures one specimen [shown here] where the trachea loops upwards near the cloaca, and then extends on the side of the animal's right thigh before looping back to the underside!
Why have super-long trachea?
So - - why do these birds have these super-long, looping or coiled tracheae? While it has been suggested that elongate tracheae might have a role in respiration or physiology (see Fitch 1999 for review), it has generally been thought that elongate, coiled tracheae allow their owners to make especially loud, resonant noises, and it's notable that the birds we've just been looking at are the ones that create some of the loudest, most powerful, furthest-carrying noises within Aves. Trumpeter swans, Whooping cranes and Trumpet birds are the noisiest members of their respective groups, and exhibit the most complicated and elongate tracheae of their respective groups. I think we can safely infer that extinct birds with long, looping tracheae - like those moa - made loud, striking calls too.
Fitch (1999) argued that the calls made by birds with elongate tracheae are disproportionately loud compared to the size of the bird: therefore, elongate tracheae do not just permit particularly deep or loud calls, but also lower the formant frequencies and hence function in acoustic size exaggeration. This is a neat trick, as larger body size (or, the impression of large body size) is advantageous for sexual competition and advertisement, and may also play a role in intimidating predators. Also notable is that birds with long, looped trachea are all relatively large, and at least some of them nest in areas with dense vegetation where visibility is restricted (Fitch 1999).
Like a trombone - or like a violin?
Do the tracheal loops act in the same manner as the tubes of a trombone? This is what most authors have assumed, but Gaunt et al. (1987) argued that - in cranes - tracheal coiling made no difference to call volume. Instead, they proposed the novel idea that the integration of the tracheal loops with the sternum allows the entire apparatus to function like a stringed instrument. Perhaps, they proposed, the entire surface of the large sternum resonates during a call. Its vibrations are then, they proposed, amplified by the internal air sac system. I have no idea whether this hypothesis is reasonable or not and am unaware of any follow-up work. The idea that big birds might use their enormous bony sterna, super-long tracheae and extensive air sac systems to make particularly loud noises is pretty exciting, and must be one of the most incredible cases of exaptation among Tetrapoda... if correct. Gaunt et al. (1987) noted that, if they are correct, then birds like cranes function more like violins than trombones [Eurasian crane shown here, from wikipedia].
Incidentally, there is a possible cost to having large, complex tracheae: they might be especially prone to fungal infections (Souza & Degernes 2005).
While writing this piece I worked hard to resist all the diversions that came along: the avian larynx and syrinx, the syringeal bullae present in some waterfowl, the expanded (but not long) tracheae of umbrellabirds and other cotingas, the dead space problem and how it might link to pneumaticity, and so much more. In part I succeeded, but in part I didn't. This is a very neat area and it's really got me inspired, and I hope you enjoyed it too.
Refs - -
Banko, W. E. 1960. The Trumpeter Swan. North American Fauna Series No. 63. US Fish and Wildlife Service, Washington, D.C.
Chapin, J. P. 1932. The birds of the Belgian Congo. Volume 1. Bulletin of the American Museum of Natural History 65, 1-756.
Clench, M. H. 1978. Tracheal elongation in birds-of-paradise. The Condor 80, 423-430.
Fitch, W. T. 1999. Acoustic exaggeration of size in birds via tracheal elongation: comparative and theoretical analyses. Journal of Zoology 248, 31-48.
Frith, C. B. 1994. Adaptive significance of tracheal elongation in manucodes (Paradisaeidae). The Condor 96, 552-555.
Gaunt, A. S., Gaunt, S. L. L., Prange, H. D. & Wasser, J. S. 1987. The effects of tracheal coiling on the vocalizations of cranes (Aves; Gruidae). Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 161, 43-58.
Hinds, D. S. & Calder, W. A. 1971. Tracheal dead space in the respiration of birds. Evolution 25, 429-440.
Homberger, D. G. 1986. The lingual apparatus of the African grey parrot Psittacus erithacusLinné (Aves: Psittacidae): description and theoretical mechanical analysis. Ornithological Monographs 39, 1-233.
- . 1999. The avian tongue and larynx: multiple functions in nutrition and vocalization. In Adams, N. & Slotow, R. (eds) Proceedings of the 22nd International Ornithological Congress,University of Natal, Durban, South Africa. BirdLife (Johannesburg), pp. 94-113.
Johnsgard, P. A. 1983. Cranes of the World. Croom Helm, London.
Lieser, M., Berthold, P. & Manley, G. A. 2005. Infrasound in the capercaillie Tetrao urogallus. Journal of Ornithology 146, 395-398.
Moss, R. & Lockie, I. 1978. Infrasonic components in the song of the capercaillie Tetrao urogallus. Ibis 121, 95-97.
Souza, M. J & Degernes, L. A. 2005. Mortality due to aspergillosis in wild swans in northwest Washington State, 2000-02. Journal of Avian Medicine and Surgery 19, 98-106.
Worthy, T. H., Holdaway, R. N. 2002. The Lost World of the Moa. Indiana University Press, Bloomington, Indiana.
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This is a great post to include in tomorrow's I and the Bird carnival.
Wow! What a marvellous post! Lots of new information to digest. I have a few comments/questions though:
That's true for white storks Ciconia ciconia, but is it really true for all other storks as well? I'm under the impression that the black stork C. nigra, at least, can make some sounds; is that not correct?
Interesting; how long is it in the mute swan Cygnus olor (which isn't really 'mute', but still much less vocal than, e.g., C. cygnus or C. buccinator)?
Huh? I better take a look at Fitch's paper, because that sounds wrong to me, at least as far as swan and crane behaviour is concerned. Most swan species do not usually nest in "dense vegetation" but instead very openly. They are very loud and very conspicuous, and don't try to hide at all. Most cranes don't behave in a particularly cryptic way either (at least not in areas where they aren't hunted by people) and seem to rather prefer habitats with good visibility.
Singular: trachea, plural: tracheae. There is no Latin or Greek word in -a that is identical in singular and plural.
Thanks for those comments: I've just made a few corrections.
"This is a very neat area and it's really got me inspired, and I hope you enjoyed it too."
I can't speak for everyone, but I think they'd probably agree that we love it when you get a bee in your bonnet (or whatever the tetrapodal equivalent of that is!).
Response to Dartian on tracheal elongation and the habit of nesting in densely vegetated areas: Fitch (1999, p. 44) said 'Although cranes are typically large birds that are clearly visible over the vegetation in the open grasslands and steppes that they frequent while wintering, many or most cranes build nests in densely overgrown areas, and visual isolation appears crucial for nesting success in most crane species'.
As for the stork syrinx, I thought all storks lack syringeal musculature and hence are all mute. Must check..
Ummm, Darren, you're not aware that an alternative common name for species of the genus Mycteria is "wood ibis"? After all, the genus name Ibis was applied to wood storks before ibises.
What about Troglodytes troglodytes? Gram for gram this must be one of the loudest birds. I've always wondered about the source of its vocal power.
Hi Chris. I did know that; I've just checked Fitch (1999) again and it seems pretty clear in that paper that the species concerned is indeed the ciconiid Mycteria ibis. Hmm. I'm going to change the text (again).
The stork Sture that survived the winter is flying about our agricultural districts of both sides of lake Mjoesa, possibly in search of a mate and food. I can confirm that this kind of stork is absolutely not mute. Yesterday I and my visiting sister both heard and saw it. At intervals it trumpeted or whooped very loudly flying low over some fields. Hearing that sound was a first for me, and now I can recognize it from other longnecked birds that live here, cranes, egrets and swans which emit very different sounds. It was fantastic to learn a new bird sound.
Darren, the Swedish trumpeting immigrant was very vocal, it produced a loud and clear outdrawn a-a-a---a. It got to have well a develped syringeal musculature.
About stork vocalizations; Cramp (1986) has information on sounds made by three species of ciconiids: the black stork Ciconia nigra, the white stork C. ciconia, and the (vagrant) African marabou Leptoptilos crumeniferus.
The black stork (p. 327):
"In contrast to White Stork C. ciconia, has well-developed vocal calls. . . Most commonly heard call at nest rather soft 'chee lee, chee lee'. . . Threat-call. . .resembles a prolonged piping, hissing 'fiich'. . . Series of weak, melodius [sic] disyllabic whistles given during head-tossing phase of Up-down display. . . Also utters high, thin, 'hhiio . . . hhiio', sometimes slightly resembling voice of Common Buzzard Buteo buteo. . . Nestlings beg continually. . ."
The white stork (p. 334):
"Calls of Young. More vocal than adults, as soon as hatched uttering distinctive Food-call resembling prolonged mewing of cat..."
Marabou (p. 336):
"Generally silent...but has croaking alarm note."
Reference:
Cramp, S. (ed.) 1986. Handbook of the Birds of Europe, the Middle East and North Africa, Volume I. Ostrich to Ducks, (reprinted edition; original edition 1977), Oxford Unversity Press.
But the the Eurasian crane Grus grus, one of the most vocal cranes, quite often nests very openly. This is quite typical nesting terrain for this species.
Yeah, ok, perhaps I shouldn't have even mentioned the nesting habitat thing: it is certainly not integral to the 'acoustic exaggeration of size' (Fitch 1999) hypothesis. And now I'm very confused about storks.
Thanks for posting another great article!
Great post! I had no idea.
Here it would be all too easy to go off on a tangent and talk about air-sacs and avian respiration, and I regret I can't do that...
Oh, I hope you can talk about it later, the whole issue of avian respiration really confuses me.
the trachea loops upwards near the cloaca, and then extends on the side of the animal's right thigh before looping back to the underside!
So, in theory you could strangle them by squeezing their ass? LOL that's just too funny.
This is why I like reading here. All this time I thought "syrinx" was just a temple in a Rush song.
So, my first thought was "and what about similar apparatus in the non-avian dinosaurs?", and second was "but we won't know unless we have the good luck to find a Scipionyx-type specimen that shows this."
Then I got to your mention of sternums, so it's apparent that we could have osteological evidence on this from dinos.
Anything known?
(And... pterosaurs?)
Well, I've partially answered my own question. Audobon himself observed in the Carolina Wren (Thryothorus ludovicianus) that "The trachea is 1 1/2 inches long, considerably flattened, scarcely 1 twelfth broad at its widest part, and contracting to 1/2 twelfth; the rings 58, with 2 additional dimidiate rings. The muscles as in all the singing birds, those of the inferior larynx considerably developed. Bronchial half rings about 15." Although of a different genus, and not quite as loud as Troglodytes troglodytes, I take this as a hint that tracheal elongation is probably not a feature of the latter.
That, of course, would be John James Audubon.
Wow, this is cool and bizarre stuff. It strikes me that Manucodia must be very vulnerable to predators - a rear attack from the right side, and what would be a flesh wound to most birds would be instant death by severed trachea...
It's interesting that, apart from those incredibly bizarre birds of paradise, the majority of birds with super-elongate tracheae (thanks for that plural, i always thought it was "tracheas") have very long necks already. You'd expect them more in large birds with relatively short necks (big galliforms etc). What's the total length of a trumpeter swan trachea? It must be approaching that of a giraffe, or at least a camel...
OT: I've started uploading the photos from my recent zoo and museum trips here, if you want them for any "picture of the day" posts: http://atpic.com/6163
(They aren't all up yet, because i'm having trouble uploading more than one at once, so it's a bit of a time-consuming process. Check back over the next few days. Everything i post online is anti-copyright.)
The problem of dead air in the trachea of birds and Sauropod dinosaurs has been much discussed and the presence of air sacs seems to successfully explain how they got around it; does this mean that elasmosaurs with equally elongate tracheae also had air sacs?
LeeB.
Darren, that is amazing. I had thought that swans were amazing enough (I mentioned their intrasternal tracheal loop to my two second-cousins recently, when we watched swan-goose combat here )..
but the Birds of Paradise are ludicrous (going beyond even the woodpecker's tongue in the lengths of their invasive absurdity).
If this was April 1st, it would read as a sure spoof!
The dead-air space problem surely needs answered. How do they avoid suffocation or at least shortness (sic!) of breath? Does resonance/vibration in the tube, or peculiarly turbulent airflow somehow, aid mixing and avoid staleness? What are the relative volumes in life of lungs, air sacs and trachea, and variations in these during respiratory cycle? Experiments, charts, graphs, movies, simulations we need!
I wonder whether the trachea in sternum or amongst flight muscles serves for needed heat-exchange: to warm incoming air and cool active major muscles?
When does the trachea go in there? during embryonic development I guess, but how does that progress exactly? I imagine it looks fascinating.. if one can observe that somehow.
LeeB:
..or gills? (grinning mischievously) ..and if so, located where?
How neat it would be, if plesiosaurs were found to have had colourful huge plumes of gill growing off their backs, like seaslugs do! All the restorations would have to change!
(Their long neck of course would be needed to reach back and drive off fishes that might otherwise come to nibble there. Hey.. that gives me an idea.. maybe the gill-covered back of a plesiosaur mimicked a seaweed forest, into which fish would come seeking shelter/food, only to find a hiding mouth on a questing neck awaiting therein to dart at them! Hmm, how mobile/flexible were plesiosaur necks anyway?)
Thanks Graham King,
now if like sea slugs they could store nematocysts from ingested sea anemonies in their gills ( and perhaps over the rest of their skin) it might explain how they could avoid being attacked and eaten while sitting at the surface with their long vulnerable necks exposed as they tried to exhale all that dead air before they could inhale a new breath.
But seriously given that their eyes face upwards they must have been very vulnerable to attack from below, especially on the neck, while breathing.
LeeB.
Elasmosaurs -
Hm, we all know that one of the main reasons why sauropods weren't aquatic snorklers is because you can't inhale with your lungs under 3, 4, 5, 10(!) meters of water.
However, that ought to help you *exhale* quite effectively -
Suppose that elasmosaurs surfaced *vertically*, exhaling as their heads broke the surface (or before, what the heck), and then levelled off to inhale. Seems possible to me.
You mean, when they swallow something it has to go through all those loops???!!
No; that's the wrong pipe. Trachea ≠ esophagus.
Darren:
To cut Fitch some slack, the Eurasian crane may locally also nest in closed habitats, such as reed beds. But that's more likely a recent adaptation to human-induced habitat change, and not typical in most parts of this species' range.
You're not the only one. Someone needs to address the issue of stork vocalizations. Maybe Dr Vector can dissect a representative sample of ciconiid species for us?
Besides the event of loud stork vocalization that my sister and I witnessed, a friend of mine also saw the bird twice afterwards, and he also described the same loud and clear trumpet calls. No croaking sound added like the cranes (grus grus)use.
Whether the stork is male or female, or even adolescent, is uncertain. It looks adult and it is single, and quite dirty by now...
Very stiff.
The white swans I saw flying a decade or so ago on the Sudbury River in MA made a gasping sound like a breathy hee-haw, more or less in synchrony with the beat of their wings. I wondered what possible purpose this expenditure of energy could serve.
Are you sure this wasn't the noise made by the flight feathers? Most swans make a very distinctive metallic buzzing noise as they fly. You can hear it from a long way off, and in fact I've often heard swans long before seeing them.
But many of these birds don't make loud sounds at all! European spoonbill and mute swan, for example!
So:
- they make overlooked, infrasonic sounds (would be pretty cool to discover it in something so familiar as mute swan!)
- elongated trachea is vestigal organ, descended from noisy ancestors.
- tracheal loops have different function entirely!
I had luck to witness display of Trumpet Manucode, on one very snowy day in Berlin zoo. The male made a whole set of sounds, not very loud at all.
And, to you functional anatomy freaks: how chicks of white stork can produce whining and maiowing sounds? I heard them myself.
About cranes and swans. They are open country birds defending very big territories. Their sounds are mostly warnings of breeding pair that the whole area is occupied.
I was wrong when I said that all swans exhibit tracheal elongation: actually, only four do - C. columbianus, C. bewickii, C. cygnus and C. buccinator. Sorry, my mistake. I knew this, as I have a C. olor sternum and is does not have the same sort of tracheal bulge as that shown above for C. buccinator.
European spoonbills grunts and make 'huh' noises during the breeding season: the noises made by these birds don't have to be incredibly loud (though some are) - the point is that they are louder that what would be predicted for a bird of their size. I can't pretend to know anything about spoonbill vocalisations, so it is true that the other species produce quieter noises?
And, Jerzy - are you sure you heard all the noises that the manucode was able to make? They are supposed to make particularly loud squawks.
Time for that bee and flower talk I think.
I very, very much doubt if spoolbill sounds are louder than predicted for a bird of it's size... and of many others.
About manucode - I remember a stream of very different and some rather strange sounds. I'm not sure if I heard all.
There is all this textbook talk about sexual evolution and costly ornaments which signal fitness. But one can notice that ornaments in animals often signal nothing.
Lots of birds with clear sexual dimorphism are monogamous. My favorite example are hornbills, which sprout extreme casques but are extremely monogamous. The same seems to be true about tracheal loops. They often occur in bird without especially loud sounds, and with no special sound displays in life. On the opposite side, there are polygynous and lekking birds which are monomorphic (great snipe, capuchinbird).
I think that sexual ornaments are a sort of vestige organs. They evolve to signal fitness. Cool, but notice how incredibly varied is habitat in spatial and temporal scale.
There are areas rich in food and poor in food, millenia with good food and bad food. Sometimes food is clumped, allowing males to defend it and call females to mate, but sometimes plants (or whatever food) become more dispersed, allowing species to live but only as monogamous one. So gaudy ornaments are in genes, but often the habitat change just breaks down species' original sexual strategy. So there is a lag of millenia where males have tracheal loops or colorful plumage but the habitat changed no longer to permit signalling.
I guess the same applies to eg. dinosaurs. Sauropods might have tracheal loops evolved for sound displays - but many sauropods would change to different mating habitats. Or teropods like Cryolophosaurus or Carnotaurus could have ornate crests, but many species no longer have any elaborate courtship.
Just my separate thought.
I think you raise a very valid point: that structures and behaviours in extant forms do not necessarily represent adaptation to current conditions, as was traditionally assumed. But this is increasingly realised: it has been suggested, for example, that cryptic plumages in flightless New Zealand birds, and super-fast running speeds in pronghorns, evolved under selection pressure from now extinct predators (giant raptors and American cheetahs respectively). If tracheal looping in any species is indeed 'relictual' (and we'd need more work to show that it is), you might predict that it wouldn't hang around for long, given that those tracheal loops appear costly (in metabolic and perhaps fitness terms).
"structures and behaviours in extant forms do not necessarily represent adaptation to current conditions"
Perhaps that should be the standard interpretation for all flora-fauna extant or extinct influenced by Homo sapiens.
I am developing an inexpensive portable infrasound detector that starts recording data as soon as you plug it into a PC usb port. I am close to the Washington, DC National Zoo. What birds do you suggest I test for infrasound?
It appears that the birds are forming a Helmholtz resonator with their windpipes and lungs.
http://en.wikipedia.org/wiki/Helmholtz_resonance
There are two components to this type or resonator: a narrow tube (windpipe) connected to a larger volume (lungs). Lower frequencies are achieved by narrowing the tube (difficult with windpipe), lengthening the tube (that is what is happening here), or increasing the volume at the end of the tube (lung volumes probably need to remain fixed for other reasons.)
It should be possible to compute the resonant frequency from the bird anatomy and the Helmholtz resonator physics (tube diameter, tube length, and attached volume).
Not so instant, actually. About 30 years ago a Wattled Curassow slowly suffocated to death in my arms after the zoo's veterinarian grabbed her wrong. Necropsy revealed a split in the trachea right where he grabbed her around her breast. I knew about the species' unusual tracheal anatomy and tried to warn him, but he rarely paid any attention to lowly zookeepers.
Very interesting!
I really learn a lot!
I think their violins!
=)
Thank you for sharing!
Are these long tracheae air reservoirs,and are they inversely related to air sac size, and/or related to migration distance? Do they affect respiratory rate? What is the tracheal wall anatomy? Do they empty by extrinsic intrabody compression and/or by tracheal wall muscle contraction? The latter would be essential for the subcutaneous lengths.
Unstriped muscle moves food down the gut,urine along the ureter, ova to the uterus, and the fetus to the exterior. Why not air up the trachea?
Mammals,e.g.man are the giveaway! They have a layer of smooth innervated {symp.and para-symp] muscle at the back of their trachea from the cricoid to the smallest bronchiole,which can close them off as every Asthmatic knows. The main tracheal muscle function is obscure; is it an evolutionary remnant now as the dead space is so small?
Surely the 17 metre necked dinosaur in expiration emptied its lungs by the hepatic piston and its airways by an upwards peristalic compressive sweep. The intrinsic muscle relaxation would then allow the highly elastic airway cartilage to spring them open to suck in fresh air for the expanding lungs below. How else?! Dinosaur tracheal rings might have been V-shaped like our thyroid cartilage as against our U-shaped ones, perhaps aiding pumping efficiency. What do you think of that as a theory?
There is no hepatic piston, except in crocodiles with a mobile pubis. Sauropods had air sacs just like birds, and that makes peristalsis in the trachea unnecessary as far as I know, because the volume of the air sacs is so much greater than that of lungs and trachea together.
Expiration empties lungs and air-sacs of effete air up the trachea. The huge volume of this used air in the dead space of long necked creatures would be reinspired unless swept out as part of expiration. The air sac capacity is irrelevant.
The air sac capacity is highly relevant because of the way birds breathe! To inhale, they expand the air sacs, sucking air through the lungs and into the air sacs. To exhale, they compress the air sacs, blowing air through the lungs (in the same direction as during inhaling, but that's not relevant here) and the trachea. The volume of the air sacs is apparently much greater than that of the lung and the trachea together. Bird lungs are very small; they're so efficient that they don't need to be any bigger.
Bernard,
you are right that if all the air in the air sacs has been through the lung and depleted of oxygen then the air in the trachea will be oxygen deficient.
This will then have to be reinspired on inhalation; but as David points out the volume of the air sacs is so much greater than the trachea that further oxygen rich air will then be inhaled.
So on each inhalation the lungs will only be able to extract oxygen from the air brought in from outside, not the air that was in the trachea.
As the trachea gets longer more air will have to be inhaled before oxygen rich air from outside is inhaled.
So as the trachea gets longer the airsacs may have to get larger to increase the total air inhaled on each breath.
There may be a limit on how big they can get which may put a limit on how long the trachea and neck can get.
Both sauropods and elasmosaurs faced this problem, as do long necked birds.
It would be interesting to speculate on how elasmosaurs handled this problem, but there does not seem to be any evidence of the presence or otherwise of airsacs in that group.
Sending oxygen depleted air from the trachea through the lungs seems inefficient, but the recent paper showing the complexity of air transport in the lungs of alligators suggests an answer (at least in sauropods).
Perhaps the air from the trachea was shunted away from the lungs into an air sac directly, and only the oxygen rich air from outside passed directly through the lungs.
Then only the airsac(s) holding the tracheal air would have to get larger as the neck elongated.
I wonder if there are measurements showing differential size of the different air sacs that correllate with neck length.
LeeB.
Thank you both. David,I think you ask a lot of the air sac capacity in the huge long necked dinosaurs.Their minute air requirements, as others have pointed out, needed a tracheal calibre big enough to provide minimal air resistance with short transit time ability. That means big volume. My suggestion is that intrinsic muscle in the tracheal system was a major contributor to expiration in these long necked creatures. It would also result in clean air reentering the air sacs on inspiration. without an initial load of effete tracheal air.
Although no longer used we, representing the mammals, have such innervated muscle in trachea and bronchi. That is no conjecture. It's a fact!
When birds inhale, air from the lungs goes into some air sacs and air from the trachea goes into different air sacs. When they exhale, the air from the first set of air sacs goes into the trachea, and the air from the second set goes into the lungs. The lungs hardly expand & contract at all, which means they can be (and are) a lot more efficient than mammal lungs. Giraffes have a narrower trachea to reduce the problem of dead space; a dinosaur with a neck that long wouldn't need any such special adaptations, and neither, apparently, do birds that have a long trachea without having a long neck.
The air sacs of birds have a large volume. Birds expand & contract their ribcage much more than we do with ribcage and diaphragm; they breathe much deeper and much less frequently than mammals.
Okay David,
if I have this right on inhalation oxygen depleted air from the lungs passes into an air sac and then on exhalation it passes through the trachea where some is exhaled and some remains in the trachea.
On the next inhalation the air in the trachea will be reinhaled along with oxygenated air from outside and pass into an air sac, then on the next exhalation it will pass into the lungs.
So the oxygen depleted air remaining in the trachea is recycled through the lungs.
For this to work efficiently the air sacs have to be much larger in volume than the trachea.
As the neck gets longer the air sacs have to get larger.
Otherwise proportionally more tracheal air would be recycled through the lungs; in the limiting case where the air in the trachea was equal in volume to the air in the air sacs the tracheal air would be endlessly recycled through the lungs until the bird or dinosaur suffocated.
As the neck gets longer there might be selection for the ability to shunt the tracheal air into sacs away from the lungs and then use it to flush the oxygen depleted air from the lungs out of the trachea.
Alternatively, between breaths, the neck and trachea could expand and contract (similarly to the buccal pump of varanids but for a different reason)to dilute the oxygen depleted air in the trachea with oxygen rich air from outside the animal.
LeeB.