Tetrapod Zoology

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I’ve just been writing about waterfowl for the day job. Which is fine, because waterfowl are among my favourite animals (as if that isn’t obvious from Tet Zoo… what, you mean it isn’t obvious?). Entirely because they’re on my mind at the moment, here is the first of several, entirely random waterfowl facts…

Geese are consummate herbivores, and should be regarded as the avian equivalents of grazing artiodactyls and perissodactyls…

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Except that they can fly. And they’re much smaller. And they can’t digest cellulose (by which I mean: they lack a gut flora that breaks down cellulose). Rather than cropping vegetation with a specialised dentition, geese crop plants with a robust bill where the lamellae (typically soft and flexible) have become heavily keratinised tooth-like serrations [shown here, in a Tundra bean goose Anser serrirostris; picture by D. Naish]. In some species, the serrations are obvious in lateral view and form an area of the bill termed the ‘grinning patch’. Unlike artiodactyls, geese don’t utilise a multi-chambered stomach and caecum; instead, they simply rely on rapid transit of large quantities of fodder, quickly expelling unwanted fibre and maximising energy intake by selecting the most digestible parts of favoured plants. Geese of some species can spend as much as 41-46% of any given 24 hrs eating: in some species (like Barnacle geese Branta leucopsis [shown below; from wikipedia]) this increases to 62% when other, competing species (like Pinkfeet A. brachyrhynchus) are present (Madsen & Mortensen 2008). Some goose species have been reported to spend as much as 17 hrs out of every 24 eating (70% of the day) when they need to rapidly put weight on during winter, and White-fronted geese A. albifrons [one shown at very top; from wikipedia] will spend 90% of their active day foraging when food is scarce. Geese feed rapidly, pecking at rates of between 80 and 200 times per minute (Owen 1980). For comparison, bovids seem to eat for about 33-40% of any 24 hrs, and horses are reported to spend c. 50-66% of a 24 hour period eating.

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Goose digestive efficiency is very low compared to that of many other vertebrate herbivores: as mentioned above, they can’t digest cellulose, and some species only absorb c. 25% of the nutriment available from the plants they eat. In fact, goose droppings still contain so much recoverable nutriment that some mammalian herbivores can meet all of their dietary needs by eating nothing but goose shit (van der Wal & Loonen 1998). White-fronted geese and Barnacle geese produce a dropping every 3.5 minutes during their active period, meaning that 140 dropping are produced over 8 hours of feeding. Each dropping weighs 0.7-1 g when dry (note: DRY). Because the geese also produce droppings on the roost after feeding in the evening, they are estimated to produce 150 droppings a day at least.

150 individual droppings seems like a lot, but I was interested in seeing how it compares to bodyweight. And 150 g of droppings for an animal weighing 1.7-2.4 kg or so isn’t particularly high: it’s 11-16% of bodyweight per day. Horses produce 15-23 kg of dung per day, and given average-ish weights of 380-550 kg, this amounts to c. 4% of bodyweight per day. Cows produce about 55 kg of dung per day, amounting to about 11% of bodyweight (assuming a cow of 500 kg) [however: see comments. I forgot that I'm comparing DRY WEIGHT of goose droppings vs WET WEIGHT of mammal droppings].

I must note that the amount of time that geese spend foraging, the amount of nutriment that geese absorb from their food, and the nutritive content of their droppings all varies hugely depending on where they are in their moult cycle (Fox & Kahlert 1999) [feeding Barnacle geese in Finland shown below; from wikipedia].

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More amazing waterfowl facts tomorrow! For previous Tet Zoo entries on waterfowl see…

Refs – -

Fox, A. D. & Kahlert, J. 1999. Adjustments to nitrogen metabolism during wing moult in Greylag geese, Anser anser. Functional Ecology 13, 661-669.

Madsen, J. & Mortensen, C. E. 2008. Habitat exploitation and interspecific competition of moulting geese in East Greenland. Ibis 129, 25-44.

Owen, M. 1980. Wild Geese of the World. B T Batsford Ltd, London.

van der Wal, R., & Loonen, M. (1998). Goose droppings as food for reindeer Canadian Journal of Zoology, 76 (6), 1117-1122 DOI: 10.1139/cjz-76-6-1117

Comments

  1. #1 iayork
    June 18, 2010

    Are the cattle and horse dung figures you give also dry mass? I’m guessing that the cattle figure at least is not dry (implied in e.g. http://www.dairyingfortomorrow.com/uploads/documents/file/effluent%20management%20database/chapters/characteristics%20of%20effluent%20and%20manure.pdf), and by dry weight the goose figure would be more exceptional.

    I can’t believe I just spent 10 minutes looking up cow poop on the internet. What a wonderful future we live in.

  2. #2 Darren Naish
    June 18, 2010

    I really would welcome a more rigorous look at dung masses as compared to body masses: the figures I provide were hastily pruned from the internet and I’m not surprised to see that I’ve partially screwed up (for one, by comparing dry weight for the geese vs wet weight for cows and horses). Further thoughts, data and calculations appreciated!

  3. #3 Jerry D. Harris
    June 18, 2010

    OK, so geese can’t digest cellulose…but I thought no tetrapod could — it was all done by various gut bacteria. So here you mean that geese lack the gut flora necessary to break down cellulose, yes? If so, then what is it about their gut chemistry that is inhospitable to those bacteria? Or it is just the lack of food residence time brought on by the smaller size of the geese vs., say, perissodactyls, and that having a complex, ruminant-style digestive apparatus would probably make flight more difficult and energetically expensive…?

  4. #4 shiva
    June 18, 2010

    Will you be covering hybridisation in waterfowl? I have a number of photos of probable hybrid anatids, including one *very* odd-looking small goose that is unlike anything i’ve seen (even in “hybrid bird” photo pools on Flickr).

    http://pic.atpic.com/1727205/600

    I’m fairly sure one of its parents is Anser sp. and the other is Branta sp. (and probably not A. anser, A. cygnoides or B. canadensis because of the size, which is about that of B. bernicla or B. leucopsis), but that’s about as far as i can get… any ideas?

  5. #5 Jerzy
    June 18, 2010

    Try http://www.birdforum.net, they are good for ID.

  6. #6 Alan
    June 18, 2010

    Presumably it is their need to fly which prevents geese developing a heavy, cellulose retaining gut. This makes me wonder about the Australian Dromornis – did they feed like geese or like ratites?

  7. #7 John Harshman
    June 18, 2010

    You forgot to mention the common simile for speed and ease, “Like shit through a goose” (prominently featured, if I remember, in the movie Patton), though you do supply the reasons. I do hope you’ll be covering the polyphyly of “geese”.

    There is of course one gut fermenter that flies, the ever-annoying hoatzin. There are so many weird things about hoatzins that the one species would be worth quite a few posts. I’ll even supply a title for one about their digestive systems: “Alimentary, hoatzin”.

  8. #8 Cale
    June 18, 2010

    I know this is kinda obvious, but do y’all think that goose feeding styles could almost be compared to (extremely miniaturized) sauropods?

  9. #9 Jim Thomerson
    June 18, 2010

    The only time I have really observed and contemplated goose poop was in Kew Gardens. I was impressed with how abundant and green it was. Your cow and horse figures sound high to me. Hoatzins are neat birds. They are said to smell bad, but I never noticed. Is it a matter of Hoatzin burps, I wonder.

  10. #10 Sebastian Marquez
    June 18, 2010

    I’ll even supply a title for one about their digestive systems: “Alimentary, hoatzin”.

    That is epic. I wish I was more familiar with my Doyle to engage in a witty repartee.

  11. #11 David Stern
    June 18, 2010

    I was a post-doc at University of York which seemed to be an ideal goose habitat. There was an artificial lake in the middle of the campus and lawns all around. That’s when I first learned about the vast amount of droppings that geese could produce :)

  12. #12 John Scanlon, FCD
    June 18, 2010

    I spend part of nearly every workday contemplating dromornithid bones and trying to explain, to a wide variety of museum visitors, what these giant birds would have been like in life. Most of my background understanding comes from Murray and Vickers-Rich, but also Oliver Wings’ PhD and Jaqueline Nguyen’s Honours thesis (see refs below). In describing their appearance, locomotion and feeding, I frequently make comparisons with extant birds that folks are likely to be more familiar with: ducks, geese, swans, magpie goose, emu, cassowary, ostrich, moa, dodo… and hoatzin. It’s pretty well known now that droms were anseriforms, and they had relatively large heads and powerful jaws so they were presumably using their beaks to process food in a goose-like manner rather than the weak-jawed ratites’ pluck-and-swallow. They have about the stubbiest, most hoof-like toes of any birds; one species seems to have been reasonaly cursorial, but mostly they have similar broad pelves and limb-bone proprtions to anseriforms, and presumably would have waddled like freaking big ducks.

    Apart from the bones, very common fossil remains of these birds are piles of pebbles. Lacking the cow’s or hoatzin’s bacterial fermenter, other herbivorous birds need to mash their food between rocks to break open those indigestible cell walls; because the gizzard works like a rock tumbler, it’ll end up with only the hardest available rocks grinding each other into smooth ellipsoidal shapes. For example, a Baru feeding-site on a river bank, preserved in late Oligocene limestone, has bones of at least four ‘Big Bird’ (unnamed species cf. Bullockornis/Dromornis), one Barawertornis, two Emuarius, and one Eoanseranas, and has also produced at least 30 kg of chert pebbles, mostly ground pretty smooth, but not transported by water (based on absence of rolling wear and sorting of bones in the deposit). If Oliver Wings’ ostrich ratio (~1% gastroliths by weight) can be applied as a rule of thumb, those few square metres of sediment record the death of about 3 tonnes of herbivorous birds (slightly, not hugely more than we can account for by identifiable skeletal elements).

    How much poop per day from that bird community, I will leave as an exercise for the reader.

    Nguyen, J.M.T., W.E. Boles, and S.J. Hand. 2010. New material of Barawertornis tedfordi, a dromornithid bird from the Oligo-Miocene of Australia, and its phylogenetic implications. Records of the Australian Museum 62: 45–60. doi:10.3853/j.0067-1975.62.2010.1539

    Wings, O. 2004. Identification, distribution, and function of gastroliths in dinosaurs and extant birds with emphasis on ostriches (Struthio camelus). Ph.D. Thesis, The University of Bonn, Bonn, Germany, 187 pp.

    Worthy, T.H. and J.D. Scanlon. 2009. A new genus and species of Magpie goose (Anseranatidae) of Oligo-Miocene age from Riversleigh, northwestern Queensland, Australia. Journal of Vertebrate Paleontology 29: 205-211.

  13. #13 Jenny Islander
    June 19, 2010

    This leads to some ideas for that alternate Azores landmass I mentioned in a reply to your May 2 post about giant tortoises. Do these sound plausible to you?

    *Boar-goose. (Actually it’s descended from a duck, but these are translations of hypothetical names given by the Norse discoverers of Azoria, who weren’t much for comparative anatomy.) About 1m tall, bill shoe-shaped and hooked, wings long arms with vicious bony clubs, feet adapted for scratching the dirt. Omnivore, will mob small or weak animals (which are literally nibbled to death by ducks).
    *Brawler. Two species of very large (half-ton?) and ponderous bird, related to the boar-goose, but herbivorous. The smaller species travels in flocks as protection from the local giant raptor birds and predatory rodents, while the larger is too big to worry. Both carry their chicks on their backs. Even the smaller species can easily club a grown man to death.
    *Swan-horse. Several species of tall, long-legged anatid, one of which is dazzling white with buff accents. Fastest land animals in Azoria; the chicks can run shortly after hatching. While they have a nasty kick, they depend mostly on speed for survival. All species move in flocks.

    I had these dreamed up some time ago. I decided that the brawlers and swan-horses were grazers, browsing niches having been occupied by tortoises long before Azorian anatids became flightless. However, I hadn’t considered the poo issue. Might there be a niche for, say, the dung-eater, a gracile (for a tortoise!) animal that follows the migrating flocks and lives almost exclusively on their feces? Surely there would also be drastic effects on local plant life as well, particularly grass growth and seed transportation.

  14. #14 Sven DiMilo
    June 19, 2010

    I’ll even supply a title for one about their digestive systems: “Alimentary, hoatzin”.

    Best biology pun ever, but not original. It was the headline to an article in Discover (iirc) many years ago.
    Hoatzins are kind of crappy fliers and they definitely prefer not to, by my observations. They do have a cellulose-digesting microflora, housed in the foregut. Very cool. But they’re folivores, and I wonder how well they’d do on grass alone.
    Here in the NE USA, everybody that lives near a body of fresh water of any size larger than a puddle knows all about Canada Goose shit. Many local populations seem to have decided that migration’s not worth the effort any more and their year-round, uh, productivity is a real problem.

  15. #15 Willem van der Merwe
    June 20, 2010

    Yeah the hoatzin pun is good, but there was also another good one here a while ago – with a prehistoric scene painted by Darren if I remember right – the comment ‘Yes, archosaurs rule, but you need lepidosaurs for scale’.

    Now where else on the ‘web can you make jokes like that?

  16. #16 Dartian
    June 21, 2010

    shiva:

    any ideas?

    How about either 1) Branta leucopsis X Anser albifrons, or 2) Branta leucopsis X Anser erythropus?

  17. #17 shiva
    June 23, 2010

    Dartian – i think you may be right, having looked at pictures of Lesser White-front (a species i’m not too familiar with in the wild), the odd shape of my hybrid’s forehead and bill are definitely reminiscent, and its coloration does look like what you might logically expect to get from crossing that with Barnacle (the only thing that doesn’t quite fit being the uniformly dark breast/belly – i’d perhaps have expected more of a distinction between the areas which are black and almost white on B. leucopsis – however, there’s too much white on the face for the Branta parent to really be anything else). Both of the White-fronts also have the pink bill/orange legs combo…

    The only reason i hadn’t really considered that combination was that all the pictures i had previously found of Barnacle x White-front crosses had been more Canada-brown in the body rather than my bird’s almost bluish grey – but there was some debate over whether the Branta parent in those cases was actually Barnacle or Cackling/a small race of Canada, and Joern Lehmus (who appears to be the go-to person for anatid hybrids) said that combination was “variable”. I think i’m going to go with “probable” B. leucopsis x. A. erythropus.

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