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…
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.
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].
More amazing waterfowl facts tomorrow! For previous Tet Zoo entries on waterfowl see…
- Duck sex: to interfere, or to watch?
- Pink-headed duck and Red-crested pochard: who would win in a fight?
- The Madagascar pochard returns (again)
- Lo, for I have seen the Meller’s duck, and it was good
- Duck humps dog, and other stories from the world of waterfowl sex
- Ridiculous super-elongate, coiled windpipes allow some birds to function like trombones – - or is it violins?
- Harbour seal kills and eats duck
- STOP ‘feeding’ the ducks
- Attack of the flying steamer ducks
- Meteoroid vs goose… again
- 2007: a good year for terror birds and mega-ducks
- Tet Zoo picture of the day # 10 (on Swan goose)
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