There have questions before about which foods are most efficiently processed (that is, produces the least amount of waste), but which has the most efficient digestive system?
Good question. I haven’t heard anything to that regard yet, though I know birds have the most efficient respiratory system and the Kangaroo Rat has the most efficient kidney.
WAG: first thing that came to my mind is the humming bird. I have no stats or figures but judging from what the eat(nectar), and how they need so much energy to stay “humming”…i’ll say they are pretty much more efficient in utilizing their diet then other animals…
If by “efficient” you mean “least waste” (and I’m not sure you do), Hydras digest food intracellularly instead of extracellularly like we do, which I think results in complete digestion.
For a college physiology class, a friend and I measured the digestive efficiency of a boa constrictor. We determined how much feces corresponded with a single feeding (one mouse) and measured how many calories was in the feces. By comparing this with the amount of calories in an average-sized mouse, we determined that the boa’s digestion was so efficient, it extracted enough calories from a single meal to support it for nearly a year. The snake’s stomach expands after swallowing it’s prey whole, and it floods with HCl. It can digest bones and cartilage; only hair and occasionaly teeth remain undigested. Most likely snakes are the most efficient digesters among the vertebrates.
Wouldn’t you have to burn the feces to determine its calorie content? :eek:
Yes, Speaker. We dried both the feces and a dead mouse in a drying oven for 24h, then we burned them in a bomb calorimeter. For the record, a mouse has about as many calories as a McDonald’s hamburger patty.
I never knew that. Fascinating. A Big Mac is… how big? And a mouse… I’d think a Big Mac’d contain more calories, being the fatty, greasy bag of empty calories and death fat it is. But no, a dried mouse is more likely to destroy my New Year’s resolution than two all-beef patties. Weird.
By the way, love your username.
Actually, Lodrain, the mouse’s caloric equivalent is just the patty. A Big Mac contains two patties, plus the bun, cheese, and the mysterious Secret Sauce which must contribute untold calories to the product. So dried mice are a viable dietary alternative to Big Macs, and all that fur is likely to contribute to a sense of fullness (much like fiber.)
Okay, I’m convinced.
What’s the best way to cook a mouse?
Isn’t a Hydra a mythological serpant that grows two heads for every one you cut off? 
Yep. But a hydra is also a small carnivorous freshwater coelenterate (an invertebrate from the Greek “hollow gut”). Basically, they’re just small elogated polyps with tentacles and mouths. I’m guessing the name comes from their habit of asexual budding, but I dunno.
I think it is named after the mythical multi-headed creature.
The first thing I think of is a constricting snake (boas, pythons, corn snakes). They digest everything from the hair to the enamel on the teeth. Unlike owls, who urp up the hair, bones, and other indigestibles, snake poo is just a dark brown mass with a smattering of white (urine). Considering such a meal will sate their hunger for a number of weeks, I consider that quite efficient.
Bees convert necter and pollen into honey, which is merely digested food–a.k.a bee vomit.
http://www.straightdope.com/classics/a5_040.html
But bees get a lot of flying out of that stuff.
So, they’re probably good candidates for the title.
Also, the remarks pertaining to honeybees near the bottom of the article here:
http://www.straightdope.com/mailbag/mwarmblood.html
bespeak of a remarkable metabolism.
Thanks for the input so far.
I recall seeing a nature documentary about owls. The owl would catch and eat a mouse and, after a few daays, cough up a ball of undigestible matter - hair, bone, etc. Would this put them in line with the above mentioned snakes?
Owls are efficient, but it seems snakes have them beat. Owls generally don’t digest bones or teeth, as anyone who pulled apart an owl pellet in high school can tell. But they leave behind little else, so they are near the top.
In believe the question is going to be impossible to answer. Efficiency is normally defined as 1/net input - net output. As such it’s going to depend on diet as much as the animal. AFAIK all animals are 100% efficient at digesting pure glucose. If you feed a hydra 100% glucose solution it will digest it at 100% efficiency. If you feed a the toed sloth 100% glucose solution it will digest it at 100% efficiency. Ditto for people, snakes and hairy nosed wombats. That’s the technical answer to the OP as stated: all animals are 100 efficient.
People seem to be answering the question as it relates to the animal’s ‘normal’ diet by talking about snakes, hummingbirds and so on. The question then becomes ‘what animals has the most efficient digestive system at processing its normal food?’. That question is going to be very hard to answer because ‘normal’ varies so much. Animals that live on easily digestible substances like sugars or highly digestible proteins would rate very highly, so the hummingbirds, moths etc would al be in the running, along with chupacabras. Snakes, because they leave so much food behind as hair and bone wouldn’t be as efficient as mammalian carnivores that are a bit more selective about avoiding indigestible bits.
Digestive efficiency doesn’t however normally depend on efficiency at digesting food, since that is so close to meaningless. Instead it normally translates to the proportion of material converted to body weight. Generally speaking the ‘cold blooded’ animals are the best at this, since so little energy is wasted maintaining unnecessary body temperature.
Are there not parasites that lack a developed digestive system; absorbing only the required nutrients directly from the host?
Yeah, most parasitic flatworms, but you’re pushing the definition of digestion if there is no digestive system, and no chemical or physical breakdown.