View From The Shed by Volunteer Shaun - IT'S POO-POO TIME!

IT’S POO-POO TIME!

This week’s blog is dedicated to inquisitive children of all ages. It covers a series of questions that we’ve all probably asked ourselves at some time or other (and if not, why not?) and it’s a recognised stage of childhood development which some of us never fully grow out of. I’ve never been one to shy away from the baser aspects of life so let’s get on with it.

I’m talking, of course, about our fascination with digestion and its inevitable by-products. Be aware, there will be talk of solids, liquids and gases. You have been warned. 

I’ve got several Big Brilliant Books of Bird Biology (I’m a sucker for anything alliterative) and I’ve been delving deep into them for my - and your - education and entertainment. They clearly show that a bird's digestive throughput system works in a way that’s very different to ours. Put simply, you and I eat and drink. These yummy provisions go into our tummies where all the fuel and goodness is taken out and the waste product passes on and leaves the body. Liquids come out of our front (depending on your personal plumbing arrangement) and the more solid unwanted material comes out of the back. I hope I’m not being too gross here but I need to lay down some very basic basics before showing how birds’ anatomy differs from mammals’ in this particular department. It’s about to get a little grim but I guarantee that it’s going to be interesting. Brace yourself.

Like us, our feathered friends’ dietary intake often dictates the content and consistency of their excreta. If you’ve ever parked beneath the roost of a bird who regularly dines on dark berries then you’ll know exactly what I’m talking about. But how come ‘bird lime’ (as my Granny used to call it) is always so (and there’s no other word for it)...  sloppy?

Birds do not have a bladder or any way of disposing of liquids in the way that mammals do. Their internal (and external) piping system is very different to ours. They have kidneys to filter the nasties from their liquid intake, just the same as we do, but their kidneys are much less efficient than a human’s. So much so that they have to reabsorb much of the waste liquid back into their bodies for another round of filtering until eventually the concentrated urine is excreted as the white sloppy part of their faeces. 

Stop laughing at the back, this is serious stuff. Just as different birds have developed differing tastes in the foods that they eat, they have also found different ways of dealing with what comes out of the other end, especially at a young age. No bird wants their offspring’s droppings messing up the nest. It’s unsightly and unhygienic. A sullied nest would quickly attract ticks, mites and other unpleasantries so some degree of toilet training is required. This takes one of two forms.

The chicks of small birds (such as Tits, Finches and Sparrows) that have no way of defending themselves from nest predators usually produce their poo sealed within a white membrane packet called a faecal sac. The parent bird then takes this gift-wrapped bag of delights away from the nest. This is partly to keep the nest clean and also so that it doesn’t leave a tell-tale stench that might attract a predator. Some adult birds will deposit this deposit some distance away from home (again, throwing any hunter off the scent) but others will actually eat it. The sac is a great, if gross, source of proteins, fats and nutrients. If the youngster cannot process them yet then the parent may as well have the benefit. Nothing goes to waste in nature but I can only think that it’s a good thing that birds’ sense of taste is so underdeveloped.

Larger, meat-eating birds differ somewhat. They don’t produce this faecal sack. They don’t really have the same problem of being targeted by a ground-based predator as they’re well equipped with sharp and point weaponry from a very early age. They do however still have the same cleanliness requirements but they dispense with their waste in a very different way. The big parts of their food that they can’t digest - bones, fur etc - gets coughed up in the form of a pellet. Note that only meat-eating birds do this and they won’t be able to eat again until they’ve honked up a pellet from their previous meal. Delightful.

All birds have the same large and small intestine combination as us to remove the good stuff from their food and pass out the undigestibles but the addition of the liquid concentrated urine element (from a few paragraphs ago - keep up) makes it extra squirty. This is especially useful for predator chicks who are yet to fledge as they can act like particularly disgusting water pistols and jettison their waste over the edge of their nest, thereby avoiding befouling their home. Mum would be so proud.

Regardless of what kind of food goes in, eventually the waste comes out of an opening at the rear end of the bird called a cloaca or vent. Both males and females have this same cloaca which they also use for mating (before you ask, Mr and Mrs bird just press them together in a ‘cloacal kiss’) and egg laying. But there’s no expulsion of gas from this orifice. I know you’re wondering about it so I’ll get straight to the point. They don’t create a build up of gas within their digestive system so no, birds don’t fart. Don’t say that these blogs aren’t educational.

So next time a pigeon flies over and decides to drop a little gift on your shoulder, don’t just rant impotently at it. Take a moment to marvel at the natural wonder that has happened in its innards before it anointed you. And maybe you might want to buy a lottery ticket too. You know what they say about ‘luck’...