This supposed to a blog primarily about fly fishing fly but, as you may have noticed, I tend to get side tracked from time to time. And now, in a discussion of animal turds, it looks like this might be happening again. But funnily enough, the two subjects are connected and the link between them is not as tenuous as you might imagine.

Scientists who are interested in studying mammals spend a lot of their time looking at their droppings. It stands to reason. Many mammals are small, secretive and nocturnal, and it is difficult to observe their behaviour directly. But their droppings, if we can find them, speak volumes about what they have been getting up to.

I once took a small group of students to the National Park at Doňana which is one of the last refuges of the critically endangered Iberian Lynx, one of the rarest cats in the world. During a night walk our guides stumbled across an animal dropping which they thought might have come from a lynx. You should have seen how excited they were! It was as though they had stumbled across a winning lottery ticket. The Doňana guides carefully bagged the dropping for further analysis. The lynx turd could yield fragments of bone and fur which might give some insight as to the behaviour of a cat, which is very rarely seen.

The droppings of grazers may not tell us so much but they do testify to the efficiency of digestive systems which are quite specialised. They need to be because grass is quite low in energy and is very difficult to digest. The important task of breaking down the cell walls of the plant cells is done by microorganisms, like bacteria, because no mammals make the enzyme cellulase that carries out this nifty trick. As a result of this, grazers often have specialised compartments in their alimentary canals to house these microorganisms. Most famous is the cow´s “four stomachs” only one of which corresponds to the “true” stomach. The biggest compartment, the rumen, is a huge fermenting tank from which material is periodically regurgitated to be chewed again. This is what cows are getting up to when they are chewing the cud. This way of getting the most out of diet of grass is shared by other familiar ruminants like sheep and goats and deer.

Rabbits are about the smallest mammals that can survive on an exclusive diet of grass. They are obviously too small to house a bunch of stomachs and so they have solved the problems of digesting by the simple expedient of passing the food through the entire digestive system not once, but twice. After the food has gone through the digestive system the first time it is ingested again, in the form of a soft pellet, and passes through the digestive system for a second time. Rabbits, like cows, depend on microorganisms to break down the plant cell walls, but they house them in a long blind-ending compartment called the caecum.

We have a pony grazing outside the house at the moment. The builder, Juan, asked if it could graze on our bit of land and we were happy to have it. I have no idea how long the pony that we have christened “Tony” is going to be with us but, while it is here, it is happily converting the wild growing plants into nice compact manure. Tony, like horses and donkeys, is a hind gut digester and houses billions of bacteria in the caecum and large intestine.

Tony the pony.

Tony the pony.

 

 

 

 

 

 

 

 

 

Tony the pony´s legacy

Tony the pony´s legacy

Pippa with her rabbit, Molly. Maybe bunnies are not as cute as we thought!

Pippa with her rabbit, Molly. Maybe bunnies are not as cute as we thought!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right, enough about turds! What has any of this go to do with fly fishing?

Turds, and particularly cow turds, can be good or bad for fishing. A fresh cow pat is larder for a variety of insects and other invertebrates like dung flies. A fresh cow pat, with the consistency of porridge, may not look too appetising to us but for little bugs it´s like getting a Christmas hamper! For the fly fisherman this can be good news too. We can tie up an imitation of a dung fly and see if there is a trout nearby who wants to play ball.

A Dung Fly

 

 

But cow shit is, on the whole, bad news. If it seeps into streams and makes its way into rivers or lakes it artificially enriches the water and acts, as it does on land, as a fertiliser. This can lead to through the proliferation of algae to a process called eutrophication. It is this process which has had very damaging effects on places like Lough Sheelin although I believe it was the wastes from pigs rather than cows that were to blame.

I was prompted to write about this because of a very interesting letter published in this month´s Fly Fishing and Fly Tying Monthly and sent in by David Pilkington. It would seem that pour on insecticide chemicals which are given to farm and domestic animals can affect the droppings also which can become toxic to invertebrates. Not only are the insects which would normally breakdown wastes affected but, as a natural consequence, so too are the birds which feed on them. And the cow pats, no longer broken down by the usual hordes of invertebrates, remain wet and slimy and more likely, perhaps, to find their way into a water course where it causes a whole bunch of problems.

It is a worrying problem and a reminder, if we need one, of how we can pay a price which is often indirect and far from obvious, for intervening in the natural order of things even though we might have the best intentions.