When otter droppings make enjoyable reading

Where the hill stream runs out into the strand, one tuft of grass on the bank grows a lush and distinctive green, as if regularly sprinkled with fertiliser. I pause there often, checking for a small, black dropping a couple of centimetres long. Sometimes I pick one up and give a deep sniff at it, like a connoisseur of cigars. "A pleasant, sweet, musky, fishy odour which is quite unmistakable," as James Fairley says. "Once inhaled, it is never forgotten." It was 25 years ago that the professor, through An Irish Beast Book, first encouraged me to sniff an otter's spraint, a momentous rite of passage for any would-be naturalist. I am delighted, in his new book, to find half a dozen pages devoted to spraint, its content and significance - even to meticulous drawings of three separate specimens spiked with fishbones.

The otter's regular sprainting places are called seats. "With practice," says Fairley, "one almost begins to think like an otter, and at times one can predict seats with a degree of accuracy that is almost uncanny. Collecting spraints is also satisfying: a walk along a river bank on a fine day to gather them is to me unquestionably the most agreeable sort of routine fieldwork."

In the 1970s, the professor was one of the very few mammalogists at work in Ireland, and his Beast Book proved a popular triumph. Its successor is a similar inimitable mix of impeccable science, vivid anecdote and the fascinating practical minutiae of mammal research.

Its title, A Basket of Weasels, is some of Fairley's Belfast mischief, since Ireland has no - definitely no - weasels, and the book proceeds from chapters on the island's mustelid family (stoat, mink, badger, otter, pine marten) to others on bats, rabbits and hares, even rats and mice, all of which - and more - have enriched his lifetime of research.

Its prime purpose, apart from sheer enthusiasm for natural history, is to bring out the wealth of new Irish research that has been building over the past few decades, much of it lying unpublished in student theses and official files. In his decades at University College Galway (he retired in 1999 and went back to Belfast), Fairley himself inspired a whole raft of badly-needed work on Irish mammals, not least in persuading young women students that bats might be fun after all.

"So as not to harass the bats, Shiel and her brother never radio-tagged more than one in an evening. They caught the animal in a hand-net as it emerged and sexed and weighed it. She then placed it on her brother's knee, with a piece of cloth over its head to quieten it, and trimmed the hair between its shoulder blades with scissors. The radio tag was attached with Skinbond, a surgical glue. The animal was kept in a cloth bag until the glue had dried and then released . . ."

Such detail is compelling, and the rich potentials of radio-tagging tempt the professor to digress briefly on the physics of sound waves. But his own research has more often meant serial analysis of stomach contents, faecal droppings or regurgitated owl pellets to answer questions on wildlife diets and distribution.

With a cautionary note on the "indisputably nasty" smell of mink scats, he gives hints and tips on identifying food fragments with all the zest of a forensic pathologist.

An otter spraint, for example, is best left overnight in hot water with a pinch of Steradent denture-cleaner. When sieved next morning, "everything identifiable is then squeaky-clean and bright". In the past 20 years, zoologists have analysed almost 10,000 spraints in Ireland, sometimes to compare the prey of otters and mink, sometimes to see where trout and salmon fit into the otter's diet.

Large fragments of fish, frogs and birds are often quite easy to classify, but the insect bits and pieces in a bat's dropping can need more experience. A page of examples (the wing of an earwig, the antenna of a midge, a scarab beetle's jaw, the beautiful scales from moth wings) encourages the student to be patient with the mysteries under the microscope.

It is the uninhibited assumption that the field and laboratory craft of research sits perfectly well into a popular book about furry animals with a lovely painting on the cover that gives A Basket of Weasels its special character. So long as natural history is served, Fairley sets no barrier between the professional scientist and the eager amateur observer.

Indeed, he sought the help of Irish Times readers in plotting the extent of the feral mink's spread, and at times he borrows from anecdotes in Eye on Nature - a badger surprised while murdering a hedgehog, for example, or stoats that go fishing in pools beside the sea.

He has long been fascinated by stoat behaviour, and his Beast Book chronicled some graphic encounters with stoat-packs travelling around in autumn. Here he suggests a gruesome explanation for the acrobatics - leaping about and turning somersaults and cartwheels - so often interpreted as play in the young animals, or, in the adults, as a way of bemusing a rabbit or bird intended as prey.

Dr Fairley, however, also observed this in a solitary stoat: "The exhibition, which lasted several minutes, was at times too fast for the eye to follow, and included flying somersaults reminiscent of those by human gymnasts, but at lightning speed." Like all mammals, the stoat carries parasites, of which the nastiest is the horrifying skull worm, the almost unpronounceable Skrjabingylus nasicola. Dissection of a fresh road casualty can find a mass of these roundworms packed into the animal's sinuses. It may be, says Dr Fairley, that the stoat's gyrations are fits resulting from pressure on the brain, or attempts to relieve unbearable irritation.

James Fairley's Beast Book was given two editions by Blackstaff Press, but A Basket of Weasels (with exquisite drawings by Roy Gaston), is published privately, in a print run of 1,000. It can be bought direct from Dr Fairley (15 Luxor Gardens, Belfast BT5 5NB) at £21 (or £17 sterling), or through bookshops.