Remember that a male stickleback will

and court this:

"The ubiquitous Pheasant Tail"

We can apply an ethological approach to explore the possibility that several flies made from pheasant tail fibres incorporate sign stimuli that elicit feeding behaviour in trout.

Frank Sawyer introduced the Pheasant Tail nymph - a simple fly construced from copper wire and dark pheasant tail fibres to imitate Baetis nymphs - which is cast upstream of the trout so it sinks to trout's level. Then the rod tip is lifted so that the fly ascends in the water in front of the fish- the 'induced take'technique.

Sawyer (1979) commented:
"General shape and colouration,together with the right sizeis of greater importance than an exact copy. My two universal patterns, as I call them, are the Pheasant Tail and the Grey Goose. The Pheasant Tail serves for the darker coloured nymphs and the Gray Goose for the lighter ones."

The effectivenees of simple flies constructed from pheasant tail fibres is not restricted to English chalkstreams. Arthur Cove's Pheasant Tailwas developed to imitate 'buzzers' (chironomid midges) on Eyebrook reservoir. The American Al Troth based his Pheasant Tail nymphon Sawyer's original pattern but used peacock herl as thorax material. The Teeny Nymphis another example of a simple but effective trout fly which may imitate a shrimp. Size and colour variations of Jim Teeny's basic pattern have been responsible for catching 25 IGFA (International Game Fish Association) fresh and saltwater world records.

The simplicity of these flies suggests several candidates for sign stimuli that elicit a trout's feeding response:

• movement - these patterns tend to be fished with some form of movement
• colour - colour is often varied to match the colour of the natural nymph
• thorax - is present but construction materials vary (Sawyer and Teeny used pheasant tail; Cove used rabbit fur and Troth used peacock herl)
• body shape - designed to represent shape of natural (Sawyer and Troth tied a straight body to reprent a mayfly nymph; Cove tied around the hook bend to represent chironomid pupae)
• the ratiobetween body size and thorax may be important when representing particular insect groups

• body made of pheasant tail fibres
• thorax made of pheasant tail fibres
• movement imparted by the angler

Application of Lloyd Morgan's Canonwould suggest that an artificial fly constructed with a straight body from pheasant tail fibres and some form of thorax which is moved in the water should catch trout. It is interesting that the flies constructed by Sawyer, Cove, Troth and Teeny are more elaborate than this simple pattern. For example, Sawyer's nymph has a tail. However this analysis does not consider the possibility that the tail is a sign stimulus when trout are feeding selectively on mayfly nymphs. Likewise, the curved body in Cove's fly may be a sign stimulus when trout are feeding selectively on chironomid pupae. Thus selective feeding may be the result of the operation of a "search pattern"consisting of several sign stimuli.

Thus several different sign stimuli may act together to trigger the trout's feeding behaviour. Trout may 'add-up' sign stimuli to determine if an object is edible. This would be an example of the law of heterogeneous summationwhich predicts that incorporating several sign stimuli into an artificial fly could increase its attractiveness to trout. In fact, the law suggests that these artificial flies could be more attractive to trout than the natural insects they are supposed to represent.

If an ethologist was asked to investigate which of these features (body, thorax, movement) elicit the feeding response, they would construct even simpler flies which incorporated just one element

No ethologisthas attempted this task

However the writings of experienced anglerssuggest that the 'sign stimuli' involved may be:

1. the outline of a nymph represented by a thorax composed of a few wire wraps
2. movement of the 'model' in the water - the 'induced-take' technique

• Raymond Baringfound that a Pheasant Tail nymph increased in attractiveness as it became more and more bedraggled and finally lost all of its original dressing

• Ed Zern(1979) described how he caught trout on a pheasant tail nymph that was " a bare size 18 hook with three turns of fine copper wire around its short shank and nothing else - no fur, no feather, no silk, no tinsel."

• Oliver Kitealso reported success with his ' bare hook nymph'which consisted of a few turns of wire wrapped around the hook shank. He was also able to catch trout whilst blindfolded by using the 'induced-take'technique

• Inspired by Kite's success, Roy Christiedeveloped his Copper Wire Hare's Mask fly with which he has "..spent many hundreds of hours using this system and caught thousands of trout with it." But he adds:" Does it always work? Well, no."

The question remains "Why not?" Is the answer because the trout are 'educated'?We need to bear in mind Lloyd Morgan's Canonwhen searching for an answer.

In his book 'Trout Flies' Dave Hughesremarked "Many folk think that if fish aren't taking their nymphs, they need to change flies. Most often all they need to do is change depth. Fish a foot or two deeper, and suddenly the same fly is remarkably effective." The Brassie(shown on the left) is an example of a simple fly that will sink quickly.

Final thought

Despite all the above, I continue to accumulate yet more fly-tying materials and expensive tools and avidly consume information on new and old fly-tying fads and fancies. I still tie over-elaborate flies. I use a Snowbee Waldron vice which is almost a work of art even though I know that master fly tyers such as Rim Chung use a simple pair of forceps to hold the hook. I suspect all this complexity gives me a sense of confidence. The rational side of my brain whispers that it matters not one jot to the trout!

References and online resources:

• Sawyer "Nymphing in the Classic Style" in Migel Wright (Eds) "The Masters on the Nymph", 1979, published by Ernest Benn, London.
• Zern "Bye-Bye, Wet Fly?" in Migel Wright (Eds) "The Masters on the Nymph", 1979, published by Ernest Benn, London.
• Roy Christie's article on the Copper Wire Hare's Ear
• Skues, "The way of a trout with a fly" published by A and C Back, 4th edition, 1949, p 91
• Sawyers nymphs
• Bob Ireton articleon tying and fishing the Teeny nymph
• Jim Teeny's flies. Look under 'Fishing Tips' for Jim's video showing how to tie his Teeny nymph
• An appreciation of Jim Teeny and his nymphby Peter Cockwill originally published in "Flydresser" contains clear and detailed tying instructions
• The IGFA (International Game Fish Association) website
• Loren Williams's clearly illustrated article on tying Al Troth's American Pheasant Tail nymph
• Martin Cottis' article on tying Cove's Pheasant Tail Nymph
• In a 'spoof' article (B J Britton, J Grimley Evans and J M Potter,"Does the fly matter? The CRACKPOT study in evidence based trout fishing", British Medical Journal, 1998)the authors compared the GRHE against other dry flies on a well stocked chalkstream. The authors are cordially invited to replicate their findings on a population of wild brown trout!
• Rim Chung's website with tying instructions for his RS2 nymph and using forceps as a vice
• Snowbee-Waldron fly tying vice
• A collection of flies tied by Al Troth including his pheasant tail nymph
• John Simonson's blog entry about the visual capabilities of fish: Fly Patterns For Trout
• Description of Parallel Mechanisms for Visual Search in Zebrafish

Further information on parallel visual search
1. Parallel Mechanisms for Visual Search in Zebrafish
2. Visual search article in Scholarpedia
3. Inhibition of return article in Scholarpedia
4. Underwater camera flyfishing 1080p- 2014 best fishing video winner
5. Trout on a dry fly from an underwater camera
6. John Simonson blog entry: What triggers a trout to eat your fly?
7. How Does a Trout Catch a Fly?: Marinaro's "Edge of the Window Theory"
8. Discussion of selective feeding in Nymph Fishing Rivers and Streams: A Biologist's View of Taking Trout Below ... By Rick Hafele