why dippers dip...theory (1 Viewer)

[tonyjames]

I saw on tv that no one knew for sure why dippers bob up and down and there was a thread on here a while ago but then it came to me while looking out the kitchen window with the blinds down..
Im convinced they dip so they can see through the interference pattern on the suface of the water, especially apparrent in small pools near flowing water. Te effect is very much the same as looking at an object behind a fence, it comes into focus when moving at a certain speed like film at the cinema. They dip at just the right speed for this to come into effect enabling them to identify insects through the waters surface..

 

[matthompson]

Sounds like a great theory. I'm sure its probably to do with something key like feeding as they do it when they are on there own too. I've just been filming them in North wales, great bird and when they unfold there wings you can see how well they are designed for underwater manoeuvres.

Now if you can just prove that theory ;-) !

 

[Vectis Birder]

When I saw the thread title, I thought that someone had come up with a theory as to why we miss birds and how to see more. :-O

 

[Farnboro John]

Dippers dip because:

1. They leave birds too long (e.g. waiting till the weekend, rendering them vulnerable to Friday Night Flit, which is practically a social disease).

2. They spend time trying to get a full car instead of going on breaking news (this results in being five minutes or even five seconds too late which would be a hell of a way to miss Pacific Swift I'm sure.)

3. Half the time they decide its too far to go for that species - but if an honest attempt to see the bird has not been made, is that a dip?

4. They have a life beyond birding e.g shopping, washing, cleaning, football, family......

5. Increasingly, they haven't the nerve to go overnight but wait for morning news, which results in them missing every bird that roosts but naffs off the moment it wakes up. Last winter's Cornish Gyr could not have been seen by anyone following this, the Unsound Approach to twitching.

Do for a start? I bet someone has more!

John

 

[Jos Stratford]

Answer is obvious, they wouldn't be dippers if they didn't dip

 

[pianoman]

Heard somewhere that it was for the same reason wagtails wag - ie to disguise their outline against fast-flowing water. Don't know how well this stands up, though it does seem to make them harder to see because you don't get a recognizable silhouette against the moving background.

 

[Lawts]

Dippers dip because:

1. They leave birds too long (e.g. waiting till the weekend, rendering them vulnerable to Friday Night Flit, which is practically a social disease).

2. They spend time trying to get a full car instead of going on breaking news (this results in being five minutes or even five seconds too late which would be a hell of a way to miss Pacific Swift I'm sure.)

3. Half the time they decide its too far to go for that species - but if an honest attempt to see the bird has not been made, is that a dip?

4. They have a life beyond birding e.g shopping, washing, cleaning, football, family......

5. Increasingly, they haven't the nerve to go overnight but wait for morning news, which results in them missing every bird that roosts but naffs off the moment it wakes up. Last winter's Cornish Gyr could not have been seen by anyone following this, the Unsound Approach to twitching.

Do for a start? I bet someone has more!

John

Interesting question re when does a dip constitue a dip? My theory is you need to be at the site where you could have technically seen the bird had it been there. So, for example, if I drive half way to a bird, get stuck in traffic and have to turn round and go home, that wouldn't be a dip.

Another I'd add as a reason, is leaving it too long so the number of birders on site reduce the chances of the bird being found - to see this form of dip taking place join me at Walney on Saturday. Come to think of it if enough of you do it might then not be a dip! Hurrah!

Also the weather, I can recall dipping some birds because of constant bad weather on the day you go, with the bird reappearing again in better weather the following day - the Flamborough Desert Warbler did this to me, but I got the little chap eventually a few days later.

 

[KnockerNorton]

I'm not sure it's due to feeding, as they tend to dip when they're not feeding too. I think it's part of the same question as why wagtails wag and dunnocks wing flick and doves raise their tails on landing - although I'm not convinced by the predator theory either! (or else why would yellow and pied 'wag' too? And what about Dunnock). It must be some kind of signal, and it must be important otherwise it would have died out as it must take up a fair bit of energy. Perhaps it's to do with advertisement to conspecifics? To make them visible rather than invisible? To advertise fitness somehow? It's notable that the thing which is 'dipped' on dippers is the white throat patch, and the thing which is wagged in wagtails is the unecessarily long tail, the thing which is lifted in doves is the boldly patterned tail...as for dunnocks, hmmm!.

 

[Docmartin]

Why do Dippers dip? Because they don't know the words.

Oh no, sorry, that's the wrong joke.

 

[paulstamp]

Refraction?

I guess Tony you watched the same program I did as I've just been discussing this with colleagues at work.

My theory is similar - that its very difficult to judge distance through water from a single standpoint because of the refraction of light passing through it, so getting two alternative viewpoints would provided a much better picture of where potential prey is.

Other birds that watch and hunt prey from under the surface of the water tend to come from higher up - and the distortion from refraction is reduced the closer to vertical you are... kingfishers, herons and egrets all would have less of a problem with refraction than a dipper that sits inches from the surface of the water.

 

[Steven Astley]

I guess Tony you watched the same program I did as I've just been discussing this with colleagues at work.

My theory is similar - that its very difficult to judge distance through water from a single standpoint because of the refraction of light passing through it, so getting two alternative viewpoints would provided a much better picture of where potential prey is.

Other birds that watch and hunt prey from under the surface of the water tend to come from higher up - and the distortion from refraction is less the closer to vertical you are... kingfishers, herons and egrets all would have less of a problem with refraction than a dipper that sits inches from the surface of the water.

I reckon that's a good theory. And the reason egrets and herons don't dip is because they are looking form above so distortion is not as bad.

 

[paulstamp]

I reckon that's a good theory. And the reason egrets and herons don't dip is because they are looking form above so distortion is not as bad.

Cheers Steven - I made a hasty edit to my post originally as I realised that coming from a higher angle would reduce the problem of refraction.

 

[Farnboro John]

Interesting question re when does a dip constitue a dip? My theory is you need to be at the site where you could have technically seen the bird had it been there. So, for example, if I drive half way to a bird, get stuck in traffic and have to turn round and go home, that wouldn't be a dip.

Another I'd add as a reason, is leaving it too long so the number of birders on site reduce the chances of the bird being found - to see this form of dip taking place join me at Walney on Saturday. Come to think of it if enough of you do it might then not be a dip! Hurrah!

Also the weather, I can recall dipping some birds because of constant bad weather on the day you go, with the bird reappearing again in better weather the following day - the Flamborough Desert Warbler did this to me, but I got the little chap eventually a few days later.

Thought of another one over the weekend - how many people missed the Glaucous-winged Gull through leaving the site too early? (Or allowing themselves to be distracted by the Pacific Diver!) Grim though it can be, staying till dusk is the only option if you really want to see the bird.

A variation is stopping on the way to the bird, I've heard lunches quoted in dip stories before - no meal's that good!

John

 

[KnockerNorton]

I guess Tony you watched the same program I did as I've just been discussing this with colleagues at work.

My theory is similar - that its very difficult to judge distance through water from a single standpoint because of the refraction of light passing through it, so getting two alternative viewpoints would provided a much better picture of where potential prey is.

Other birds that watch and hunt prey from under the surface of the water tend to come from higher up - and the distortion from refraction is reduced the closer to vertical you are... kingfishers, herons and egrets all would have less of a problem with refraction than a dipper that sits inches from the surface of the water.

But that theory seems to me to be fundamentally undermined by the fact that dippers are not 'ambush attack' predators, like heron and kingfisher. They walk along the bottom and disturb critters by probing about among pebbles and searching under rocks and in weed etc. They don't seem to identify prey from the surface and then attack it - they find it and grab it as they go along, already submerged, using the specialised nictating membane to improve underwater perception.

 

[paulstamp]

But that theory seems to me to be fundamentally undermined by the fact that dippers are not 'ambush attack' predators, like heron and kingfisher. They walk along the bottom and disturb critters by probing about among pebbles and searching under rocks and in weed etc. They don't seem to identify prey from the surface and then attack it - they find it and grab it as they go along, already submerged, using the specialised nictating membane to improve underwater perception.

I take your point that this behaviour would only be appropriate if they ambush prey, but is it true that they only forage and never ambush?

I've seen reports of them plucking nymphs from rocks just below the surface as well as "fly catching".

 

[Jos Stratford]

Given that they are frequently in mountain streams and I'm sure that water is darn cold, maybe they are just in a perpetual state of extreme shiver, hence the bobbing up and down!

More seriously, I'd agree with Poecile here, they are underwater foragers first and foremost, if not exclusively, so an adaption to ambush attack would seem unlikely.

 

[KnockerNorton]

I take your point that this behaviour would only be appropriate if they ambush prey, but is it true that they only forage and never ambush?

I've seen reports of them plucking nymphs from rocks just below the surface as well as "fly catching".

yeah, but plucking nymphs is a bit different from a splash and grab. And fly-catching speaks for itself - not much need for head-bobbing to counter refraction!

Again, the striking white blazon seems to be the focus of the dip. It's the bib that gets bobbed. Or why else have a gleaming white chest like that? Gotta be a low-level display of some kind, surely?

 

[Rich Facey]

Randler, Animal Behaviour, volume 71, pages 1089-1093. Basically the guy tested three leading theories of why wagtails wag/dip/bob - signal submission, flush prey, or vigilance. Basically concluded that it was the latter as it was done during none food orientated activities such as preening and resting etc as well as when the birds were foraging. I suppose its a bit like spronking in antelopes.

 

[Steven Astley]

Don't know about wagtails but with Dippers I have noticed they start dipping when they notice me just before they fly off, so that ties in with what Rich says.
Actually I think Jos idea isn't that funny as they use air to keep themselfs warm in dips, maybe its way of getting air into there plumage.
Had good opportunities watching dippers this year with a nest on my patch. Could be imagining this but don't they greet each other with more pronounced dips.

 

[paulstamp]

yeah, but plucking nymphs is a bit different from a splash and grab. And fly-catching speaks for itself - not much need for head-bobbing to counter refraction!

Again, the striking white blazon seems to be the focus of the dip. It's the bib that gets bobbed. Or why else have a gleaming white chest like that? Gotta be a low-level display of some kind, surely?

I'm not convinced its anything to do with the white bib - after all the American Dipper still dips but has no bib!

The point I'm making about fly catching is that the dipper has two or three methods of feeding not just foraging, although the dipping behaviour is so prominent you'd expect it to be applicable to its main method which I concede is foraging.