DavidHowdon's picture

Is this defensive colouration?

Observed: 28th January 2013 By: DavidHowdon
Amateur Entomologists' SocietyLondon Natural History SocietySelborne Society
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0366 Bearded Reedling_D_15a
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Female 0366 Panurus biarmicus (Linnaeus) (Bearded Tit) - Hyde Park, Middlesex (VC 21), 28th January 2013
Description:

I suspect there are several pictures of these very obliging London visitors on iSpot. Added these ones here on the basis of a discussion I had with other birders at the 'twitch' about the appearance of the birds from the rear. The impression given is (to my mind quite strongly) is that of the a head of a much larger bird (the wings forming 'eyes' and the tail the bill).
I speculated that this could be defensive, giving the impression of a much larger bird (about goose sized) which might deter a predator like a Sparrowhawk from trying to take them.
The brief research I have done so far does not suggest that this is the case (it's not mentioned). Does anyone know?

Identifications
Species interactions

No interactions present.

Species with which Bearded Tit (Panurus biarmicus) interacts

Comments

Ray Turner's picture

Interesting Idea

I don’t have a clue David but it is an interesting hypothesis. I must admit to being fooled momentarily when your observation first opened up and the brain hadn’t quite computed what I was seeing (looking at photo one). Indeed my instant reaction was exactly as you describe, a bird with some sort of weird elongated beak and dark eye stripe.

I think to be more than a hypothesis though the bird would need to display some use of this ‘evolved’ trait, such as turning its back towards a threat.

Ray

Ray

DavidHowdon's picture

Hypothesis

I'd deliberately selected and cropped the first image (its the same photo as the 6th image) to show the effect well, and put it first so it would be the image on the various iSpot displays to put people in the position you were when seeing it.

Not sure my idea is so advanced a thought as to merit the name hypothesis. Using the markings in an 'evolved trait' way would be useful evidence. But quite a lot of things (particularly insects) use such markings in a more passive way to avoid predation, so it may be that simply having the feature would provide some defensive behaviour.

Anyway beardies are rare enough round here (and hard enough to observe) that I doubt I will ever be able to do anything to test this hypothesis.

JonathanWallace's picture

It's an interesting idea but

It's an interesting idea but the fact that it requires the bird to face away from a predator seems likely to increase the risk of being predated by at least as much as the putative resemblance to a larger bird might reduce it. It seems to be an idea that could perhaps be tested experimentally though.

Jonathan Wallace

JonathanWallace's picture

sorry - accidentally posted

sorry - accidentally posted the same comment twice. Deleting the second

Jonathan Wallace

Aláine's picture

This is very interesting

This is very interesting indeed. If this is the case this theory applies to more species than the bearded tit. Many tit and bunting species share simular plumage patterns. Perhaps your theory could apply to them also and this could make experimentation much easier. To observe a bird turning it's back on a predator would definately be a signifigant find.

I must add if the intention of such an adaptation would be to 'confuse' or 'deter' a raptor, I'm not sure how effective that would prove considering all birds of prey see eight times better that we do and have over 40 times more light receiving cells on the inner retina that humans, allowing them to see even in ultra violet. It would be remarkably difficult to so easily fool a raptor, I would imagine.

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www.alaineartandphotography.blogspot.ie

notpop's picture

possible

saw a male sparrowhawk cross my gate and take a sparrow from the hedge in approx .25 of a second at the weekend.
I doubt if even a highly tuned hawk could see this was not part of a large bird in that time.
Even if this saves the prey species in only isolated instances,that is enough for evolution to favour the pattern.
For example the 'eyes' of a Peacock butterfly will often fail to fool a predator,but so long as they fool some predators the pattern becomes selected evolution.

Aláine's picture

A valid point notpop. I do

A valid point notpop. I do agree if it were to work on some predators the trait would be adapted.

I've been staring at bird's rumps, that's bad comming from a 15 year old girl! I've looked at finches, tits, warblers, bunting, wagtail, dippers, waders and waxwing. This theory would deffinately apply to a waxwing, many of the others are questionable but potential such as goldfinch, chaffinch, long tailed tit and wagtails.

If your suggesting that birds with markings such as that of the bearded tit are attempting to mimic larger birds with longer bills many of these would be shore birds, large ducks, geese, swan species etc. Why doesn't the theory apply to smaller shore birds open to predatation such as the reed warbler, dipper or wagtail (although it could be debated as to whether or not it applies to the grey wagtail.) If it does apply to the grey wagtail could the wagtail's bobbing be potentially mimicing the head movement of a larger bird?

The theory dosen't seem to apply to any small wader.

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www.alaineartandphotography.blogspot.ie

Ray Turner's picture

Different Lifestyles

You make a good point Aláine but to use notpop’s example from above not all butterflies exhibit an ‘eye’ on their wings as does the Peacock. Different species evolve in different directions as the evolutionary pressure on them is different, determined by their niche in the ecosystem.

Ray

notpop's picture

fish

I suspect the most numerous examples of eyes at the tail end occur in marine fish species.
Many butterflies have eyed tails e.g. Long Tailed Blue.
These seem mainly intended to make predators grab the wrong end.
This may result in a bite out of the tail,often seen in butterflies,but may make the difference between escape or death for the prey.
So your bearded tit example may even be inviting attack !