Hi all,
I have a curiosity question. In the sporting world, baseball for example, players are known to paint a black strip on their cheekbone. It is meant to stop the glare of the sun reflecting off the cheek and interrupting their view of the ball, target, whatever. As I look through my photos and the field guides I am noticing a reverse strategy. Lots of bird species have either a row of white dots or a white line on or near the bottom eyelid. As it appears on many birds across many families I don’t imagine that it is just a cosmetic predilection for white eyeliner.
Birds I have noticed it on include Aus Spotted Crake, White-browed Scrubwren, Black Noddy, Common Noddy, Southern Emu-wren, Shy Heathwren, Male Magpie-lark (but not the female) etc etc. Does anyone know if there is a reason for these small white lines near the bottom eyelid on some but not all dark-headed species? Oh, and I don’t include birds with large white patches on the cheek or around or near the eye, just the ones with a small, discrete, white mark or row of white dots on or near the bottom eyelid.
cheers
Jenny http://jenniferspryausbirding.blogspot.com.au/ ===============================
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Hi Jenny,
Sure nature is full of curious questions and trying really hard can give some answers, some of which are supportable. Of course there are also surely many more birds that have dark or black markings around the eyes, supposedly for the same reason as you mention (“In the sporting world”). I can’t think of any reason for what you ask other than social signalling. It is sort of like someone asking a few years ago why does a White-faced Heron have a white face, to which I asked why does a White-faced Heron have grey body. It is after all like an egret, most of which are white. I don’t know which came first.
It would appear that birds (and most other animals) devote a lot of energy and genetic input into producing colours and colour arrangements, when logic suggests just being all white would be simpler. Clearly the disadvantage of being all white (presumably from attracting predators and not being pretty enough to attract partners or having more difficulty signalling what species you are) outweighs this. My only hint would be that small patches of white on the face and maybe near the eye are ways of achieving benefit of reducing the amount of colour needing to be produced in bits of the bird small enough and intimate enough to not be a disadvantage in terms of attracting predators. Yet still achieve social connections with partners at close range maybe by highlighting the eye to partners, which may well be an effective cosmetic predilection for white eyeliner (seems like a good benefit to me).
So is my suggestion correct? I have no idea and wouldn’t know how to prove it anyway.
Philip