Why are Sea Birds Greyscale?

[sedesdraconis]

Somebody was wondering to me recently (I don't remember exactly who, chances are sarkat), "why are sea birds almost always black and white?" I didn't have anything to say at the time, but I was thinking about it yesterday and today

Comments

[jadeilyn]

Blue footed boobies are not grayscale in the most fabulous way possible.

[sedesdraconis]

It's true. A number of seabirds have bright colors on their legs and beaks, blue footed boobies not least among them.

Which just makes the problem even weirder. Why would seabirds have almost universally greyscale plumage, but regularly sport colored beaks and legs; a pattern vanishingly rare on land?

I've got a couple of guesses, but they're pretty weak as hypotheses go.

[jadeilyn]

How noticeable are their feet from the air? Maybe it satisfies whatever reason they need to be drab while on the move while still looking handsome to the booby ladies. (I know the females have blue feet too, but still.)

[sarkat]

I have no recollection of asking about this. Or wondering about it. Or even NOTICING that sea birds tended to be more black and white. So it probably wasn't me.

[shalyndra]

huh. That was really cool to read and think about.

[chironsoldier]

watch life of birds, it's an awesome series.

then again, sometimes it's interesting to think up reasons for things using only previous knowledge on a subject and forming hypotheses based on similar instances, etc.

so, if you want david attenborough to tell you everything (or at least a lot of interesting things) about birds, watch life of birds. if you want to keep thinking on your own, go for it.

my hypothesis is the camouflage one and it has to do with where seabirds are being comouflaged (grey sky against clouds? through how many feet of water? on a rocky cliffside, or sandy beach, or?? are they in a large flock?)

as for feet, they can be colorful but i don't think it has to do with sexual dimorphism because at least in blue footed boobies i think both males and females have blue feet. i know some egrets (snowy or cattle, i forget) use their toes as bait to lure food, but i don't know if that applies to seabirds since they are wetland birds more than anything.

[sedesdraconis]

I've seen life of birds, I doubt he answers this question to my satisfaction (but it has been a while, I should re-watch anyway).

The camouflage hypothesis doesn't stand up to scrutiny, as far as I'm concerned. The pattern of which species have light and dark on top vs. bottom, and what colors the chicks are, and all the things you'd look at to see if camouflage was important, just don't add up. The correlation isn't strong enough to explain the strength of the dichotomy.

i don't think it has to do with sexual dimorphism because at least in blue footed boobies i think both males and females have blue feet.

Well, males and females do have consistently different blue feet, but yeah, there's still extraordinarily low dimorphism compared to land birds, as there is in effectively all sea birds. The blue feet definitely are used in sexual display, even so.