Subject: Re: Echolocation in Diving Birds
Date: Feb 9 17:57:34 1997
From: bboek at olympus.net - bboek at olympus.net


Sorry this got sent as an incomplete message before. Here is the whole
thought:

Michael, you raise an excellent question about diving seabird feeding
techniques to which no one probably has an answer.

I suspect that, firstly, deep-diving seabirds have exceptional eyesight
that enables them to see in remarkably low light levels. Nocturnal
alcids like Cassin's Auklets (not really a deep diver) are able to
navigate quite well on extremely dark, moonless nights, finding their
burrows with ease when humans are groping around unable to see more than
their hand in front of their face. Even surface-feeding nocturnal
seabirds such as storm-petrels are able to fly incredibly zig-zaggy
flights on very dark nights, suggesting they, too, see in very low light
levels. Do these birds have extremely high density of light recepters in
their eyes to pick up images in low light?

Since all these seabirds are quite vocal, they may not need to click
bills to echo-locate as you suggest. Could they also just vocalize
underwater? Sounds like an experiment to be done with captive birds,
like at the Seattle Aquarium.

My guess is that they are so "in tune" to their underwater world, that
they use every sense they have to locate prey items, like predators do
everywhere. But your questions are excellent ones. It make one wonder
how an Emperor Penguin can find and capture fast-swimming squid when more
than 100 meters deep, well below the photic zone, especially during the
Antarctic winter. An experience we can never really "fathom!"