A quick review of interesting research on living things from the last month.
Birds learn to avoid unpleasant tastes from others
The bright colours of toxic insects save their bird predators from getting a taste of them. If every bird had to learn from experience, poisonous insects might not have much of an advantage. In fact, their colourful bodies would stand out, and they’d be picked off as soon as they showed themselves. To be effective, they’d have to warn the birds of their distasteful nature before they are injured or killed. How do birds learn to associate colour with foul taste?
Great tits discover by watching others. Researchers filmed one deal with an almond covered in a bitter liquid and played the recording to others. When these television-watching birds encountered a similar item, they knew to avoid it. But other great tits that didn’t have the benefit of the tutorial had to discover the unpleasant taste for themselves.
Unusual mirrors help scallops see
Beads of blue eyes stud the two lips of the scallop’s semi-circular mantle. Some species have as many as 200 eyes. Instead of using a lens to focus an image on the retina, these marine bivalves angle concave mirrors. Light passes through two retinas, one below the other, before it hits a grid of layered reflective material. Made of square guanine crystals, these mollusc mirrors reflect the image up to the retinas. Should the likeness of dark shadowy shapes strike the upper retina, the scallop panics and escapes. The lower retina offers peripheral vision in dim light. The rods and cones of our single retinas function similarly as the scallop’s dual ones. The visual processing centre, the parietovisceral ganglion, receives all the images from the many eyes to produce one perspective.