How the platypus uses its bill to find prey

Its eyes, ears, and nostrils are sealed underwater. So how does a platypus find its food?

The opening points us toward the bill. Scientists have long known that it contains sensitive nerve endings, but the conclusion about its role in finding prey is recent. The sealed senses make that conclusion plausible. They don't, by themselves, show what the bill does. We should want positive evidence.

First, we learn that the bill has two kinds of receptors. Mechanoreceptors respond to physical pressure. Think of feeling something touch your hand. Electroreceptors respond to weak electric fields. Keep the two functions separate; the rest of the discussion investigates how they help the animal.

Bohringer's work focuses on touch. Stimulating the tiny pushrods in the bill activates a larger area of the neocortex than input from the limbs, eyes, or ears does. That suggests that the bill is an especially important sensory organ. The comparison concerns the area of the brain involved, not a measurement of how strongly the platypus subjectively feels the touch.

The supporting study gives us a sequence: a fine glass stylus touches the bill, a signal travels through the fifth cranial nerve to the neocortex, and then it reaches the motor cortex. The bill snaps, presumably because of impulses from that last region.

That's a lot of anatomical vocabulary for a fairly clear idea: touch the bill, a signal travels through the nervous system, and the bill responds. We don't need a complete map of the brain to follow it. We do need to keep the order straight.

This could explain what happens when the bill comes into contact with prey. But how does the animal find the prey before touching it?

We haven't yet done much with the electroreceptors. They look like a possible answer to the distance problem, and that is the possibility Scheich investigates in paragraph 2.

First, he observes the behavior. The platypus swims while steadily wagging its bill from side to side. Then it switches to erratic movements over a small area on the bottom, homes in, and seizes an object. Something prompts the transition from broad patrolling to focused searching. Is it an electric signal?

Scheich tests that idea with a small battery. The point of the experiment isn't that batteries are food. The battery supplies the suspected cue—a weak electric field—without supplying actual prey.

It works. The platypus turns toward the battery from 10 centimeters away, sometimes as far as 30 centimeters, switches its behavior, and attacks the battery as if it were food. That gives us evidence of both detection at a distance and a feeding response. We aren't just being told that electric receptors exist; we're seeing how they could guide hunting.

There is still a useful question: does the animal's real food produce the same sort of signal?

The shrimp finding answers that. Tail flicks from freshwater shrimp produce weak electric fields and prompt the same response. Now the artificial cue has a connection to a common natural prey. Scheich's group goes on to assume that all the invertebrates the platypus eats produce electric fields, but that broader claim is presented as an assumption, not as a separate experiment on every species.

The two studies fit together. Bohringer helps explain the importance of touch; Scheich helps explain detection before contact. The central discovery is what the bill does during underwater feeding, supported by research into both of its sensory functions.