Tag Archives: biology

Very hungry caterpillars

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It’s almost a pity that we introduce children to caterpillars so young. The magic of the transformation of a squishy, unimpressive tube into a living, fluttering creature apparently made of stained glass gets muddled up with the rest of the magic of childhood and is too easy to forget when we grow up. Everyone knows about caterpillars turning into butterflies, but almost no one really thinks about it.

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Photo by Andrea Westmoreland, reproduced through a Creative Common license from Flickr.

Even before they turning into butterflies (or moths), caterpillars are impressive. They hatch tiny, into a bird-eat-caterpillar world, and their one crucial job is to grow big in time to metamorphose. This isn’t a particularly complex task—there’s a reason caterpillars are basically just digestive systems on legs—but it isn’t necessarily easy, either. They need to find the right food and eat it quickly without being eaten themselves.

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The pros and cons of trying to eat everything

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The noble California Gull, a diet generalist

Animals eat different things. Every kid knows about herbivores vs. carnivores. Strangely, the other type of diet variation—diet breadth—is much less generally known. Generalists have broad diets, being able to eat a wide variety of things, while specialists eat only a few types of items. Anteaters and hummingbirds are specialists; the seagull who flew off with your lunch is a generalist.

Being a generalist gives a species a lot of advantages, especially in unpredictable environments. The more you can eat, the less likely you are to run out of food. An anteater without ants will starve, but a seagull without fish can eat crabs, or carrion, or Cheetos.

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Or whatever this is.

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Double rain

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Before I studied juncos in California, I studied House Wrens in New York. Most days in the spring and summer I biked from my basement apartment to my field site, which had the no-nonsense label Unit One. The bike ride was an adventure in itself: I prepped for the field season by relearning how to stay on a bike, which I hadn’t done since childhood. (Contrary to the popular saying, it appears I can forget how to ride a bike.) On my way to Unit One I often came upon large snapping turtles stumping deliberately across the road, on the turtle-slow prowl for places to lay their eggs.

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Unit One was primarily a field site for studying Tree Swallows. The front half of it was short grass broken up by regular rectangular ponds, over which the swallows stooped and swirled. House Wren territory lay past the manicured domain of the swallows, in forest dense with brush and mosquitoes. At the start of the field season I feared getting lost in it: the paths were overgrown, and I have a poor natural sense of direction.

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Is that a friendly (woolly, stingy) face I see?

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Humans see faces everywhere. We see a face in the craters of the moon, in wall sockets, sideways in punctuation :-) and just about anywhere else two dots and a line are arranged in even approximately the same positions as two eyes and a mouth.

Don't those drawings of outlets look like faces?

Don’t those drawings of outlets look like faces?

Once we recognize something as a face, we process it differently from other visual stimuli. Certain parts of the brains are triggered preferentially by faces. We are especially good at perceiving faces: we can pick out matching faces faster than matching abstract patterns, and distinguish non-matching faces more easily than other images. This only works, however, when our brains recognize the faces as faces: if you flip faces upside-down, they no longer trigger the “face” switch for us, and we become much worse at distinguishing them. The same thing happens if you digitally scramble facial features, so that there’s an ear in the middle and an eye on the chin and a mouth slanting across the forehead, or any other mix-up that makes the face no longer be arranged like a face. Our brains are specialized to perceive face-shaped patterns much better than other patterns.

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Do birds have a sense of smell?

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Not too long ago, the generally-accepted answer to this question would have been: “Not really—a few birds do, but most don’t.” This was largely based on the observation that most birds have very small olfactory bulbs in their brain relative to their overall brain size. As we observe bird behavior, however, we are are increasingly realizing that most birds can and do use smell regularly, often for very important things.

Let’s begin with the birds that have been known for a long time to use smell. Kiwi birds are unique in having their nostrils on the end of their bills, rather than close to the base of the bill like all other birds. Kiwis stick that long bill into the soil and use their nostrils to sniff for insects and worms.

Brown Kiwi chick. Photo by Smithsonian's National Zoo*

Brown Kiwi chick.
Photo by Smithsonian’s National Zoo*

It makes a lot of sense that kiwis have a good sense of smell, even if you think that birds in general don’t, because kiwis seem to have evolved to be the avian version of a small fuzzy mammal. Kiwis evolved on the islands of New Zealand, where the only mammals were bats. The small-brown-fuzzy-nocturnal-snuffling-in-the-dirt-for-worms niche was open for the taking, and kiwis—flightless, nocturnal, and covered in long thin feathers that are highly reminiscent of hair—took it. A good sense of smell goes with that niche.

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The beauty and the beast; or, a tale of two moles

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The Beauty

Technically, golden moles are not true moles—they are more closely related to tenrecs than they are to true moles—but golden moles are small, burrowing, insect-eating mammals that, with their streamlined heads and powerful digging claws, have converged to look a lot like true moles.

With at least one key difference: golden moles shine. They shimmer. They iridesce.

Juliana's golden mole. Photo from ARKive.

Juliana’s golden mole. It’s a bit hard to see the iridescence in photographs, but it’s there. Photo from ARKive.

The hairs on a golden mole reflect light in such a way to give the animal a sheen, ranging in color from gold to green to purple. In the museum where I work, we have some preserved specimens of golden moles, and they are remarkable to see: their fur shines and shimmers like the coat of a child’s stuffed toy unicorn.

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Seeing song: an interview with a partially deaf ornithologist who studies bird song

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Alma Schrage is a recent graduate of UC Berkeley and a research assistant in the Bowie lab in the Museum of Vertebrate Zoology. Over several years I have watched her become an ornithologist. In this interview she discusses her research on bird song and how it has been affected—or not—by being partially deaf.

Alma in the field. Photo courtesy of Alma Schrage.

Alma in the field. Photo courtesy of Alma Schrage.

Why study bird song?

It’s interesting on several different levels. If you’re interested in cognition and behavior, bird song provides so many different things to study. You can also study how vocalizations tie in with genetics, morphology and such to help provide a fuller picture of the bird, or you can study the factors that drive development of bird song such as different acoustic environments, and selective forces on calls and songs.

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Does food taste the same to animals as it does to us?

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Every day, I feed my cat small, round, hard pellets that look about as appetizing as old gravel, and she gets so excited about them. I tasted one (for you, dear readers!) and I would describe the taste as falling somewhere between the meh of cardboard and the bleh of rancid fish. Not recommended. For her part, the cat flinches if I consume an orange anywhere near her; you can tell she thinks I am disgusting for eating them. It seems pretty clear that she and I have different tastes in food. Are such differences simply matters of individual preference, or is there a biological basis for them?

As in all things, I am right and you are wrong about this.

As in all things, I am right and you are wrong about this.

It’s hard to know what something tastes like to someone else. My personal experience of peanut butter (disgusting) is likely to differ from yours (mmm, yum), despite our belonging to the same species. However, we can say with some certainty that both of us can taste peanut butter, and that it will not taste like lemons to either of us. Humans have five major types of taste receptors: sweet, umami, bitter, sour, and salty. Sugar is sweet, hamburgers and mushrooms are umami, coffee and India pale ales are bitter, lemons are sour, and salt is salty.

And mice are micey.

And mice are micey.

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Let’s talk about bird tongues

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Ferruginous Hawk. Photo by Nathan Rupert*

Ferruginous Hawk. Photo by Nathan Rupert*

You don’t have to look at many birds to realize that they are very variable in appearance: hawks look different from hummingbirds, and both look different from peacocks. You can spend a lot of time looking at birds, though, before you realize that they are hiding a lot of variation inside their mouths: long tongues, short tongues, spiky tongues, curly tongues, forked tongues, frayed tongues, brush-like tongues.

Like bird bills, bird tongues are specialized to each particular bird’s way of feeding. Birds that feed on nectar have tongues specifically adapted to nectarivory, often with many little protrusions at the tip of the tongue, giving it a frayed or brush-like appearance. This brushiness increases the surface area of the tongue, making it better at picking up nectar.

Rainbow Lorikeet. Photo by Alan (Kaptain Kobold)*

Rainbow Lorikeet using its brush-like tongue to feed on flowers. Photo by Alan (Kaptain Kobold)*

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