You’ve gone to peek at a nest. For a moment, all the little feathered heads regard you with large, dark eyes—and then in a flurry and a tumble they are out of the nest, running every which way along the ground, and their parents are scolding you and swooping among their babies in apparent panic. Oh no! Will the babies be okay?
This is possibly the question I am asked most frequently. Sometimes the inquirer has managed to catch a few of the babies and replace them in the nest, only for the babies to promptly hop back out. Other times the babies have swiftly vanished, and the inquirer—often someone who has watched the nest over the course of weeks, growing attached to their fluffy neighbors—is left, quite suddenly, with silence and absence and a gnawing guilt.
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.
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.
Every park has at least one weird duck. It’s the wrong colors—all white, or patchy white; its bill bright storybook orange or its face weirdly red and lumpy. Next to the other ducks it looks oversized and bulky, like a linebacker in a crowd of quarterbacks.
How new species form, and what determines whether they last, is one of the major topics in evolutionary biology; and much of this topic is embodied by that one weird duck.
When I was kid, I thought I didn’t like cats. It didn’t help that every time I got near one, my eyes got itchy and my nose ran. My cat allergy disappeared around the time I went to college, where I volunteered at the local animal shelter and got a new perspective on felines. In the second year of my PhD program, I went to the East Bay SPCA and adopted a 3-year-old former stray.
I love my cat. She is 40% sweetheart, 40% terror, and 20% judgmental staring statue.
It looks like I’m sleeping, but I am watching your every move.
I am an ecologist, an ornithologist, and a bird-lover, so I know some things about cats that a lot of cat lovers may not. It all adds up to this: humans have put cats into an ecological trap, and we continue to do so, often with the best of intentions. It is not the cats’ fault. It is our human duty to get them out of this trap, for the cats’ sakes and for wildlife.
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.
Or whatever this is.
If you live in a temperate climate and pay attention to your local birds, you have probably noticed that their preferences for companionship change with the seasons. In spring, pairs stick close by each other and three’s a crowd—any third-wheel interloper is likely to be chased off in a flurry of angry wingbeats. But in fall and winter, the birds suddenly become community minded, travelling around in flocks of dozens of their fellows. In Chicago in the winter you can find trees liberally decorated with the round orange forms of fluffed-up American Robins, bearing more than a passing resemblance to Christmas tree ornaments. Even in the Bay Area, not generally known for its seasonal variation, huge flocks of quietly chirruping Dark-eyed Juncos make it clear that (mild, occasionally rainy) winter has arrived.
Not pictured: about fifteen of this robin’s winter friends.
Why flock in winter? Or, why flock only in winter?
I wrote about birds and mirrors a while ago, and not much has changed scientifically since then. Most bird species tested have interpreted their own reflections as other individuals, responding either with aggression or courtship. Female pigeons who view their own reflections ovulate, apparently interpreting their reflections as suitable mates. Among birds, only magpies, so far, have been demonstrated to understand that the mirror reflects their own image, although pigeons can be trained to use spatial information from mirrors correctly in the real world.
So why bring this up again? Recently I saw a Yellow-rumped Warbler interacting with its reflection in a car side mirror, and took a video with my phone. Here it is (apologies for the lack of zoom):
At the time I took the video, I didn’t think much of it beyond general amusement. But rewatching it, I began to have some questions.