Animals interact visually all the time. Males try to look big and scary to rivals, or sexy to females. Prey animals try to look inedible—or better, invisible—to predators. Sometimes these animals use visual trickery to assist their cause.
You’ve probably encountered visual illusions before. Here are some classic ones:
a) The vertical line looks longer than the horizontal line, even though they’re both the same length. b) The top line looks longer than the bottom line, even though both are the same length. c) The middle circles are both the same size, but the one on the left looks bigger. d) The middle grey rectangle is just solid grey, but against the gradient background, it looks like a gradient. e) Both circles are the same shade of orange, but the one surrounded by black looks brighter.
Animals can use visual illusions a) and b) to appear bigger by changing their posture. Vertical stances make you look bigger than horizontal ones, and making a Y with your limbs looks bigger than letting them fall down. So if you’re a male peacock spider trying to look big and sexy to a female, you can raise a pair of back legs up in a Y to look bigger than you really are.
Peacock spider display. Photo by Jurgen Otto*
Sometimes the titles of scientific papers are so surprising that they seem to transform into news headlines in my head:
Adoption of chicks by the Pied Avocet – Adoption of fledglings by Black and Red Kites – Caspian Terns fledge a Ring-billed Gull chick – Adoption of young Common Buzzards by White-tailed Sea Eagles
How can this be true? Raising chicks is hard; it takes energy and time and risk. Why would any bird make those sacrifices for an unrelated chick?
Okay, I would absolutely adopt this guy.
Pied Avocet chick. Photo by Keith Marshall
When you’re an altricial baby bird, life is either great or over. If it isn’t over—that is, assuming you aren’t eaten by a mouse, chipmunk, snake, slug, coyote, etc.—then your life is sitting still in the warm and having food shoved in your face. Excellent.
Reed Warbler chicks. This is the life.
Photo by nottsexminer
But that doesn’t last. After you fledge, your parents keep feeding you, but soon they start feeding you less. You can follow them around begging, but soon even that doesn’t do any good. You have to face it: you need to learn how to catch your own food. But that food flies and crawls and runs away!
Doesn’t matter. I can catch it.
Photo by David Mikulin
We tend to think of wild animals as “instinctually” being able to do everything they do, but in fact, a lot of those skills have to be learned and practiced. Two of my favorite scientific papers looked at how fledgling birds developed their foraging skills. As adults, they were the expert bug-catchers you see all the time; but as fledglings, they did—well, about as well as the four-year-old child of a champion fisherman would do, the first time you handed her the fishing rod.
In many bird species, the males have to acquire and defend a good territory – filled with great food or great places to put a nest – in order to have a prayer of attracting a mate. There’s even evidence that some females pay more attention to the quality of the male’s territory than to the quality of the male, so having a good territory is a big deal.
In these species, males fight a lot. They fight to get territories and then they fight to keep them. It’s a bit like a football game: you have to run fast and smash into people in order to get the ball, and then continue running fast and smashing into people (and withstanding them smashing into you) in order to hang onto it.
Male House Sparrows fighting.
Photo by Jessica Lucia
Photo by Jessica Lucia
All that fighting takes a lot of time and energy, not to mention risk of injury. So the birds (and many other resource-defending animals) have found a less-dangerous shortcut: instead of fighting, they wear “badges of status,” color markings on their body that stand for how tough they are. Birds with less-tough badges don’t bother challenging the tougher birds, and everyone has to fight less. Sounds great, right? It’s the equivalent of a football player wearing a jersey that says “I’m Tougher Than You,” and the other football players just leaving him alone. So much less violent!
… but it doesn’t seem like it should work, does it? If it did, then anybody could put on a jersey that says “I’m Tougher Than Everybody” and win the Superbowl. What stops the birds from lying?
The birds of paradise have been getting a lot of attention lately for the elaborate courtship dances of their males, and nobody is going to argue that they don’t deserve it. But it isn’t all “males dance, females judge” in the avian world. The displays of male birds of paradise reflect high reproductive skew: a few males mate a lot, a lot of males never mate. It’s worth it to the males to devote incredible amounts of energy and resources to attracting females, because if they’re successful, they may sire many chicks. They can afford to spend all that energy and resources on crazy feathers and tricky dance moves because that’s all they have to do, parent-wise: they don’t help females build the nest or incubate the egg or raise the chicks.
Male Greater Bird-of-paradise. Photo by Ivan Teage.
But birds are diverse; the birds of paradise reflect just one point on a spectrum of mating systems. Near the other end are birds with low reproductive skew. Males of these species look pretty much like the females, and they contribute about equally to parental duties. You might expect that these species would lack dances the same way they lack meter-long curlicue tailfeathers, but some of them have dances every bit as formalized and elaborate as the birds of paradise. The difference is that these dances are duets.
Laysan Albatross pair performing courtship dance. Photo by Michael Lusk.
(Note on videos: I know clicking on videos is annoying. But it’s worth watching the videos in this post, I promise.)
Today’s discussion question is: why do the lovebirds Sam and Jesse spend a lot of time together?
Jesse and Sam pause in their destruction of a picture frame to wonder what business it is of yours how they spend their time.
“Well,” someone says, “it’s because lovebirds’ brain reward centers are stimulated when they interact with their mate. Happy molecules trigger happy receptors, and the birds get happy. So they seek out that reward.”
“No,” someone else says, “it’s because a lovebird that interacts with its mate more has a stronger pair bond, making it less likely to be cuckolded. Lovebirds who spend more time with their mates have more chicks and so pass more genes on to the next generation.”
Featured paper: Thanksgiving edition. And it’s doubly relevant – it’s about turkeys and family!
AH Krakauer. 2005. Kin selection and cooperative courtship in wild turkeys. Nature vol. 434, pp. 69 – 72.
Wild turkeys males show off in front of females in the hopes of being impressive enough to get to mate. While some males show off alone, others form “coalitions” of two to four males and all display for females together. However only one male in each coalition – the dominant male – ever gets to mate. So why in the world do the other male turkeys help him, if they never get to mate? Why don’t they display alone, where they’d at least have a chance at mating?
[Photo from Smart Kitchen]