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A male Satin Bowerbird is just completing construction of his bower — a sort of dance floor — two walls of vertical dry grass stems with a lane between them. (Think of two book ends close together.) He’s constructing the bower from small twigs and dried grass stems that are intertwined vertically. He knows that a well-constructed bower can help him attract a mate. He wants to entice a female to enter the bower lane and watch his song and dance. He grabs a twig that is leaning into the center, pulls it out, and pushes it down again into a more vertical position. There, much better. Now, he removes leaves and twigs from inside and in front of the bower so all is neat. But he’s not finished.
Most male bowerbirds decorate their bower with artifacts such as berries, flower petals, feathers, even plastic bottle caps. Such artifacts can also stimulate a female, but they must be of the right color — specific to each species. In the case of the Satin Bowerbird, the color of choice is blue. In anticipation of a female, the male hurriedly rearranges the blue artifacts, as if they must be perfect. He grabs a feather and drops it closer to the bower, then picks up a blue bottle cap and drops it closer to the feather. Still hurrying, he repositions several blue flowers.
At last, a female comes to the bower and walks in from the backside. Female Satin Bowerbirds commonly inspect bowers when males are not present. Maybe she was here before and liked it. Now she is back to judge him. If several males build their bowers in the same general area, females can evaluate males more quickly and watch them all as their bowers take shape.
A female in his bower means he’s passed the first test — she’s going to give him a closer look. It’s as if she’s shouting, “Bring it on!” The male hurries to the bower, not at the open lane but slightly stage left or right, so he can dance and sing past the lane opening. With head down, he snaps his wings up and down, along with his tail; then, with head up, he sings at the top of his lungs and dances across the opening.
He turns and comes back with high-intensity “buzz-wing flips.” He quickly bends his legs and straightens up, pumps his tail, does a pirouette, and rapidly flaps his backward-pointing wings in a blur. In a jerky fashion, he jumps close to the bower, and the female backs out. He must control the intensity of his displays — too strong, and he can drive her away; too timid, and he won’t stimulate her enough. Now she’s back. He watches her actions. She starts to stomp her feet and flap her wings, which excites him even more, as she is buying into his message.
The male senses that she is ready to mate and runs to the back of the bower, enters the lane, moves up, and mounts her. A flurry of wing beating and tail movement for just a few seconds, and it’s over. Sperm is transferred. The assortment of behaviors, refined through eons of natural selection, worked. If the female hadn’t been properly stimulated when the male went around the bower, she would have left to go and check out the bowers of other males.
Some females, especially younger ones, select males on the basis of bower construction and decoration (they are often intimidated by aggressive males), while others, mostly older, consider the males’ song and dance skills. Over time, females may change the criteria they use for choosing a mate, thereby requiring that successful males must refine critical and distinctive behaviors — building and design, and song and dance. That females require males to perfect two different selection pathways is highly unusual.
Bowerbirds are long-lived, and females remember the bower locations of choice males. So older females often go directly to a known male’s bower, without needing to evaluate the bowers of others.
A second type of bower, called the “Maypole,” consists of a circular runway around a narrow tree sapling or several saplings. Twigs and sticks are stacked around the sapling, and plant material, including mosses and lichens, rings the outside of the runway. It’s an oval racetrack.
An interested female will join the male on the runway, but on opposite sides of the sapling. The male displays and sings while they both move around the circle. If the female is interested in mating, she will appear agitated, with quick body movements, but will slow down, allowing the male to catch up so mating can occur. But if the male judges her interest incorrectly, she’s gone.
From the intricate design of bowers to frenzied song-and-dance routines, the courtship behavior of bowerbirds is astonishing to behold. It once again reminds us of the amazing behavior of birds.
Eldon Greij’s column “Amazing Birds” appears in every issue of BirdWatching magazine. This article appeared in the March/April 2018 issue. Eldon is professor emeritus of biology at Hope College, located in Holland, Michigan, and the founding editor of Birder’s World magazine.
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