[00:00.00]Listen to part of a lecture in a biology class.
[00:03.64]Biologists study complex animal behaviors to find out why these behaviors evolved, how they function, how they're transferred to the next generation and so forth. [00:14.15]The courting behavior of the Bower bird is studied for all these reasons. [00:18.90]A Bower bird is about the size of a pigeon and found mostly in Australia's rainforest, which is a small but ecologically diverse area in northeastern Australia. [00:28.78]Bower refers to the male birds nest or structure. [00:33.05]Now, most birds, including female Bower birds, build nests to raise chicks, but male Bower birds build elaborate structures to help them attract mates.
[00:43.70]Take a look at this Bower bird decorating the outside of his structure. [00:47.44]As you see, construction takes place on the forest floor, not in a tree. [00:52.68]Apparently, the female Bower birds like blue decorations. [00:56.89]The male decorates the bower with feathers, flowers, pebbles, and shells. [01:01.68]We found Bowers decorated with bright blue clothes pins, probably snatched from someone's backyard. [01:07.50]Bower birds are also known to steal ornaments from other Bower birds. [01:11.54]When the Bower is ready, a female bird may come over to it and watch the male perform for her. [01:16.97]He'll dance, singing or rather chirp, often quite energetically.
[01:21.82]Okay. There is 17 different kinds of Bower birds all classified by the type of Bower they build. [01:29.78]And there are three major types of Bower. [01:32.61]First is the mat Bower. [01:35.99]Mat Bowers are the least elaborate and the easiest to build. [01:39.83]They're basically thick pads made from sticks and leaves surrounded by ornaments. [01:45.05]With mat Bowers, there's no real shelter for the female. [01:48.06]So when the males are doing their performance, they keep their bellies close to the ground, signaling they will not attempt to mate unless invited to do so. [01:57.20]And in this way, they don't frighten or overwhelm the female. [02:01.07]Next is the maple bower. [02:05.09]And maple Bowers are built around a small tree, a sapling. [02:09.37]But they sometimes have two towers of twigs with a little covered bridge between them. [02:14.74]Maple Bowers often have a moss lawn, which is kept neat and fresh.
[02:20.45]Now, the most elaborate Bower is the avenue Bower, like the one you saw in the slide. [02:27.76]First, the bird constructs an avenue, which is like a tent out of twigs, and then it places ornaments all around it. [02:35.34]The female can actually go into this Bower to watch the males performance. [02:39.80]And we believe that Bowers generally and especially avenue Bowers, provide protection for the female protection against unwanted mating, perhaps. [02:49.14]Or so, she won't feel threatened during the courting dance. [02:52.58]And the male may even paint the inside walls of his Bower. [02:57.80]He paints with saliva, saliva mixed with chewed up blueberries along with charcoal. [03:03.77]Let's consider the factors that drive male Bower birds to create these structures.
[03:09.61]One biologist Gerald Borgia has been studying Bower birds for more than 20 years. [03:15.39]Borgia found, well, first we call that many bird species select their mates based on the attractiveness of their feathers or plumage. [03:24.08]Peacock, a prime example. [03:26.30]One biologist hypothesized that the Bower birds that built the most elaborate Bowers had the least colorful plumage, but Borgia has disproved that hypothesis. [03:37.24]He found no significant relationship between dull feathers and fancy Bowers. [03:42.20]Borgia has found differences in the Bowers based on where they're located. [03:47.08]The fanciest one is tend to be in valleys as opposed to hill tops. [03:51.176]He thinks this has something to do with the available light. [03:54.49]Hill tops are often cloud covered, so females can't see the Bowers very well in the valleys, though there's more sunshine. [04:01.87]In another study, they found that 75 % of females returned to the same mate year after year and visit no other Bower.
[04:10.64]You have to wonder why the males would go to such trouble every year, you know. [04:15.78]Uh it, especially since there's no guarantee, especially for young males that any female will choose them. [04:22.03]But who knows? Maybe one of you will shed some light on this one day. [04:26.92]Bush is also very interested in finding out whether bowerbird behaviors are learned from their elders, or whether these behaviors are encoded in their genes at birth, like painting. [04:38.21]Do they learn to paint by watching another male bird? [04:41.60]Or do they just know how to do it? [04:43.72]To figure this out, Borgia is raising some male Bower birds in captivity. [04:48.12]Some with older birds to learn from and some without.
托福14天冲刺微信战团