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The flight of hummingbirds -

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Robyn Williams: We mentioned hummingbirds just then, delightful creatures who turn out to have very sophisticated vision, only now being understood through experiments at the University of British Columbia and Queensland. This is Douglas Altshuler, with Ben Goller, at the Department of Zoology there.

Douglas Altshuler: People often think that it is the great speed with which they flap their wings, because most of them do flap their wings very quickly. The smallest hummingbirds hover with wingbeat frequencies up to around 80 times per second. And even the ones we have in North America flap quite fast, around 30, 40, maybe up to 50 times a second. But there is one hummingbird that puts really a monkey wrench in this idea, and that's the giant hummingbird. There's a hummingbird in the high Andes of South America that weighs up to 26 grams. That's about six times larger than most of the hummingbirds we have here. And it flaps its wings at about 14 times a second. That is actually quite smaller than, say, an Australian zebra finch. So here we have a hummingbird hovering perfectly well, but doing so with a pretty slow wingbeat frequency.

Robyn Williams: You said hummingbirds here in Canada, you've got them in Canada?

Douglas Altshuler: That's right, we actually do have a number of species in Canada. Some of them have been here a while. The Rufus hummingbird, that has the largest migration of any hummingbird, so it spends its winters down in Mexico, and it summers all the way up to Alaska. So there are some of them that reside here during the summer, and there are some that just pass through on their way up north.

But in addition to that we have a hummingbird we are very excited about having here, which is called the Anna's hummingbird, a mostly non-migratory hummingbird that has been in the southern US, around California, and its northern range limit used to be in Oregon, but over the last 20 years that northern range limit has expanded all the way such that there are now year-round populations in Vancouver and other parts of southern British Columbia.

Robyn Williams: Benny, given the fact that you don't really have an explanation about the flying, what did you investigate?

Benny Goller: Well, the nice thing is that the hummingbirds hover, and so they do that so that they can sip nectar from a flower. And so I set out with the idea of let's see how they interact with that flower, and let's show them visual patterns that move, let's puff gusts of air at them, let's just try and disrupt that delicate interaction with the food source.

Robyn Williams: Oh, poor thing! But I've seen the video that you've done where they come down and they hover, and they are almost still in the air, with the beak actually down a tube, it's a glass tube, resembling the flower, and it's as if they just move down, stay still, suck, and then move off. So what happened?

Benny Goller: That's when the background is either blank or stationary. And what you can do is then…because it's a projection produced by a computer, you can start to move the patterns. And what we found is that when the background appeared to approach the hummingbird, the hummingbird would start to slide backwards, recover its position, put its bill back in the flower and then slide backwards again. And if you now reverse that so that the background appears to be falling away, the hummingbird just flies forward as far as it can, jams its bill into the tube. And the same is true if you are moving the pattern left-right, up-down, or a combination of those directions.

Robyn Williams: Because you'd think that it was simply concentrating on what's in front of its face rather than the background.

Benny Goller: Yes, that's what I sort of expected would happen, but it actually seems to follow what's going on in the background very closely, at the cost of the flower itself.

Robyn Williams: Interesting, isn't it. Doug, what can you learn therefore from this question of background that tells you about its general perception of what's going on?

Douglas Altshuler: What we've done in this case is we've used a behavioural test—how does a hummingbird feed from a flower in the presence of moving images—to try and gain some insight into how the brain is actually working. And so one of the things we now know is that these hummingbirds with their visual system are paying a lot of attention to the global background, which is to say they are monitoring images over a very wide range, and then now what we want to do is understand how that is actually happening at the level of the brain and understand why it is that they have to pay attention to such a wide range of images.

Robyn Williams: When you think about it, you talked about the migration, of course one minute it's looking at this solitary flower, the next minute you say it's moving across the landscape, different kinds of flight, different kinds of perception, is that right?

Douglas Altshuler: That's exactly right, and in fact that is the question that is motivating this project that we have in collaboration with Mandyam Srinivasan at the Queensland Brain Institute. Together we are studying different bird species, and what we want to understand is how do birds use vision to guide their flight in different contexts. So think about things like cruising flight when they are moving forward versus hovering flight when they are stationary, and also how they transition between these different flight modes.

Robyn Williams: Well, Srinivasan is a person world famous for bees, so he's working on birds as well?

Douglas Altshuler: That's right, over the last few years he has become interested in bird flight, which was very exciting for us because he has always been a great hero of mine. And through his new interest in bird flight, this presented an opportunity for us to work together.

Robyn Williams: Yes, the question is whether the perception of the landscape is the same, because he has done tremendous work on the way bees learn quickly, amazingly enough, from what's around them and how they learn to go to and from.

Douglas Altshuler: Well, it's interesting, we have not focused as much on learning, which, as you rightly say, a lot of Srinivasan's work has been about the waggle dance and how distance is understood by these foragers and how it's then communicated to other members of the hive. But one of the other things that Srinivasan has studied a lot of is how insects use visual information to determine things like distance, and also to determine where they should be in a narrow passage, should they fly nearer the wall or away from the wall. And what we've been finding so far is that there actually are many similarities between how honeybees guide their flight and how birds guide their flight. This is actually despite the fact that their brains are completely different.

Robyn Williams: Totally.

Douglas Altshuler: Totally different, that's right, they are completely different brains and yet they have actually converged on many of the same strategies.

Robyn Williams: Benny, a personal question, working with hummingbirds, beautiful animals aren't they.

Benny Goller: They are great to work with in the lab. They are quite easy to train. It's very helpful that you have an animal with a metabolism as fast as a hummingbird's. You can get them to come to a feeder on a 10- or 15-minute cycle, and they will jump through hoops for you to get to that sugar water. Otherwise they are obviously just fun to have around and to film. It's great.

Robyn Williams: Being tiny, do they respond to you at all?

Benny Goller: Yes, they do, and different birds all respond differently. Some of them show absolutely no fear and will get in your face, and other ones are a bit more skittish, but overall they are great to work with in the laboratory.

Robyn Williams: Doug, a final question, just to expose my ignorance; we don't have any in Australia, do we?

Douglas Altshuler: No, that's right, hummingbirds only exist in the new world, in the western hemisphere. And it's funny, one of the questions I often get in talks is someone says to me something like, oh, I saw this great hummingbird when I was in New Zealand or when I was in Australia or when I was in Europe, and I always have to do correct them politely and say, um, no, actually that was not a hummingbird. But it turns out there are species of moths that look a lot like hummingbirds and also hover and can easily be misidentified as a hummingbird.

Robyn Williams: Professor Doug Altshuler and Ben Goller at the University of British Columbia.


Guests
Douglas AltshulerAssociate Professor of Zoology
University of British Colombia
Vancouver BC CanadaBenny GollerPhD Candidate
Department of Zoology
University of British Colombia
Vancouver BC Canada

Further Information
Douglas Altshuler at UBCBenny Goller at UBCHummingbirds by Maureen - photos of Hummingbirds

Credits
PresenterRobyn Williams ProducerDavid Fisher