如何绘制蜂鸟花蜜?

如何绘制蜂鸟花蜜?这个微小的红嘴绿宝石蜂鸟(Chlorostilbon gibsoni)提要千花了一天。 Kristiina Hurme,CC BY-ND

蜂鸟在艰涩的速度鲜活的生命。 他们的飞行杂技是惊人的,机动 更像昆虫的鸟类比 因为他们身边掠过,飞倒挂,甚至倒退。 他们是因为他们花间的竞争一片模糊。 当他们停下来短暂访问的花,它们舔15 20到次第二,以提取其花蜜的燃料。

是什么让他们如此有趣的给我们的是这样简单的饮食选择的结果:他们喝花蜜。 每朵​​花不提供很多,所以为了生活,将整个森林微量花蜜传播,蜂鸟是微小的,速度快,争强好胜。

取食花蜜是蜂鸟'定义特征,但直到现在科学家们不知道他们是如何做到这一点的确切机制。 在我们的新研究中,我们能慢下来的视频看到 怎么他们真的喝花蜜。 而我们发现来自以来1800s传统观念有很大不同。

管饲?

蜂鸟'瘦舌头大约相同的长度他们的账单。 他们完全适应了深远深成一朵花。 在过去的几年180科学家认为,喝花蜜,蜂鸟依靠毛细管作用。 当时的想法是,他们的舌头会在一个小玻璃管水被动填补了同样的方式填补花蜜。

毛细作用的物理依赖于两股力量。 液体分子的管壁的粘附使得液体爬上两侧。 表面张力保持在一起的液体和向上拖动整个流体柱。

hummingbird lick2A hummingbird’s long skinny tongue has two grooves running down the middle, and ends in a forked tip that spreads inside the nectar. Alejandro Rico-Guevara, CC BY-NDThe capillary action theory made sense since a hummingbird’s tongue has two tube-like grooves. It would be a simple, passive way for nectar to travel up the tongue.

Hummingbirds Are Faster Than That

But from watching hummingbirds in my (Rico-Guevara’s) native Colombia, we felt that capillarity just wasn’t fast enough to keep up with how hummingbirds feed. We predicted that capillarity was too slow to account for the fast licking rates observed in free-living hummingbirds. Remember, they can drain a flower’s nectar with around 15 licks in under a second!

Four years ago, one of us (Rico-Guevara) and colleague Margaret Rubega challenged the conventional beliefs about capillary action for the first time. We showed that the forked tongue tips are not static, but dramatically spread inside the nectar, with fringed edges that open up like tiny hands. When the hummingbird retracts its tongue from the nectar, these fringes close due to the physical forces of surface tension and Laplace pressure, trapping nectar drops in their grips. Due to this transformation of the tongue shape, the tongue tips don’t remain in the tube-shape necessary for capillary action.

So how does the rest of the tongue fill with nectar?

We set out to study a medley of hummingbird species to see what these birds were really doing at the flowers. We needed a way to measure a tongue’s thickness during the drinking process – straightforward, but not an easy task.

We designed see-through artificial flowers that we filmed with slow-motion cameras. From these videos, we could then track the shape of the tongue throughout the whole licking cycle. The difficult part was convincing wild hummingbirds to drink on command. Over time, we trained them by habituating them to the phony flower feeders and our whole filming setup.

Science Discovery Via Slow Motion Video

When a hummingbird inserts its bill into a flower, it still needs to stick its long tongue deeper inside to get at the nectar within. After the tongue fills with nectar, the bird retracts the tongue back inside the bill. Researchers already knew that to keep the nectar inside the beak, the hummingbird squeezes the tongue with the bill tips as it is extended for the next lick. That compresses and flattens the tongue on its way out, leaving the nectar inside the bill. The way in which the nectar is moved from the bill tip to where it can be swallowed remains unknown.

To study the tongue-filling mechanism, we focused on the flattened shape of the tongue that each lick starts with. If the hummingbirds were using capillarity, once the nectar had made it into the bird’s mouth, the tongue would immediately need to recover its tube-like shape before touching the nectar again.

By closely studying our slow motion videos of the birds drinking at the transparent flowers, we saw that the tongue remained flattened after the squeezing even as it traveled through the air to reach the nectar for another sip. It didn’t snap back to its original pre-drink tube-like shape.

We studied 18 hummingbird species, and in hundreds of licks, we found that the tongue remained flattened until it touches the nectar. This was a key finding because it showed that the tongue didn’t have the empty space inside needed for capillary action to work. Finally, we can confidently rule out capillarity as important for hummingbird drinking.

How They Really Pump The Nectar In

What we found goes beyond simply debunking capillarity. Hummingbirds have hit on an unexpected way to move liquid very quickly at this micro-scale: their tongues are elastic micropumps.

The grooves in the hummingbird tongue don’t reach the throat, so the bird cannot use them as tiny straws. For this reason, instead of using vacuum to generate suction – imagine drinking lemonade out of a straw – the system works like a tiny pump, powered by the springiness of the tongue. The bird squashes the tongue flat, and when it springs open, this expansion rapidly pulls the nectar into the grooves in its tongue. It turns out it’s elastic energy – potential mechanical energy stored by the flattening of the tongue – that lets hummingbirds collect nectar much faster than if they relied on capillarity.

While the tongue moves through the air, the elastic energy loaded into the groove walls during the flattening is conserved by a remaining layer of liquid inside the grooves acting as an adhesive. When the tongue touches the nectar, the supply of fluid allows the release of the elastic energy which expands the grooves and pulls the nectar to fill the tongue.

0316817155As a hummingbird drinks, each lick collects nectar, while rapidly preparing the tongue pump for the next lick. Alejandro Rico-Guevara, CC BY-NDAs biologists, we were excited by this new discovery, but needed the help of an expert in fluid dynamics, Tai-Hsi Fan, to accurately explain the physics of this hummingbird micro-pump, and to make new predictions.

Our research shows how hummingbirds really drink, and provides the first mathematical tools to accurately model their energy intake. These discoveries will influence our understanding of their foraging decisions, ecology and coevolution with the plants they pollinate.

Our ongoing research compares our new model with how much nectar hummingbirds drink at wildflowers, and looks at the trade-offs between drinking efficiently and fighting for dominance over territories either to attract females, to feed, or both.

关于作者谈话

rico gueva alejandroAlejandro Rico-Guevara is Research Associate in Ecology and Evolutionary Biology at University of Connecticut. He is a functional morphologist using nectar-feeding birds as a study model to bridge the gap between our knowledge of ecological and coevolutionary patterns and their underlying mechanisms. More at alejorico.com

Kristiina Hurme is Research Associate in Ecology and Evolutionary Biology at University of Connecticut

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