How flowers have evolved particular colours, shapes and scents to attract pollinators has long fascinated ecologists. Now, using artificial flowers and high-speed video, researchers have gained intriguing insights into the intimate relationship between hummingbirds and the flowers they pollinate. The study, published in the British Ecological Society's journal Functional Ecology, is the first to measure how much energy hummingbirds use while hovering to feed from flowers of different orientation.
Hummingbirds are among the smallest and most brightly-coloured birds on Earth, and one of the only types of bird capable of hovering for long periods. They are also crucial pollinators of flowering plants across the Americas. Hummingbird-pollinated flowers are usually red, tubular-shaped and have no smell, characteristics that have been well-studied by ecologists. Why most hummingbird-pollinated flowers hang down vertically, however, has remained a mystery.
Working with Anna's hummingbirds (Calypte anna) – the most common hummingbird species on their university campus – Dr Nir Sapir and Dr Robert Dudley of the University of California, Berkeley built a series of artificial "flowers". The artificial flowers, which pointed horizontally, vertically-downwards or were tilted 45 degrees downward, supplied nectar to the birds.
After training the hummingbirds to feed from the artificial flowers, the researchers used high-speed video to record how flower orientation affected the birds' body position and hovering style while feeding. They then fitted the artificial flowers with a mask to measure the amount of oxygen – and hence how much energy – the birds used to hover while feeding.
The results revealed that to feed from flowers hanging down vertically, the hummingbirds had to adopt a "bizarre" body position, with their bodies upright and heads bent back, and that doing so required 10% more energy than feeding from horizontal flowers.
The results are intriguing, says Dr Sapir: "Because flowers need pollinators to reproduce, flowers have evolved to attract pollinators. Almost all hummingbird-pollinated flowers hang down vertically, so our hypothesis was that they evolved this way because hummingbirds would have to use less energy to feed from them. We found the opposite – that it's more costly in energy terms for hummingbirds to feed from these flowers."
In evolutionary terms, this means other factors must be at play. "Our findings suggest other factors may be dictating flower orientation. Flowers may need to exclude less efficient pollinators, such as insects, and so flowers that hang down vertically may be selected during evolution to increase pollination efficiency. And horizontal flowers are more exposed to rain, which can dilute the amount of nectar in a flower, and we know that hummingbirds can tell how sweet nectar is, so they may select downward-facing flowers because their nectar is less diluted by rain and thus contains the most sugar."
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Free-living songbirds show increased stress hormone levels when nesting under white street lights. But different light spectra may have different physiological effects as this study finds, suggesting that using street lights with specific colour spectra may mitigate effects of light pollution on wildlife
Scientists identify the condition aphantasia, in which people cannot create images in their head
The dust in our homes contains an average of 9,000 different types of fungi and bacteria, a study suggests.
A mosquito can bear up to 23 times its total body weight on each leg, which is crucial for landing on water – the insect's secret is way it stands
Tropical species with smaller geographical ranges are more likely to die out in a warming climate than those that can adapt by ‘invading’ new regions
Most people think of bacteria as germs, signs of filth, or unwanted bringers of disease. Slowly, that view …
The gloomy octopuses crowded at Jervis Bay, Australia, appear to spit and throw debris such as shell at each other in what could be an intentional use of weapons
Therapies based on hormones that make us more trusting enhance our natural placebo effect – a finding that could alter the way clinical trials are conducted
The blind, hairless babies born recently at Washington D.C.'s National Zoo are completely dependent on their mothers—who can sometimes accidentally crush them.
The poop-hoarding insects have an amazingly advanced internal GPS that allows them to navigate by day or night.