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.
Claims that Ai Hin was faking pregnancy to get better treatment have been debunked by leading panda expert
The recent release of Susan Greenfields new book and the film Lucy, both of which are dependent on tired misconceptions or dubious theories about the brain, suggest one worrying conclusion: we are running out of myths about the brain. So here are some new ones, to keep things mysterious
These are the siphonophores, some 180 known species of gelatinous strings that can grow to 100 feet long, making them some of the longest critters on the planet. But instead of growing as a single body like virtually every other animal, siphonophores clone themselves thousands of times over into half a dozen different types of specialized cloned bodies, all strung together to work as a team---a very deadly team at that.
Researchers who study memory have had a thrilling couple of years. Some have erased memories in people with electroshock therapy, for example. Others have figured out, in mice, how to create false memories and even turn bad memories into good ones.
Hunting bats don't just listen out for male frogs' mating calls: they can also use echolocation to detect when the frogs inflate their throat sacs
A crèche of 30 dinosaur infants looked over by an older animal shows that even terrible lizards needed a night away from the kids
Families have identifiable collections of microbes that travel with them. It can take just 24 hours for the microbes to take over a new house
When rabbits were domesticated, around 100 regions of their genome changed to make them less fearful, but the variations are not fixed
Scientists never understood what became of the Paleo-Eskimos who once peopled the north. Now they know—and there's new reason to miss them
NOAA whittles down initial list of 66 species to be covered by Endangered Species Act