Hummingbird bills — their long, thin beaks — look a little like drinking
straws. The frenetic speed at which they get nectar out of flowers and backyard
feeders may give the impression that the bills act as straws, too. But new
research shows just how little water, or nectar, that comparison holds.
In a paper published
online Nov. 27 by the Proceedings of the Royal Society Interface, an
international team led by Alejandro Rico-Guevara, an assistant
professor of biology at the University of Washington, reveals the surprising
flexibility of the hummingbird bill. The team discovered that a drinking
hummingbird rapidly opens and shuts different parts of its bill simultaneously,
engaging in an intricate and highly coordinated dance with its tongue to draw
up nectar at lightning speeds.
To human eyes, these movements are barely perceptible. But for
hummingbirds, they’re a lifeline.
“Most
hummingbirds drink while they’re hovering mid-flight,” said Rico-Guevara, who
is also curator of ornithology at the UW’s Burke Museum of Natural History and Culture.
“Energetically, that is very expensive. Flying straight at commuting speeds
uses up less energy than hovering to drink. So, hummingbirds are trying to
minimize energy and drink as fast as they can — all from these hard-to-reach
spaces — which requires special adaptations for speed and efficiency.”
Previous research showed that hummingbirds extend their tongues in
rapid-fire movements when drinking nectar. But scientists did not know what
role the bill itself played in feeding. The team collected high-speed video
footage of individual hummingbirds from six different species drinking at
transparent feeders at field sites in Colombia, Ecuador and the U.S. By
analyzing the footage and combining it with data from micro-CT scans of
hummingbird specimens at the Yale Peabody Museum, researchers discovered the
intricate bill movements that underlie drinking:
·
To extend its tongue, the
hummingbird opens just the tip of its bill
·
After the tongue brings in nectar,
the bill tip closes
·
To draw nectar up the bill, the
hummingbird keeps the bill’s midsection shut tightly, while opening the base
slightly
·
Then, it opens its tip again to
extend the tongue for a new cycle, a process many hummingbird species can do
10-15 times a second
Hummingbirds have intricately shaped tongues, some resembling origami-like
patterns for unfolding and collecting nectar. This new research shows just how
important the bill is for drinking and that, despite its rigid outward
appearance, it is remarkably flexible.
“We already knew that hummingbird bills have some flexibility, for example
bending their lower bill while catching insects,” said Rico-Guevara. “But now
we know that the bill plays this very active and essential role in drawing up
nectar that the tongue collects.”
The bill’s role also makes hummingbirds unique among animals by relying on
two types of fluid collection and transport methods: the lapping mechanism —
formally known as Couette flow — which animals like dogs and cats use to drink,
and Poiseuille flow, a suction-driven mechanism used, for example, by
mosquitoes drinking blood or by humans drinking through a straw. Often, animals
employ one approach or the other. Hummingbirds are a rare example of using
both.
“It makes sense that they would have to use both, given the pressure to
reach the nectar deep within the flower and to feed quickly and efficiently,”
said Rico-Guevara.
Future research could try to find the muscles that control these movements,
and investigate how other uses for the bill — such as catching insects — impact
its flexibility.
“As plants evolved flowers of different lengths and shapes, hummingbird
bills have evolved accordingly,” said Rico-Guevara. “Every time we answer one
set of questions about hummingbird adaptation, new ones arise. There’s so much
more to learn.”
Source: https://www.washington.edu/news/2024/12/05/how-hummingbirds-drink/
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