Let’s get one thing out of the way: All hummingbirds fight. Most species fight for food, using their tiny bodies and sharp bills to force competitors away from flowers. But the green hermit hummingbird, which lives primarily in mountain forests of Central and South America, fights to win a mate.

“They gather together at a place in the forest that looks just like a singles bar,” said , an associate professor of biology at the 91̽��. “They all have perches, and if someone else takes their perch — their place in the singles bar — they go bananas, and they fight.”

Hummingbirds’ weapon of choice? Their own bills. Like medieval knights in a joust, the birds raise a long, needle-thin bill into the air before driving it into their opponent. The stakes are high: Hummingbirds also use their bills to eat, poking them deep into flowers to reach nutrient-rich nectar. Losing a fight means a hummingbird might not find a mate. Breaking a bill could mean they starve.��

New research led by researchers at the , where Rico-Guevara is the curator of birds, found that these fights have shaped the species’ evolution, yielding significant differences in bill shape for male and female green hermits. Compared to their female counterparts, male green hermits’ bills are straighter, sharper and structurally stronger. The straighter bills work better as weapons, while female birds’ more curved bills provide improved access to nectar in some flowers. The findings suggest that green hermits’ bill sexual dimorphism — when two sexes of a species exhibit different characteristics — was likely driven by their tendency to fight, not solely by ecological factors.

“Adult male green hermits have reinforced bills because they fight so much,” Rico-Guevara said. “It’s the same tool, but in very different contexts. This is an example of how much we can still learn from sexual dimorphism in nature.”��

In the study, , researchers selected green hermit specimens from the Ornithology Collection at the Burke Museum and used to develop 3D models of male and female bills. Through curvature and angle analyses of those models, researchers found that male bills are 3% straighter and 69% sharper, respectively, with a dagger-like tip not found on female bills.

But the differences, researchers found, extend beyond bill shape. CT scans revealed that the male bill’s internal structure provided additional strength by transmitting forces more efficiently.��

Finally, researchers ran the models through a series of simulated stabbings to stress-test the bills in both head-on and angled attacks. They observed that the male’s straighter bill expends��52.4% less energy due to deformation, and is more resistant to breaking. The male bill experienced on average 39% less stress than the female bill.��

They also found that male bills’ straighter shape can accommodate a wider variety of attack angles, requiring less precision while fighting.��

“It’s a really cool example of sexually dimorphic weapons in birds,” said co-author , a graduate student at Michigan State University who completed this work while studying at the UW. “When you think of sexually dimorphic weapons, you usually think of deer and moose, animals with big antlers. There aren’t many examples of things like that in the bird world. It’s fun to explore a more cryptic or hidden weapon.”

Co-authors include of the Centro de Investigación Colibrı́ Gorriazul in Colombia and Ornithology Collections Manager at the 91̽��Burke Museum. This research was funded by a Walt Halperin Endowed Professorship at the 91̽��Department of Biology and by the Washington Research Foundation.��

For more information or to contact the researchers, email Alden Woods at acwoods@uw.edu.��

Why do humans wear clothes? One reason is that changing outfits allows people to tailor their look in hopes of attracting or avoiding attention. New research led by the 91̽�� found that hummingbirds may take a similar approach.��

It’s been known for some time that some — but not all — female white-necked jacobin hummingbirds take on the brightly colored plumage worn by males. In a study published a team of researchers from the 91̽��and Carnegie Mellon University have discovered the reason: They’re mimicking males. That trickery results in reduced aggression from other hummingbirds and increased access to nectar resources.��

“This research takes a mental model we’ve been describing for a while in our papers and gives it a mathematical backbone,” said , an evolutionary biologist who led this research while working as a postdoctoral scholar in the 91̽��biology department. “It can be easy to think of natural selection as a force that is constantly choosing one single optimum. But this model adds to our understanding of how diversity, especially diversity within sexes, can be a stable endgame.”��

Relying on the principles of game theory and incorporating previously collected behavioral data, the researchers developed a model of hummingbird behavior to better understand how some birds choose their colors. The findings showed that “hybrid signals” — an equilibrium that can occur when signalers in a given situation may be dishonest — likely exist in nature.����

“In these hummingbirds, females want to mimic males,” said Kevin Zollman, a co-author of the study and director of Carnegie Mellon’s Institute for Complex Social Dynamics. “If they all did that, then they would end up being disbelieved. So, they end up settling into an equilibrium where some of them ‘lie,’ and they are sometimes ‘believed.’”��

This mimicry helps explain how female polymorphism — in which females of a species can take many forms — persists among white-necked jacobins and other hummingbird species.����

“This model elegantly explains this puzzling female polymorphism in one species, but also offers a framework to study testable predictions of plumage differences, or lack thereof, between sexes across hummingbirds,” said , a 91̽��assistant professor of biology and co-author of the study. “We can use this to understand signals beyond plumage coloration, like different behaviors or body parts, such as long tails or auditory signals, which would entail different costs for the signalers and different model outcomes.”��

, a 91̽��professor of biology, is also a co-author. This research was funded by the National Science Foundation Postdoctoral Research Fellowship in Biology Grant, awarded to Falk, as well as the Walt Halperin Endowed Professorship and the Washington Research Foundation as Distinguished Investigator, awarded to Rico-Guevara. ��

This article is adapted from a press release by Carnegie Mellon University.����

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 published online Nov. 27 by the Proceedings of the Royal Society Interface, an international team led by , an assistant professor of biology at the 91̽��, 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 . “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.”

Co-authors on the study are , an associate professor at California State University, San Marcos; , a 91̽��assistant teaching professor of biology; independent researcher Jenny Hanna; , associate professor at Cornell University; and , a professor at the University of Cambridge. The research was funded by the Walt Halperin Endowed Professorship in the 91̽��Department of Biology, the Washington Research Foundation and U.K. Research and Innovation.

For more information, contact Rico-Guevara at colibri@uw.edu.

For the project, researchers teamed up with scientists at the Pontificia Universidad Javeriana in Colombia and officials at . The team hopes that data on small animals’ movements will inform plans to expand the park and connect it to other nearby protected areas.

Previously, it was impossible to collect movement data for hummingbirds and other small animals in the region. The team set up an automated radio telemetry grid in the , a high-altitude region in the Andes more than 10,000 feet above sea level. Their technology generates fine-scale resolution and continuous location estimates for individual animals, collecting in millions of data points that provide information on species’ habitat requirements, movement patterns and seasonal occurrence, all of which are critical for developing landscape-level management practices and avoiding local extinctions.

“Hummingbirds might not get the same buzz that bees do when it comes to the ecosystem services they provide, but they’re hugely important pollinators all the same,” said co-author , a 91̽��doctoral student in biology. “If you think about it in practice, it’s very challenging to protect an animal when you don’t know where or how far it moves each day, or what kinds of habitats it prefers. The fact that these questions are still largely unanswered when it comes to hummingbirds means that there remains a lot of important work to be done!”

The researchers used backpack-like harnesses to attach tiny transmitters to the hummingbirds. Since the birds themselves weigh at most about 10 grams, which is almost as heavy as an Oreo cookie, the transmitters had to be incredibly light – less than 500 milligrams, or the weight of a Tic Tac. The transmitter included a solar panel, providing it power for the bird’s lifetime. In early 2023, the researchers placed tags on 10 adult hummingbirds from two species, Great Sapphirewing and Bronze-tailed Thornbills, and followed the birds’ movements for up to 100 days.

“Through this, we have been able to obtain information on foraging routines, home ranges and seasonality,” said lead author , a graduate student at the University of Aberdeen. “This information increases our understanding about biodiversity in tropical mountains and is also useful to protect these species, as well as their key ecosystem roles as pollinators, in the face of ongoing climate and land use change.”

The study is the first to use automated radio signals in a high-mountain ecosystem to track the movements of animals, according to Rueda Uribe. It is also one of only a handful to try to track animal movements across terrain difficult for humans to trek across. The team plans to compare its findings about high-altitude hummingbird movements to data already collected by the team at the Colibrí Gorriazul Research Center, a separate mid-elevation site in the Andes.

The system prototyped in this study could easily be adapted to learn about small animals’ movements in other ecosystems, which directly impacts communities in the region.

“To know how to best conserve nature, we need to understand it fully, and this is opening the door to heretofore underexplored aspects of these small and elusive animals’ daily��choices,” said co-senior author , a 91̽��assistant professor of biology and curator of ornithology at the 91̽��. “This is especially important for the ��á�������� biome, which maintains water sources for other ecosystems down the mountains and for humans as well. It is a tremendous biodiversity hotspot that is comparatively less studied and much more threatened because of climate change and human-driven shifts in land use.”

Other co-authors on the study are María Ángela Echeverry-Galvis, professor at the Pontificia Universidad Javeriana; Pedro Camargo-Martínez of the Chingaza National Natural Park; of Queen’s University Belfast; and and , both professors at the University of Aberdeen. The research was funded by the U.K. Biotechnology and Biological Sciences Research Council, the U.K. Natural Environment Research Council, Walt Halperin Endowed Professorship at the UW, the 91̽��Orians Award for Tropical Studies, the 91̽��Margo and Tom Wyckoff Award, the National Science Foundation, the Rufford Foundation and the University of Aberdeen.

For more information, contact Rico-Guevara at colibri@uw.edu. ��

Adapted from a by the University of Aberdeen.

Many of us are familiar with the hummingbirds that visit feeders, plants and gardens around us. But these small creatures are unusual in the ways they push the limits of biology, says , 91̽��assistant professor biology and curator of ornithology at the . He and his students study hummingbirds and other birds that drink nectar.��

“I think what really caught my attention is their personality – how they can be so fierce and so bold despite being so tiny,” said Rico-Guevara.

Some of the smallest of all bird species are hummingbirds, and they are unique in the way they fly. They produce “lift” with the forward and backward motion of their wings, enabling them to hover in place for long periods of time, something no other bird can do. A giant hummingbird beats its wings around 10-15 times a second while some bee hummingbirds beat their wings over 100 times a second during hovering displays, using an incredible amount of energy. Hummingbirds have tiny legs and perch when they can, but their speedy metabolism requires them to visit flowers thousands of times and eat 1-3 times their weight daily in floral nectar. These pollinators also eat spiders, a good source of protein. To rest, they are one of few bird species that go into a sleep-like state called “torpor,” in which their metabolic functions slow to a minimum; while active, their heart beats around 600-1200 times a minute.

Hummingbirds have evolved so that they are well matched to the flowers they feed from. Their beaks can be long or short, curved down or even tilted slightly upwards to make them efficient at accessing nectar from specific blooms, and, perhaps, useful in fighting. They have become fast and nimble to out-maneuver other animals and insects for nectar, and hovering allows them to access the openings of hard-to-reach flowers.

Hummingbirds are fiercely protective of their food and will chase other birds away from flowers. They fly in front of each other and vocalize to scare each other off. Some hummingbirds will use their claws or bill to poke each other or pluck feathers. They’ve even been known to peck larger birds like falcons or crows, inspiring Aztecs to use hummingbirds as a warrior symbol. During breeding season, males court females with flashy displays of chirping, singing and aerobatics. Hummingbirds can make sounds with their tails and wings and learn new songs throughout their lives.

“It’s a circus,” said Rico-Guevara. “Their behavior is extremely rich.”

Advances in high-speed photography and lenses have made it possible to see bird activity that wasn’t possible a decade ago. Rico-Guevara has used slow-motion video to document the way that hummingbirds gather and swallow nectar, using a long, split tongue that flattens and springs open when it touches liquid, filling with nectar. describes how space inside the bill fills with nectar as the tongue is wrung out; then the tongue base rakes the nectar as it retracts. Pumping action through the flexible bill helps move the nectar towards the throat. These discoveries reveal a set of coordinated movements that are different and far more complex than what was previously believed – that hummingbirds drank by moving liquid through their tongues or bills using capillary action, much the way liquid will naturally move up a small glass tube.

“It’s all really complicated, and it’s happening up to 20 times a second,” said Rico-Guevara.

“It’s way more intricate than is known for any other bird.”

For more information, contact Alejandro Rico-Guevara / colibri@uw.edu

White-necked jacobin hummingbirds sport a colorful blue-and-white plumage as juveniles. When they grow into adulthood, males retain this dazzling pattern, while females develop a more “muted” palette of green and white — at least, most females. Curiously, about 20% of females defy the norm and retain male-like plumage into adulthood.

“Why do some female jacobins look like males? It’s a mystery made up of multiple pieces,” said , a postdoctoral researcher at the 91̽��. “Is there a benefit? Is there a cost? Is it just appearance, or do these females also act like males?”

Now those pieces are falling into place. In research Sept. 7 in the Proceedings of the Royal Society B, Falk and co-authors at the UW, Cornell University and Columbia University report that adult female white-necked jacobins with male-like plumage are mimicking male appearance — but not male behavior. In addition, their strength and body size are similar not to males, but to fellow females with muted plumage.

The study shows that the 1 in 5 adult females with male-like plumage are engaging in “deceptive mimicry”: They are essentially trying to pass themselves off as males, without acting like them. In the process they receive quite a benefit. As Falk and his colleagues in a published last year in Current Biology, females with male-like plumage suffer less aggression from males compared to females with the more typical muted plumage, and can hang out longer at feeders.

Falk began this research as a graduate student at Cornell University and continued it as a postdoctoral fellow with co-author , a 91̽��assistant professor of biology and curator of ornithology at the UW’s .

White-necked jacobins are common in tropical lowlands of the Americas. Males of this species, put simply, are bullies. They defend territories, chase rivals away from food sources, court females and fight. That aggressive behavior relies on an underlying difference in body size and physiology: Male jacobins are larger and are better at combative flight compared to dull-colored females.

An unanswered question from Falk’s previous study was whether females with male-plumage also displayed male-like flight power or behavior. At a field site in Panama, he briefly captured male jacobins and females with both types of plumage. He discovered that females — regardless of plumage — had essentially identical body and wing sizes, whereas males were slightly larger. Before releasing the birds, Falk also tested their “burst power” — or muscle capacity during flight — by seeing how high they could fly while lifting a chain of small, weighted beads. Females of both types of plumage had identical burst power, while males could lift more on average.

Using data from radio-tagged birds in the wild, the team also discovered that more males fed in a “territorial” pattern — spending longer amounts of time at a smaller number of feeding sites. All females, regardless of plumage, showed the opposite pattern: feeding for shorter periods of time at sites across a larger territory.

“Females with male-like plumage don’t seem to be behaving any differently than other females,” said Falk. “All evidence instead indicates that females that look like males are engaging in deceptive mimicry.”

Many examples of deceptive mimicry occur between species: a harmless species will mimic the coloration of a noxious species as an anti-predator defense. In the Americas, for example, some non-venomous kingsnake species have evolved colorful banding patterns that resemble venomous species in the same area, such as coral snakes. showed that this deceptive mimicry decreased predation of the kingsnakes, which are not venomous. What Falk and his colleagues found in white-necked jacobins appears to be an example of deceptive mimicry within a species.

Scientists have reported females with male-like plumage in other hummingbird species. If so, male mimicry within hummingbird species may be more common than currently known. Next year, Falk will move to the University of Colorado Boulder to study the genetic differences between females with muted and male-like plumage — and potentially identify how this deception evolved.

But differences between the sexes are not the whole story.

“Even when I found average differences in female and male morphology, burst power or behavior, I also found quite a bit of overlap between the sexes,” said Falk. “That indicates that sex isn’t the only important factor, and that variation among and between individuals plays an important role.”

Falk and Rico-Guevara are currently studying the role of individual variation in these traits, regardless of sex.

Additional co-authors on the study are Michael Webster of Cornell University and Dustin Rubinstein of Columbia University. The research was funded by Smithsonian Tropical Research Institute, National Science Foundation, Cornell University, the Walt Halperin Endowed Professorship at the UW, the Washington Research Foundation, the Society for the Study of Evolution and the American Society of Naturalists.

###

For more information, contact Falk at jjfalk@uw.edu.