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Hummingbirds: Dazzling and Diverse

The remarkable behavioral and anatomical features of hummingbirds are the same things that make them so endearing to us.

DATE:
September 20, 2020
Author
Ivan Phillipsen

Key Traits of Hummingbirds

It’s an understatement to say that hummingbirds are charming. They’re captivating and fascinating. Just about everyone loves them. And if you don’t love hummingbirds, something is probably wrong with you, and you should seek professional help.

The remarkable behavioral and anatomical features of hummingbirds are the same things that make them so endearing to us. 

Let’s review those features.

First off, hummingbirds are small. Really small. Most species are between 3 and 5 inches long (7 to 13 centimeters). That’s from the tip of the bill to the end of the tail. 

At the two ends of this spectrum, within the hummingbird family, are the Bee Hummingbird at 2.2 inches long and the Giant Hummingbird at about 9 inches.

Giant Hummingbird in Ecuador.
Giant Hummingbird in Ecuador. Photo by Ivan Phillipsen.

The Bee Hummingbird, which lives in Cuba, is actually the smallest bird in the world. This tiny beast weighs less than a standard Lincoln Penny or less than a 1 Euro cent coin.

Besides being super small, hummingbirds are famous for their flying abilities. Their wings beat so fast and in such a way that these birds can hover, holding themselves stationary in the air.

This ability helps hummingbirds easily feed from flowers, which is also one of their key features. They are specialists that drink flower nectar.

And last, hummingbirds are colorful and shiny. We like shiny things. Males of many species sport patches of iridescent feathers, which reflect sunlight as an array of sparkling colors.

So, hummingbirds are small, colorful nectar-feeders that have amazing flight abilities. I’m going to dig more into each of these key features in a bit. But first, let’s discuss the evolution and diversity of these birds.

The Evolution of Hummingbirds

Hummingbirds all belong to the biological family known as Trochilidae. The root of this name is the Latin trochilus, meaning a small bird.

The cousins of hummingbirds—that is, the avian families most closely related to the hummingbird family—are the swifts and treeswifts. The common ancestor of hummingbirds, swifts, and treeswifts lived between 40 and 50 million years ago.

Scientists think this ancestral bird lived somewhere in Eurasia. In 2004, several hummingbird fossils were discovered in Germany. That’s right, Germany. They were dated to about 30 million years ago, which makes them the oldest known hummingbird fossils. This was a crazy discovery because hummingbirds today are found only in the Americas. Prior to 2004, it was assumed that they had originated in the “New World.”

One of the early evolutionary innovations of hummingbirds was the ability to taste sweetness. Most birds don’t have a strong sense of taste, as far as we know, and most can’t detect sweetness. 

Research has found that the receptor for sweetness in hummingbirds evolved from mutations in a gene that allows other birds, ranging from chickens to swifts, to taste savory, protein-rich things. Things like bugs. Mutations in that gene made it much easier for hummingbirds to assess the sugar content of flower nectar. This allows them to assess the relative amount of its life-giving caloric energy.

So, wherever they originated in the world— again, probably in Eurasia— hummingbirds eventually made it to the Americas by about 22 million years ago. That’s when their evolution went into overdrive.

The wide open habitats, landscapes, and isolated islands of the Caribbean, Central America, and South America offered countless opportunities for local adaptation and diversification in hummingbirds.

The explosion of new species formation in this region is an example of what we call an adaptive radiation. This is where many species evolve from a single common ancestor in a relatively short time, at least in geological terms. The catalyst for this process is the availability of numerous empty niches, such as occurs when a species lands for the first time on a group of isolated islands. 

Over the last 22 million years, this adaptive radiation has resulted in 12 genetically distinct hummingbird lineages and there are now over 300 species. 

Genetic studies of hummingbirds show their evolution is still rocking and rolling at this very moment. They continue to diversify, which means more hummingbird species are coming into existence. And that means there will be more and more happiness in the world.

The likely secret to hummingbirds’ evolutionary success is their close relationship with flowering plants. Flowering plants are insanely diverse. In a dynamic process called coevolution, a hummingbird and the plant it feeds on both adapt to each other over millions of years. The plant comes to depend on the bird to spread its pollen from flower to flower, and the bird depends on the rich nectar offered by the plant. The hummingbird's bill shape evolves to match the shape and depth of the flower, just as the flower evolves to accommodate the hummingbird by being more attractive and providing access to the reward of its nectar. 

A plant that co-evolved with birds in this way is said to be ornithophilous. Ornithophilous, meaning “bird-loving.” So we have ornithophilous plants and you might say we have ornithophilous humans, like you and me.

In the same patch of forest, dozens of hummingbird species can eat the same thing—flower nectar—while coexisting in relative harmony because they have evolved different bill lengths and shapes and they feed on different plant species.

It's fascinating to see the close correspondence in hummingbird bill shapes with the flowers they feed from. Some hummingbirds have short, straight bills and feed from flowers that have a shallow, straight tube shape. The 7 thornbill species are in this category. Other species, like the White-tipped Sicklebill, have a long, down-curved beak which allows them to feed from crescent-shaped flowers with nectar hidden deep inside.

Sword-billed Hummingbird in Ecuador.
Sword-billed Hummingbird in Ecuador. Photo by Ivan Phillipsen.

In the cloud forests of Ecuador, I was lucky enough to get a great look at the Sword-billed Hummingbird. This bird’s beak is longer than its body! It feeds from large flowers that have long corolla tubes—such as Datura, Fuchsia, and Solanum species. It’s such a crazy-looking, awesome bird.

Alright, now let’s talk about how all this hummingbird diversity is distributed in the present day.   

Diversity and Distribution

Of the approximately 250 bird families in the world, the hummingbird family ranks second in having the greatest number of species. Only the Tyrant Flycatcher family, Tyrannidae, contains more species.

There are 349 hummingbird species in the family Trochilidae. That’s according to the Clements Checklist of Birds of the World. So this family of tiny birds is mega-diverse. In evolutionary terms, the hummingbirds are a great success.

As I mentioned, all of these species are found in North, Central, and South America. One species, the Rufous Hummingbird, gets as far north as southeastern Alaska. The Green-backed Firecrown lives at the southern geographic extreme, getting all the way down to Tierra del Fuego in Argentina. 

Hummingbirds are found in nearly every habitat across their range, from deserts to jungles. They also span a broad range of elevations, from sea level to 17,000 feet, which is about 5,200 meters.

The diversity of hummingbirds is distributed unevenly across the group’s range. The highest concentration of hummingbird awesomeness is found in forests of the northern Andes in South America. Ecuador has about 140 species and Colombia has a whopping 170!

Why are there so many species in this region? Well, the Andes mountains have been rising in this area since the first hummingbirds arrived 22 million years ago. More topographic relief in this area has created geographic diversity in rainfall and temperature, which allowed for more plant diversity and thus paved the way for the existence of more habitat types. And since the evolution of hummingbirds is closely linked with that of their food plants, the birds split into more species in tandem with the plants. That’s the basic idea, anyway. That’s the hypothesis.

And as I alluded to earlier, many hummingbird species can evolve to live side-by-side through resource partitioning. Hummingbirds all need flower nectar, but different species can coexist in the same small area if they each get this limited resource in a different way and/or from different plant species. The northern Andes hotspot has a multitude of habitats and, because of resource partitioning, many hummingbird species can be packed into each of these habitats.  

So hummingbird diversity is centered in the neotropics, big time. But we have a handful of them here in the United States. About 20 species. That’s enough to keep us American bird-lovers at a baseline level of happiness, I suppose. With any fewer species, we might go into withdrawals and clinical depression.

Hummingbird Flight

What puts the “hum” in hummingbird is the sound of tiny wings beating against the air at high speed. A typical hummingbird beats its wings 80 times a second. Yes, that’s 80 times every second. Our human eyes can’t detect movements faster than 50 times a second, so we just see a blur in the space where hummingbird wings are flapping furiously.

These are the only birds that can hover for sustained periods of time. This ability allows them to maintain a perfectly stable head position in flight, as they dip their bills into flowers while feeding. They can keep their heads in the same position even when battered by gusts of wind.

And not only can hummingbirds hover, they can fly in any direction: straight up, down, side to side, and backwards. They can even fly upside down for short bursts. 

They accelerate like rockets and routinely reach speeds up to 35 mph or about 55 kph. When they dive, hummingbirds can even get up to speeds over 50 mph, which is about 80 kph.

Ruby-topaz Hummingbird on the island of Trinidad.
Ruby-topaz Hummingbird on the island of Trinidad.

With respect to maneuverability, hummingbirds are the avian equivalent of the remote-controlled camera drones that all the kids seem to have these days. The difference is, most of us are actually happy to see a hummingbird fly over our house.

The aerial prowess of these birds comes not only from being able to flap their wings so dang fast but also from the actual stroke they use for each wingbeat. Observed with slow motion video, we can see that hummingbirds move their wings in a horizontal figure-eight pattern. This gives the bird lift on both the downstroke, as in other birds, but also on the upstroke, which is remarkable. About 25% of a hummingbird’s lift comes from the upstroke.

Metabolism

The superpower of sustained hovering flight comes at a cost. To keep their little wings beating at such high rates, hummingbirds need to burn lots of fuel. They need to eat a lot and they must have high metabolisms to convert their food into kinetic energy.

It turns out that hummingbirds have the highest metabolisms of all animals, excluding some insects. During flight, their heart rate can be up to about 1,200 beats per minute! Meanwhile, they are taking 250 tiny, adorable breaths each minute.

This turbocharged metabolism is powered by the sugars found in flower nectar. This liquid comprises a combination of sucrose, glucose, and fructose. Other birds burn fat to power their flight, but hummingbirds use these sugars. They can quickly convert nearly 100% of the sugar they eat into energy for their flight muscles. Humans, at their best, can convert only about 30% of recently eaten sugar.  

To sustain their high metabolisms, hummingbirds must feed a lot. From dawn to dusk, they spend a lot of time seeking flowers to sip from. This is a crazy circular situation: to hover, a hummingbird must beat its wings fast; to beat its wings fast, it must have lots of energy; to have lots of energy, it must have a high metabolism; to have a high metabolism, it must consume lots of fuel; to find and consume lots of fuel, it must hover and beat its wings fast. 

So it’s just like the old saying: Eat to hum and hum to eat.

If you’re a bird, why not just eat something besides flower nectar and save yourself all this trouble? 

Because if you can specialize in eating flower nectar, you aren’t competing with other types of birds. You have a rich resource to yourself, more or less. You have your own niche and you can be the master of that niche. 

Okay, so you might have to chase off the occasional bumblebee or butterfly, but those guys are lightweights. You can take ‘em.

So what happens to hummingbirds at night, when they don’t eat for 6-10 hours? Well, what they do is slow their metabolisms way, way down. They turn the dial from 11 to 1. They sleep deeply, in a sort of hibernation called torpor. During their nightly torpor, their body temperatures drop by up to 40 degrees and their hearts beat at only 50-100 beats per minute. When dawn breaks, a hummingbird might have lost 10% of its weight overnight. That’s even when its metabolism had been slowed during torpor. Without this torpor ability, this adaptation, a hummingbird would likely starve to death overnight.

How do Hummingbirds Eat?

Different hummingbird species have different strategies for getting flower nectar. If the flowers they prefer tend to produce lots of nectar continually, then the birds stay close to a particular flower patch and defend it fiercely from other birds. This pugnacious behavior is common at your backyard hummingbird feeder, which I’m sure you’ve noticed. 

Another common foraging strategy is called traplining. This is where a hummingbird makes a regular circuit of several flower patches. The bird may make this circuit one time each day, or many times. This is more common for species that feed from flowers that have lower rates of nectar production. The name traplining comes from what fur trappers do: they routinely check a series of mammal traps laid out across the landscape.

When feeding, hummingbirds stick their thin bills into the tube of a flower and then use their tongues to suck up the nectar. Their tongues are super long, forked, and shaped like two parallel, hollow tubes. These tubes open up along the side to let in nectar, and then they close before pulling back into the mouth. This pump action happens very fast and is repeated rapidly.

Great Sapphirewing Hummingbird in Ecuador.
Great Sapphirewing Hummingbird in Ecuador.

Hummingbirds aren’t always flying around looking for their next meal. They spend a fair amount of their day perched. They groom their feathers, rest, and watch out for competitors to chase off. During the breeding season, males try to win over females while females have the task of raising young.

Now I’ve been saying nectar this and nectar that, as though the only thing hummingbirds ever eat is flower nectar. But if that were the case, these birds could not get the protein, vitamins, and minerals that they need to survive.

Insects and other small invertebrates like spiders are very much on the menu for hummingbirds. These bugs provide the nutrients that nectar doesn’t have. Hummingbirds eat spiders, caterpillars, and insect eggs by gleaning them from flowers, branches, and leaves. 

Or they catch bugs in mid-air. In a behavior called hawking, a hummingbird will perch on a twig and scan the sky for small, flying insects. Then it will dart out to chase its quarry. Sometimes the bird just hovers in a swarm of insects and zips back and forth, gorging like a dolphin in a school of fish.

Remember that swifts and hummingbirds are closely related. Swifts are masters of catching insects on the wing. Hummingbirds, too, are adept at nabbing tiny bugs while flying.

You’d think hummingbirds would do this by using their beaks like tweezers. But researchers have found that what they do is catch flying insects using the base of their bill, not the tip. Perhaps not coincidentally, this is similar to how swifts catch their prey.

We’ve been talking about what hummingbirds eat. But you might wonder, “What eats hummingbirds? Who are their predators?”

In a natural setting, there don’t seem to be predators that specialize in eating hummingbirds. Some larger birds like hawks will sometimes snatch a hummingbird. But a hummingbird is hardly more than a mouthful of meat for most predators of this size. And they’re probably not very easy to catch, given their ability to zoom away at high speed in any direction.

However, there are many reports of what seems to be opportunistic predation on hummingbirds. The most common examples are of enormous spiders and praying mantises capturing and eating hummingbirds. I know spiders gotta eat, and you can’t blame them, but yikes, this is just kind of macabre to think about. So it goes...

The most widespread and effective predator of hummingbirds is the house cat. Domestic and feral cats are devastating to small birds, and hummingbirds are no exception. This is worse than spiders, in my opinion, because it’s not natural and it’s totally preventable. I won’t get started on the problem of cats versus wild birds… I’ll save that for another blog post. But please, think twice about letting your cat outside, where it can kill hummingbirds. Because I know you don’t want that to happen.

Breeding

During the breeding season, hummingbirds set up territories, which they defend from their rivals.

A male hummingbird establishes a territory that includes some nectar-producing flowers. The size of a territory varies from species to species and with nectar availability. Some are hundreds of square yards or meters, while others cover thousands of square yards.

To keep any pesky rival males out of his territory, the resident male will first try to scare them off with warning vocalizations. He’ll usually flash his brilliantly colored head feathers at the same time. If this doesn’t work, our male gets physical. He chases the interloper and maybe even attacks with beak and claws to get rid of him.

The male is hoping that females will enter his territory to feed from his flowers and that they’ll take notice of him and mate with him. 

To get noticed, the male hummingbird performs a display. Many species have what is called a shuttle display, where the male does an aerial dance right in front of the perched female. While he hovers and shimmies side to side, he spreads his tail feathers and shows off his brightest, most colorful head and body plumage to the female.

Some species, particularly in North America, have another trick up their tiny sleeves: the dive display. This is where the male, after zeroing in on a particular female, tries to impress her by flying high over her perch, then diving toward her at high speed in a J or U-shaped flight path. At the bottom of his dive, the male often flares his shiny feathers and also makes a loud sound.

The cool thing about this sound is that it’s produced not by the male bird’s voice, but by his feathers. Feather sonation, as it’s called, is when air moving fast over a feather makes a sound. The trilling or buzzing sound of a diving male is distinct for each species that shows this behavior.

These dive displays are amazing. If you adjust for body size, a diving male hummingbird achieves the highest velocity of any vertebrate animal. His speed can be up to 385 body lengths per second. If a six-foot-tall human were to move that fast, they would be going 1,500 mph, which is 2,400 kph. Insane. These birds are experiencing up to nine times the force of gravity, a magnitude that only jet fighter pilots might relate to.

Assuming all this frantic displaying wins the affection of a female, the male will mate with her and then the two birds will go their separate ways. The male plays no role in raising his young. He will mate with multiple females in his territory, if possible. And if females don’t show up, or they stop showing up, he will pack up and leave, to find a new territory.

Females also establish territories, but not for the purpose of mating. Females defend areas that offer great nesting habitat. A female’s territory may have flowers, but it isn’t necessarily close to a male’s territory. 

A female will often vigorously attack other female hummingbirds that trespass on her territory. She’ll also harass any would-be predators of her eggs or nestlings: jays and other birds, snakes, or mammals like squirrels.

Hummingbird nests are tiny, cup-shaped structures. They’re typically smaller than a ping pong ball. Plant material in the nest is held together and the whole structure is attached to a branch with the help of spider silk, which is incredibly strong for its weight. The nest is often decorated on the outside with pieces of lichen, which helps to camouflage it.

You won’t be surprised to hear that hummingbirds lay the smallest eggs of any bird. Each egg is about the size of a small bean and is so small that it could probably fit in your belly button.

Females normally lay only one or two eggs. The chicks are fed a diet of small invertebrates, to supply them with plenty of protein, and mom gives them a healthy supply of flower nectar too. Young birds are ready to leave the nest in about three weeks.

Female Annas Hummingbird with two chicks.
Female Anna's Hummingbird with two chicks. Vancouver, British Columbia, Canada.

Hummingbird Migration

Some hummingbirds migrate long distances. This is especially true of many North American birds that enjoy abundant flowers in the spring and summer in the US and Canada, but would face starvation and freezing to death in the winter if they stayed in these northern latitudes. These species must head to warmer places in the winter.

Young hummingbirds migrate for the first time on their own, with no guidance from mom. For their first journey south, their orientation is purely instinctual, it’s hard-wired into their miniscule brains by their genes. If they survive that first migration, they will remember landmarks and celestial cues to find their way the next time.

In one amazing example, some individual Ruby-throated Hummingbirds fly straight across the Gulf of Mexico, nonstop for hundreds of miles as they fly south for the winter from the eastern US to Mexico. This is an incredible feat for such a small bird. They can’t stop to refuel or rest on this journey. They get the energy they need by burning fat reserves.

Similarly impressive is the epic migration of the Rufous Hummingbird. If you adjust for body length, this species makes the longest round-trip migration of any other bird. Some individual Rufous Hummingbirds go as far north as Alaska, as I mentioned earlier. No other hummingbird species gets so far north. These same birds fly all the way to Mexico in Winter. 

Studies of banded hummingbirds have often revealed extreme fidelity to particular locations. These birds can remember where there were flowers or feeders in previous years, and they will sometimes return to the exact place on the same day from one year to the next. If you take down your hummingbird feeder, don’t be surprised next spring if you have hummingbirds hovering around the spot where the feeder used to hang. They will guilt trip you into putting your feeder back up.

Banding studies have also revealed that hummingbirds can be surprisingly long-lived for such small animals. Some individuals have lived over 10 years. The average is more like 3 to 5 years.

Feathers

No discussion of hummingbirds is complete without talking about their amazing feather colors. It isn’t an exaggeration to describe these birds as jewel-like. From some of their names (for example, the Ruby-topaz Hummingbird in the photo above) it seems many scientists agree that hummingbirds look like living gemstones.

Violet-tailed Sylph in Ecuador.
Violet-tailed Sylph in Ecuador. Photo by Ivan Phillipsen.

A key feature of hummingbird plumage is the prevalence of iridescent colors. These are the metallic-looking colors that are most well-developed on the heads and upper bodies of males. These colors shift their hue depending on the angle we view them from. For example, from the side the feathers on a male hummingbird’s head might look almost black. But when seen head on, in full sunlight, the feathers take on a luminous purple sheen.

Buff-winged Starfrontlet in Ecuador.
Buff-winged Starfrontlet in Ecuador. Photo by Ivan Phillipsen.

Iridescence is not unique to hummingbirds, since many other types of birds show some level of this sort of coloring. Hummingbirds have just taken it to an extreme. They dazzle each other, and us, with their scintillating greens, oranges, blues, and other iridescent colors.

Males sport these amazing colors to impress females and to signal to their rivals they mean business.

One special term we use for the iridescent feathers on the throat of a hummingbird is gorget (pronounced “GOR-jit”). This word comes from the name of the metal collar worn by an armored knight. Medieval knights wore gorgets around their necks.

Feeding Hummingbirds in Your Backyard

It’s a wonderful thing to see these tiny birds up close, right out the kitchen window. Countless people have hummingbird feeders hanging up, and it's great that there’s so much interest.

But is it okay to feed these birds? This is a good question to ask. Sure, the hummingbirds are happy to have the free food, but do they know what’s best for themselves? Maybe not. 

So are there any downsides to supplementing their diets with artificial feeders? Well, it depends on who you ask, but it seems that the consensus is that feeding hummingbirds is not harmful to the birds.

Not that there are no wider consequences of feeding. Because there are. And there is a caveat: feeding isn’t harmful to the birds IF done correctly. I’ll get to that in a moment.

But what are the wider consequences? Some research shows that, given the choice, hummingbirds spend more time at artificial feeders than among the native plants they normally feed from and pollinate. It’s conceivable that this could negatively affect the reproduction of those plants.

Another consequence is that feeding hummingbirds might concentrate individuals unnaturally, which could have consequences for their local population, either good or bad.

There is also evidence that feeding has allowed some species to expand their ranges. For example, Anna’s Hummingbird used to be confined mostly to the state of California in the US. But this species has expanded far to the north in recent decades, in step with the increase in non-native, cultivated flowering plants in cities and towns, and the year-round availability of artificial feeders. Is this “bad” for the Anna's Hummingbird? Probably not. But it is affecting their biology.

Male Rufous Hummingbird at an artificial feeder.
Male Rufous Hummingbird at an artificial feeder.

Some suggest that artificial feeders will cause migrating hummingbirds to hang around too long in the autumn, so they are at risk of heading south too late for their own good. As I understand, this doesn’t appear to be what happens. Hummingbird species that migrate have deeply ingrained instincts driving their behavior. These instincts tell them when is the best, safest time to leave and where to go. 

More research may someday reveal that there are other complications with feeding hummingbirds. But so far, it seems to be an okay thing to do.

So if we’re going to feed hummingbirds, let’s do it right!

Here are a few tips:

First off, the recipe for the perfect hummingbird food is 1 part white table sugar (i.e. sucrose) to 4 parts clean water. For example, put a quarter cup of sugar in a measuring cup, add 1 cup of boiling water. Stir until the sugar dissolves, then let the solution cool to room temperature. Viola!

Don’t use food coloring and don’t use any commercially produced, so-called hummingbird food.

Don’t use artificial sweeteners like aspartame. Hummingbirds, with their finely tuned ability to detect sweetness, will ignore pure water or solutions with less than 10% sugar. But aspartame will fool them and it has no calories, so it’s useless. You and I might need to lose a few pounds, but your hummingbirds get plenty of exercise just living their little lives. They need the calories.

You also want to avoid honey or anything besides good ol’ white sugar. Just use the recipe I gave you.

It’s very important to keep your feeder clean. Hummingbirds can get fungal infections from dirty feeders. Wash your feeder out at least once a week with hot tap water and perhaps a weak vinegar solution. Don’t use bleach.

You also want to hang your feeder high enough that it’s safe from any lurking house cats. Likewise, keep your feeder at least 10 feet from any bushes where a predator could hide.

And my last tip for feeding hummingbirds? Try planting some native flowers in your yard. This is a great way to invite not only more hummingbirds into your life, but it also beneficial insects and other wildlife. It’s a win-win situation. 

I’ve got a small hummingbird feeder at my house, but I’m adding more and more native plants to the yard, and I just love creating these patches of natural habitat. I also plan to create a pollinator garden, filled with native flowering plants. That will be great for bringing in the butterflies, bees, and of course, hummingbirds.

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