Sometimes nature surprises us with extraordinary products of evolution. One prime example is the extraordinary sword-billed hummingbird (Ensifera ensifera). These relatively small birds have carved a niche in the animal kingdom with their extraordinary morphology. They boast one of the world’s longest bills, setting them apart in a world of aerial acrobats.
Surprisingly, despite the namesake ‘swords,’ these hummingbirds do not employ their bills for combat. Unveiling the true purpose of these elongated beaks reveals a twist in their evolutionary tale, adding an ironic layer to their remarkable adaptation.
What’s so cool about Sword-billed hummingbirds?
Measuring between 13 and 15 centimeters (5.1–5.9 inches) in length, sword-billed hummingbirds stand out as some of the largest hummingbirds in the world. What makes them particularly intriguing is that this measurement doesn’t even consider their remarkably long beaks.
The average length of a sword-billed hummingbird’s beak ranges from 8 to 12 centimeters (3.1–4.7 inches). Their beaks are approximately two centimeters longer than the body of the world’s smallest bird—the Bee Hummingbird (Mellisuga helenae).
Similar to many other species of hummingbirds, swordbills are South American natives. Prevalent along the northwestern coasts, these birds can commonly be found in six countries across the continent. Their distribution closely mirrors the natural path of the Andes and extends from the northern tip of the continent, in Venezuela, to the forests and scrublands of Bolivia.
The insane morphology of sword-bills
Many birds have ridiculously long beaks, including sword-bills. However, sword-billed hummingbirds have something in particular that sets them apart. For certain individuals, their beaks are actually longer than the entire length of their bodies! These birds boast the largest beaks in the world relative to their body size.
Spotting sword-bills in the wild
If the ridiculously long bills aren’t enough of a distinction; there are a few other features that set sword-billed hummingbirds apart. These birds are sexually dimorphic, meaning the males and females of the species do not look alike and can be distinguished from one another.
Sticking to the theme, male sword-bills are more vibrant than females. They catch your attention with their iridescent plumage and depending on the day, exhibit shades of green, blue, or violet. Depending on the angle of sight, the gorget shines different hues of vibrant color to the observer. Similar to many other species of hummingbirds, these boys sport brownish-copper-colored heads as well as an iridescent gorget — the colorful patch on their throat.
Females, on the other hand, exhibit a drab coloration and have more subdued colors, often featuring more greens and browns. Additionally, females generally do not have a vibrant gorget. If they do have one, it is generally less vivid than that of males.
Behavior-wise as well, males and females differ a bit. Although both sexes are prone to territorial displays, the females do not engage in flashy shows of courtship that males do.
Can sword-bills fly?
Surprisingly enough, the bill doesn’t impede the hummingbird’s abilities in flight. Not only can these birds effectively fly; they can hover, fly forward, backward, and even upside down. However, there are a few things that sword-bills can’t do. For instance, most birds preen — groom themselves — at their bodies with their beaks. However, given the size of the sword-bills’ beaks, these birds need to use their feet instead to peck at themselves.
Why such a long beak?
Contrary to what their name might suggest, these tiny birds don’t employ their elongated bills as tools for combat. In reality, sword-bills are a bit more docile. Unlike many hummingbird species, such as the Rufous hummingbird, sword-bills aren’t prone to aggressive behavior and rarely engage in fights with individuals of other species. Though territorial, these birds have a unique approach to ensuring they harvest nectar from flowers. Instead of using their “swords” to fight, they use them for feeding!
In the world of hummingbirds, nectar is gold. This carbohydrate-rich liquid constitutes a substantial portion of any hummingbird’s diet. Not only is this resource energy-rich, a crucial aspect for metabolically demanding birds like hummingbirds, but it is also limited.
Within any flower patch, there is a finite number of flowers containing a limited amount of nectar. This scarcity leads to intense resource guarding among hummingbirds. Species like the Anna’s hummingbird and the Rufous hummingbird are notorious for fiercely defending their nectar patches from both conspecifics as well as individuals from other species.
The evolutionary history of sword-billed hummingbirds is fascinating. These birds didn’t just evolve in isolation. They co-evolved with flora; specifically flowers like the passionflower. Unlike species like the ruby-throated hummingbird, sword-bills do not migrate. In stark contrast to their North American counterparts, indigenous South American species — like the sword-billed hummingbird — are mostly sedentary and choose to establish year-round residency in their warm habitats. The lack of migration in these hummingbirds means they need to find reliable food sources year-round in their resident habitats.
Of birds and flowers
Hummingbirds typically compete for nectar from the flowers they like, such as dahlias, fuchsias, and verbenas. Sword-billed hummingbirds, on the other hand, face much less competition for resources. Using their ridiculously long bills, these birds have evolved to almost exclusively collect nectar from atypical — hard to reach — flowers. Such atypical flowers, like the passionflower, generally have elongated floral tubes that store nectar.
These birds need a lot of energy to get through the day; they require some form of food almost every 10 minutes! They need to consume a remarkable 50 percent of their body weight daily.
Co-evolution: sword-billed hummingbirds and passionflowers
For a majority of hummingbirds, interacting with flowers like the passionflower is a futile endeavor. However, for the sword-bills, the passionflower is anything but. Thanks to their elongated bills, these birds effortlessly navigate the tubular structures of the flower, skillfully extracting all that golden liquid for themselves.
It’s not just a stroke of luck; this is the result of millennia of co-evolution with passionflowers. The extent of this co-evolution between the two is so profound that sword-bills almost exclusively feed on passionflowers, and reciprocally, passionflowers are nearly exclusively pollinated by sword-bills. The degree of interdependence is so ingrained that the geographical ranges of both species exhibit an uncanny level of overlap.
Passiflora, commonly known as passionflowers, encompasses a diverse genus within the family Passifloraceae. With over 550 individual species, the genus is a large one, with a cosmopolitan distribution. For instance, while most species thrive in South America, they also have a global presence, extending to regions like North America and Asia. Within South America, Colombia, in particular, stands out as a hotspot for passionflower diversity, boasting over 167 documented species. Other countries, such as Bolivia, Brazil, Ecuador, Peru, and Venezuela, all house a healthy diversity of passionflowers.
Recent research
Co-evolution isn’t uncommon in the wild. Charles Darwin first wrote about it when he was intrigued by the strange morphology of a Star-of-Bethlehem orchid (Angraecum sesquipedale). Upon observing the flower, he hypothesized to a friend, that only an animal equipped with an equally elongated proboscis could access the nectar hidden within the long spur. Conversely, only such a strange animal could pollinate the orchid as well.
Little did Darwin know at the time how true he was. About twenty years later, scientists would describe Darwin’s hawk moth (Xanthopan morgani): a moth with a nearly a foot-long proboscis that pollinates the Star-of-Bethlehem orchid.
The co-evolution between sword-bills and passionflowers is staggering. Over a hundred species of flowers are largely dependent on just one species of bird for pollination!
Think about it, while other hummingbirds — like the Annas and Rufouses — fight over nectar; sword-bills have free reign over hundreds of species of passionflowers within their range. Essentially, one tiny bird has effectively monopolized a very large clade of plants. This phenomenon is known as asymmetric co-evolution.
A game of (evolutionary) chess
In 2014, researchers conducted a DNA analysis using leaf tissues from 53 herbarium specimens, focusing on 43 species of Tacsonia—a supersection within the Passiflora genus. The study aimed to trace the origins of co-evolutionary interactions between sword-billed hummingbirds and passionflowers.
The scientists identified the crucial period of co-evolution — the first instance of interaction between the birds and the flowers — and were able to date it to approximately 11 million years ago. This timeframe also corresponds to the last known divergence of sword-billed hummingbirds from their short-billed hummingbird ancestor, the great sapphirewing (Pterophanes cyanopterus).
Additionally, the researchers were also able to pinpoint that around 10.7 million years ago, Tacsonia passionflowers diverged from the broader Passiflora genus. This divergence marked the point in time when the flowers acquired their distinctive long nectar spurs, a key characteristic that enabled the co-evolutionary relationship with sword-bills.
The study’s most captivating finding was that, when the population of sword-billed hummingbirds declined, passionflowers reverted and re-acquired normal-sized nectar spurs. Passionflowers were able to compensate for the loss of specialist pollination by reverting to a generalist morphology. Basically, when sword-bills were scarce, passionflowers reconfigured to accommodate short-billed species of birds!
One of the researchers, Susanne Renner, commented on the flexibility of Tacsonia flowers in a press release.
“That is why it is sometimes advantageous to break the highly specialized relationship with a single pollinator – and the group of long-tubed passion flowers we have studied includes good examples of such evolutionary switches,” opined Renner, in a press release.
Conclusion
Contrary to popular belief, these birds aren’t rare. According to the IUCN Red List, these birds are classified as a Least Concerned (LC) species. Although there currently exists no known abundance or density estimates for mature individuals of the species, the population is reported to be stable.
The birds are known to subsist in a range of habitats — from montane forests high-altitude tropical and sub-tropical shrublands and grassland — and is not known to be fragmented in its distribution. Additionally, like most hummingbirds, the species fares well in artificial habitats, like gardens and can be spotted feeding from hummingbird feeders.
