Hummingbirds are some of the smallest birds in the world, captivating people with their speedy flight and ability to hover in midair as they drink nectar. Their tiny size leads many to wonder – between male and female hummingbirds, which sex is smaller on average?
The answer is that for most hummingbird species, the male is the smaller sex. This is due to a phenomenon called sexual size dimorphism, where the two sexes of the same species exhibit differences in body size or appearance. For hummingbirds, males are usually around 5-10% smaller than females on average.
There are a few key reasons why male hummingbirds are tinier than their female counterparts:
Higher Costs of Reproduction for Females
Producing and laying eggs represents a significant energy investment for female hummingbirds. The female needs additional body reserves to develop eggs and maintain her health throughout breeding. The extra energy demands favor a larger body size.
Male hummingbirds do not carry these reproductive costs, so they can get away with being more petite. Their small size enables males to be extremely agile and maneuverable in flight during courtship displays.
Competition Between Males
Male hummingbirds are highly territorial and competitive when it comes to attracting females. They perform elaborate courtship rituals, flying in loops and dives to show off for potential mates.
The smaller male body is better adapted for these energetic mating displays in midair. Greater agility and acceleration help males outcompete others when engaging in fights or chasing females.
Advantages of a Smaller Size
In addition to courtship, a tiny male body size has other advantages that promote survival. Being lightweight allows hummingbirds to conserve energy in flight and hover longer while feeding on nectar.
Smaller males are also more nimble when evading predators or establishing prime feeding territories. Their high metabolism and rapid wingbeats are energetically expensive, so a compact body minimizes energy needs.
Size Differences Across Hummingbird Species
While male hummingbirds are uniformly smaller than females, the degree of sexual size dimorphism varies significantly depending on the species.
Some examples:
Ruby-throated Hummingbird
The ruby-throated hummingbird shows only slight sexual size dimorphism.
– Females average 9 cm long and weigh around 3 grams
– Males average 8 cm long and weigh 2.4 grams
For this species, males are only about 13% smaller than females – a relatively modest difference. Both sexes have similar slender silhouettes.
Rufous Hummingbird
In the rufous hummingbird, the size divergence between the sexes is more pronounced.
– Females have an average length around 8.5 cm and weigh 3.4 grams
– Males measure only 7 cm on average and weigh 2.2 grams
So for this species, males are about 18% smaller than the females.
Calliope Hummingbird
The Calliope hummingbird displays the most extreme sexual size dimorphism of any North American hummingbird.
– Females measure up to 9 cm long and may weigh more than 4 grams
– Males are only about 5 cm long and weigh around 2 grams
Here, males are nearly half the length and weight of females! This puts them among the smallest birds in the world. The Calliope’s diminutive males must work especially hard to hold their own when mating.
Key Differences in Appearance
In addition to their petite size, male hummingbirds can be distinguished from females by a few key physical differences:
Brightly Colored Throat Feathers
Males of most hummingbird species have brightly colored, iridescent feathers on their throat. Depending on the species, these can be ruby red, vivid orange, electric blue, or emerald green.
Females lack these flashy throat patches. Their throat and chest feathers are relatively drab with muted grays, greens, or whitish colors.
The vibrant male throat feathers (called a gorget) play an important role in attracting mates. When excited, the male can orient these iridescent feathers towards a female to catch the light.
Tail Shape
Male hummingbirds tend to have differently shaped tail feathers compared to females:
– Males have more forked, V-shaped tails
– Females have rounded or squared-off tails
This also aids males during courtship displays, allowing them to show off their tail feathers in dramatic fanning motions.
Bill Size
While the difference is subtle, males tend to have longer, more slender bills than females. This matches their smaller body size.
Females often have slightly shorter, sturdier bills. Their bill shape is likely adapted for battles over food resources and nest materials.
Do Females Ever Look Like Males?
For most hummingbird species, the physical differences between males and females are distinct and consistent across individuals. However, in a few types of hummingbirds, some females take on a nearly male-like appearance. For example:
Black-chinned Hummingbird
In the black-chinned hummingbird, females may occasionally display some iridescent throat feathers like a male. However, their colorful gorget is smaller and less vibrant than a typical male’s. Their other features like size and tail shape still resemble a standard female.
Anna’s Hummingbird
Up to 1% of female Anna’s hummingbirds exhibit male-like traits. These rare females have a reddish gorget, forked tail, and whistle-like song. They may also behave more territorial, like males. However, they still retain a female-sized body.
Costa’s Hummingbird
Female Costa’s hummingbirds sometimes develop an orange throat patch that resembles males. These “ornamented” females make up about 15-20% of the female population. They use their male-like features in courtship displays to attract other females for mating.
Comparison of Body Size Measurements
This table summarizes the average body size dimensions of male and female hummingbirds for some of the most widespread species:
| Species | Sex | Total Length (cm) | Wingspan (cm) | Weight (g) |
|---|---|---|---|---|
| Ruby-throated | Female | 9 | 11.5 | 3.0 |
| Ruby-throated | Male | 8 | 10.5 | 2.4 |
| Black-chinned | Female | 9.5 | 12 | 3.5 |
| Black-chinned | Male | 8.5 | 11 | 2.7 |
| Anna’s | Female | 11.5 | 13 | 4.5 |
| Anna’s | Male | 9.5 | 12 | 3.4 |
| Calliope | Female | 9 | 11 | 4.1 |
| Calliope | Male | 5 | 7 | 2.0 |
The table highlights that even closely related species can vary substantially in size dimorphism between the sexes. For instance, the difference is modest for ruby-throats but extreme for calliopes.
Differences in Behavior and Roles
Beyond physical dissimilarities, male and female hummingbirds also play distinct roles in terms of behavior:
Feeding
Male and female hummingbirds have essentially identical diets, feeding on flower nectar, tree sap, and small insects. However, they may exhibit slightly different feeding strategies:
– Males tend to prefer higher sugar concentrations in nectar and dominate rich food sources.
– Females are more generalized in their feeding and visit a wider variety of flowers.
Territory Defense
Males are much more aggressive and territorial than females. They stake out nesting areas in the spring and chase away intruders.
Females may skirmish over resources, but do not actively defend large territories. They mainly focus on breeding and caring for young.
Migration
In species where the sexes migrate separately, males usually migrate north first to secure prime nesting spots early. Females follow a week or two later.
Some male hummingbirds skip migration altogether and overwinter farther north if food is abundant. Females migrate more consistently due to higher energy demands.
Nesting
Females alone build the nest out of soft plant down, spider webs, and lichens. They incubate the eggs and care for the hatchlings.
Males may contribute some nest materials, but otherwise have little parenting involvement beyond mating.
Vocalizations
Male hummingbirds produce complex, melodic sounds with their syrinx vocal organ during courtship displays. Females vocalize much more simply, using short chips or squeaks.
Why Small Size Evolved in Males
Scientists propose two major evolutionary drivers that led to the small size of male hummingbirds over time:
Sexual Selection
Extreme elaboration of male sexual traits is common in birds where females have sole parenting responsibility. Hummingbird mating displays place intense pressure on males to be as agile and maneuverable as possible. Smaller bodies with long tails and wings provide an advantage.
Competition for Nectar
Hummingbirds exist at surprisingly high densities, creating intense resource competition. Smaller males are better able to survive on limited nectar availability. They can also dominate in aerial battles over the best flower patches.
In combination, these factors of female choice and feeding competition have shaped males into incredibly tiny, high-performance flying machines over the course of hummingbird evolution.
Conclusion
While hummingbirds rank among the most diminutive birds worldwide, males achieve an even more miniature stature than females in most species. This distinct size dimorphism arises from differences in reproductive costs, mating strategies, and resource competition between the sexes.
Careful inspection reveals clear physical differences as well, with males possessing vibrant gorgets, forked tails, and slightly longer bills. So next time you manage a fleeting glimpse of a hummingbird, take a closer look – the male is likely the smaller, flashier one! By understanding what makes each sex unique, we gain greater appreciation of hummingbird diversity and behavior.
