Hummingbirds are known for their vibrant, iridescent plumage that shimmers in the sunlight. The colours and patterns of a hummingbird’s feathers play an important role in courtship displays and camouflage. While male and female hummingbirds share some similarities in colouration, females tend to be less brightly coloured than males. The reasons behind this colour difference have to do with evolution, reproduction, and habitat adaptation.
Plumage Differences Between Males and Females
In most hummingbird species, the males have brightly coloured, iridescent feathers in hues of red, orange, green, blue and purple on their throats, heads, tails or wings. This bright plumage is thought to have evolved through sexual selection, whereby females prefer males with the brightest, most vibrant feathers during courtship. The brighter the male, the healthier he appears, and the more attractive he is to potential mates.
Female hummingbirds, on the other hand, tend to have duller, less conspicuous plumage in shades of green, brown and grey. Their subdued colours help them to blend in with their surroundings while incubating eggs and caring for young. Drab plumage provides camouflage from predators. Females also lack the colourful throat patches and elongated tail feathers that males use in courtship displays.
Evolutionary Reasons for Differences
The differences in male and female hummingbird colouration likely stem from their contrasting reproductive roles. Males take little part in raising young, so their feathers can afford to be flashier to attract mates. Females invest more energy in incubating eggs and rearing chicks, so they benefit from camouflage. Thus, natural and sexual selective pressures drove the evolution of dimorphism between the sexes.
In most hummingbird species, females select their mates based on these elaborate male displays. Since brighter males tend to be fitter, mating with them ensures healthier offspring. Male colours also signal dominance and the ability to defend high-quality breeding territories. Furthermore, male plumage indicates genotype – a genetically superior male can produce more colourful feathers.
Exceptions and Unique Species
While sexual dimorphism is the norm, some exceptions exist. For example, female bee hummingbirds have a reddish throat patch like males. In woodstars, both sexes have colourful plumage. In some species, females have a slightly duller version of the male’s ornamentation.
| Species | Female Colouration |
|---|---|
| Anna’s Hummingbird | Green and grey overall, with rose-pink throat |
| Ruby-throated Hummingbird | Green above, white below with faint red throat |
| Rufous Hummingbird | Green, brown, rusty orange and white |
| Calliope Hummingbird | Bronzy green above, pale grey throat with purple dots |
In species where males and females look alike, it suggests factors other than sexual selection played a role in feather evolution. For instance, similar drab plumage in both sexes may be an adaptation for life in overcast, humid cloud forests.
Geographic Variation
The colours and patterns of female hummingbirds can vary across different geographic regions and habitats. For example, northern populations may be duller than tropical ones if brighter feathers carry energy costs. Higher ultraviolet light exposure near the equator can also intensify colours.
Likewise, females may match the colours of local flowers. Costa’s Hummingbirds along the Pacific Coast have more purple-red plumage to blend with monkeyflower, a key nectar source. Altitude affects colour too – higher elevation females may have darker back feathers for heat absorption.
Iridescence
While female hummingbirds lack the shocking brilliance of males, many do possess iridescent plumage. Iridescence is caused by microscopic structures in the feathers that refract light. The structures are melanosomes – organelles full of the pigment melanin. Melanosome shape, density and distribution determine the feather’s colour.
Oval melanosomes produce red or orange, while elongated ones make green or blue. Females may have fewer overall melanosomes compared to males. By interacting with air pockets in the keratin feather structure, the melanosomes split white light into pure spectral colours through interference effects.
As light hits the feather barbules from different angles, different wavelengths are reflected, creating a shimmery glow. The fuel required to produce elaborate melanosomes may explain why males have more vibrant iridescence – they can spare more energy for plumage quality.
Coloured Feathers Serve Multiple Functions
While female hummingbirds are more cryptically coloured than showy males, their plumage is often still brightly patterned. Iridescence, streaks, dots and colour mixing help break up their outline so they blend into foliage. This provides camouflage from predators when incubating.
Female-specific colours may also signal readiness for breeding. Some species develop colourful spotting during the fertile period. This helps attract males at optimal times for successful mating. Once the breeding season ends, moulting obscures the ornamentation.
Additionally, in species where both sexes feed on nectar, some colouration similarity improves dominance over flowers. Intimidating rivals ensures sufficient food access. Colour also absorbs more heat from the sun to help maintain a high metabolism.
Conclusion
While female hummingbirds tend to be less gaudily coloured than males due to differences in reproductive strategy, they utilize colour in subtle yet complex ways. Their understated plumage patterns serve purposes of camouflage, heat absorption, breeding displays and competition. Iridescence provides some dazzle using microscopic feather structures. So, while a female’s colours are more muted, she is just as vibrantly decorated as needs dictate.
