Horned larks are small songbirds found across North America. The males are distinguished by the black feathers that stick up like miniature horns on the top of their heads. These “horns” have puzzled scientists and bird enthusiasts for years. Why would a little brown bird need horns? Read on to learn the theories behind the horned lark’s unique head feathers.
What are horned larks?
Horned larks (Eremophila alpestris) are a species of lark found across North America. They are common in open spaces like fields, agricultural lands, and deserts. Horned larks get their name from the striking black feathers on the top of the males’ heads that resemble tiny horns. The females lack these distinctive feathers.
These songbirds reach 5-7 inches in length and have brown upperparts and white underparts. They have a yellow face and throat. Horned larks are mostly brown overall, helping them blend into dusty, dry landscapes. The horns really stand out against their muted plumage.
There are over 30 subspecies of horned lark across their vast range. Some regional varieties have paler or darker plumage or larger horns. For example, the pale-colored coastal horned lark of the Pacific Coast has almost white underparts. And the Sierra horned lark of California and Nevada has larger and darker head plumes.
Where did the “horns” come from?
The mini horns or head tufts of the male horned larks are actually modified feathers called plumicorns. Plumicorns likely evolved for display and are found on only a few types of birds. The horns begin growing after the larks’ incomplete first molt.
Interestingly, both male and female horned lark hatchlings initially have tufts of downy black feathers on their heads. These tufts disappear in the females as they mature, while they turn into display feathers in the males after their first molt.
Why do they have horns?
Scientists aren’t entirely sure why male horned larks sport tiny horns while females don’t, but they have some theories. Here are some of the proposed explanations:
For mate attraction
A leading theory is that the horns are for mate attraction and breeding displays. The striking black feathers help the males stand out and catch the eyes of females. Females likely evolved to lose the horns since they don’t need them to attract mates.
The horns are usually on full display during the mating rituals. Males will sing and fly high up in the air before diving back down with their head plumes and wings spread wide. The horns help make this aerial display more eye-catching.
For signaling dominance
The male larks may also use their horns to signal their dominance and fitness to other males. Larger and darker horns likely indicate better health and virility. Males will often face off with their head plumes flared and horns showing to intimidate rivals without physical contact.
For species recognition
Another proposed role is using the horns for easy species recognition, especially during flight. The distinct black head tufts allow the larks to recognize their own kind from a distance since they have otherwise drab, similar plumage.
Do the horns serve other purposes?
In addition to display and signaling, the horns may serve other functions:
Camouflage
When the larks press their horns down, the black feathers may help camouflage their heads against dark soil and shadows. This could provide some protection from predators when the birds are feeding on the ground.
Shading the eyes
Having horns may provide a bit of shade for the larks’ eyes when they are staring up at the sky scanning for predators like hawks. Although the horns are pretty small for significant shading.
Cushioning blows
One idea is that the horns help cushion blows to the head if the birds crash into vegetation when rapidly diving to the ground. However, the feathers are too small and flimsy to provide much real protective padding.
Theory | Evidence For | Evidence Against |
---|---|---|
Mate Attraction | Displayed during courtship, helps males stand out | Horns remain after mating season |
Dominance Signal | Larger horns indicate fitness, used in competitions | Rivals can assess fitness in other ways like flight displays |
Species Recognition | Distinctive identifying marker, aids recognition during flight | Other features like song also identify species |
Camouflage | Black feathers match dark soil | Horns small for significant camouflage effect |
Shading Eyes | Horns positioned over eyes | Horns very small, minimal shading effect |
Cushioning Blows | In position to potentially cushion head | Feathers too flimsy to cushion effectively |
Why don’t female horned larks have horns?
The horns serve little purpose for female horned larks. They do not need horns to attract males or establish dominance. If anything, the black feathers might make them more visible to predators.
One theory is that the gene for growing horns is carried on the male sex (Z) chromosome in horned larks. So it is only expressed in males, while females do not grow ornamental horns since they lack that chromosome.
Additionally, the horns have a high metabolic cost to grow and maintain. Since they provide no advantage to females, natural selection led to the loss of head plumes in mature females over time.
Advantages for males
- Attract mates
- Signal dominance
- Recognize species
- Possible camouflage and eye protection
Disadvantages for females
- Metabolic cost to grow feathers
- Increase visibility to predators
- No need for mate attraction or dominance displays
Do the horns affect horned lark behavior?
The presence of horns in male horned larks does seem to influence aspects of their behavior compared to females:
Song
Male horned larks have more complex and melodious songs than females. Their horns allow them to better showcase their vocal skills.
Aggression
Males tend to be more aggressive than females and actively defend their nesting territories. The horns signal fighting ability.
Predator mobbing
Males are also more likely than females to mob potential predators that enter their territories by diving aggressively at them. Again, the horns likely make their mobbing displays appear more threatening.
Migration
Some evidence indicates that males arrive earlier than females at the breeding grounds in spring to establish territories. This may be related to their need to display horns to attract mates.
How do horned larks use their horns?
Male horned larks utilize their showy feather horns in several key ways:
Courtship displays
During courtship, males fly high up and sing before diving steeply down with horns and wings spread wide. The horns accentuate this display for impressing females.
Territory defense
The horns help males look more threatening and dominant when facing off against rival males intruding on their territories.
Communication with other males
Males judge the fitness of competitors by looking at their horn size and darkness. They can often avoid physical confrontations this way.
Species recognition
The distinctive horns allow the larks to recognize their own species rapidly when flying or at a distance.
Camouflage (?)
One potential use is camouflaging the head against the ground when feathers are flattened down. But this is uncertain.
When are the horns displayed?
Male horned larks exhibit their horns most prominently during:
Breeding season
Courtship displays, territory defense, and competition for mates.
Territorial disputes
Confrontations with rival males year-round.
Predator mobbing
Diving at intruding predators in their territories.
The horns are displayed less the rest of the year after breeding duties end. But they still mark the males and allow for species and gender recognition outside of the breeding season.
Do any other birds have similar horns?
Horned larks aren’t the only birds to sport ornamental feather horns or crests on their heads. Some other examples include:
Cassin’s sparrow
Males have a grey crown with a forward-curving black crest used to signal dominance.
Common flameback
This tropical woodpecker has a large backwards-curving red crest used in mating displays.
Palm cockatoo
Males of this Australian parrot have an erectile crest of feathers on their heads.
Rhinoceros hornbill
This Asian hornbill has an actual hollow horn-like structure called a casque on its bill.
Andean cock-of-the-rock
Males sport a prominent half-moon crest which plays a role in mating.
However, few birds have feather crests quite like the distinctive horns of the aptly-named horned larks.
Conclusion
Male horned larks sport unique feather “horns” that likely evolved mainly for courtship displays and signaling dominance. Their horns help them attract mates, defend territories, and communicate with rivals.
Displaying horns comes with tradeoffs, so females horned larks do not grow ornamental head feathers. The horns are costly to produce and increase predation risk for females. They only benefit males by increasing reproductive success.
The tiny feather horns cause outsized changes in horned lark behavior. Males sing more, act more aggressive, and migrate earlier thanks to sexual selection for showy plumes. These horns illustrate how even modest display features can drive the evolution of differences between males and females of the same species.