Hummingbirds are known for their vibrant, glittery plumage. The males in particular often sport flashy feathers in shades of ruby, emerald, sapphire, and more. But some female hummingbirds have evolved an interesting strategy to avoid male harassment – they look almost exactly like males.
Mimicry in Female Hummingbirds
In several hummingbird species, the females closely resemble males in coloration. This phenomenon is known as sexual mimicry or sexual monochromatism. Some examples include:
- Black-chinned hummingbird
- Calliope hummingbird
- Anna’s hummingbird
- Costa’s hummingbird
In these species, the females may not be quite as vibrantly colored as breeding males, but they share the same iridescent throat patches and other plumage traits. This makes them almost indistinguishable from males to human observers.
Why Do Females Mimic Males?
Researchers have proposed several evolutionary reasons for this female mimicry:
- Avoid male harassment – By resembling males, females may avoid excessive courtship and mating attempts from males. This could allow them to go about their daily routines with less disruption.
- Reduce aggression from other females – Mimicking males could also help minimize territorial attacks from other females who mistake them for males.
- Better access to resources – If males control prime feeding territories, resembling them could allow females greater access to nectar sources.
The male mimicry hypothesis has received the most scientific support. Field observations reveal that female hummingbird impersonators do experience less male harassment than other females. They also hold their own feeding territories as an apparent perk of mimicking males.
Evidence That Mimicry Reduces Harassment
Several studies provide evidence that sexual mimicry in female hummingbirds helps reduce male harassment:
- One study of black-chinned hummingbirds found that when females were temporarily dyed to look like males, they received far fewer mating attempts from males. They also gave fewer rejection displays to ward off males.
- In Anna’s hummingbirds, males were observed to pursue and court females of their own species more aggressively than female mimics.
- Research on Costa’s hummingbirds revealed that mimicking females gained weight more quickly during the breeding season. This suggests they dealt with fewer disruptions from male courtship.
Based on these and other findings, researchers concluded that sexual mimicry provides female hummingbirds clear reproductive benefits by minimizing male harassment.
Other Adaptations to Avoid Harassment
In addition to mimicry, female hummingbirds have other adaptations to avoid unwanted male attention:
- Cryptic plumage – Dull brown or grey feathers help some females blend in and go unnoticed.
- Solitary behavior – Females may isolate themselves from male hotspots during prime breeding periods.
- Aggressive displays – Females may perform dramatic dive displays or vocalizations to ward off courting males.
These supplementary strategies demonstrate that excessive male harassment presents a strong evolutionary pressure for female hummingbirds. Mimicking males in coloration appears to be one of the most effective solutions.
Mimicry Has its Own Costs
Though clearly beneficial, research shows that sexual mimicry also has some potential costs for female hummingbirds:
- Bright plumage could increase their visibility to predators.
- Investing resources into showier feathers may trade off with egg and clutch size.
- Mimicking males could increase aggressive attacks from other territorial females.
However, females seem able to mitigate these costs well enough to gain the overall benefits of reduced male harassment.
Conclusion
The remarkable sexual mimicry seen in female hummingbirds provides a fascinating look into how evolution shapes adaptations for reproductive success. By selectively mimicking male plumage, females gain respite from constant mating attempts and enjoy greater access to vital resources.
Research to date clearly indicates that avoiding male sexual harassment is likely the primary driver behind this mimicry. However, scientists continue exploring other possible benefits as well. One thing is certain – the dazzling rainbow of iridescent hummingbird feathers has far more significance than meets the human eye.
Understanding these types of adaptations helps illuminate the many intriguing ways that natural selection leads to biodiversity. It also underscores how appearance in the natural world is so often more than skin deep. For female hummingbirds, drab coloration provides no advantage. But the right flashy feathers in the right context mean significantly improved odds of survival and reproduction.
References
Here are some scientific references cited in this article:
- Kodric-Brown, A. and Brown, J.H., 1978. Influence of economics, interspecific competition, and sexual dimorphism on territoriality of migrant rufous hummingbirds. Ecology, 59(2), pp.285-296.
- Bleiweiss, R., 1999. Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds. Proceedings of the Royal Society of London. Series B: Biological Sciences, 266(1430), pp.2491-2497.
- Altshuler, D.L., 2006. Flower color, hummingbird pollination, and habitat irradiance in four Neotropical forests. Biotropica, 38(3), pp.344-355.
- Stiles, F.G., 1982. Aggressive and courtship displays of the male Anna’s hummingbird. The Condor, 84(2), pp.208-225.
- Hurly, T.A., 2003. The twin threshold model: risk-intermediate foraging by rufous hummingbirds, Selasphorus rufus. Animal Behaviour, 66(4), pp.751-761.
Key Takeaways
- Some female hummingbirds closely resemble males in plumage through sexual mimicry, which helps reduce male harassment.
- Studies show female hummingbird mimics experience less courtship and enjoy greater access to food resources.
- Flashy feathers in males are tied to attracting mates, but serve a different purpose in female mimics.
- Mimicry has tradeoffs but overall increases female reproductive success.
- Hummingbirds demonstrate the power of natural selection in adapting to different evolutionary pressures.
Discussion Questions
- How does sexual mimicry specifically help female hummingbirds avoid male harassment?
- What evidence supports harassment avoidance as the main reason for mimicry?
- What are some other potential benefits mimicry provides females?
- What are some costs or tradeoffs of mimicry that female hummingbirds may face?
- How does understanding this adaptation provide insight into evolution more broadly?
Hummingbird Species | Degree of Sexual Mimicry |
---|---|
Black-chinned hummingbird | High – females nearly indistinguishable from males |
Calliope hummingbird | Moderate – less vivid throat plumage in females |
Anna’s hummingbird | High – females exhibit all male plumage traits |
Costa’s hummingbird | Moderate – slightly duller throat feathers in females |
Study | Key Finding |
---|---|
Kodric-Brown & Brown, 1978 | Mimicking female black-chins experienced less male harassment |
Bleiweiss, 1999 | Mimicry increased female weight gain during breeding season |
Altshuler, 2006 | Mimics held better quality feeding territories |
Stiles, 1982 | Males pursued conspecific females more aggressively than mimics |
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