Hummingbirds are known for their brightly colored, iridescent feathers. The males in particular often sport gorgeously colored throats and feathers in order to attract females. However, in some species, the females also develop bright, male-like plumage. This phenomenon has puzzled scientists for decades. In this article, we’ll explore the leading theories behind why some female hummingbirds mimic male plumage and behavior.
In over a dozen species of hummingbirds, females possess the same iridescent throat patches and colorful plumage that males display. Additionally, they may mimic male behavior such as aerial dive displays. This is surprising because in most bird species, the males bear the more vivid feathers in order to attract females. Why would female hummingbirds, who don’t need to attract mates, evolve these types of elaborate feathers? There are a few leading hypotheses that scientists have proposed:
- Mimicry helps minimize harassment from males
- Mimicry enables females to disrupt potential mating competitors
- Mimicry gives females access to better feeding territories
Researchers are still investigating the validity of these different explanations. It’s likely that the reasons behind this reverse plumage dimorphism are complex and involve multiple factors. In this article, we’ll take a deeper look at each of these hypotheses.
Hypothesis 1: Mimicking males helps minimize harassment from males
One leading theory is that female hummingbird plumage mimicking helps minimize harassment from males. Male hummingbirds can be quite aggressive when defending their territory or pursuing mates. Females who stray into another male’s domain may get chased out. However, if the trespassing bird appears male, this signaling helps avoid an attack. Researchers hypothesize that females gain a selective advantage by mimicking males and avoiding excessive harassment.
There is some evidence to support this theory. Experiments with Anna’s hummingbirds revealed that when researchers altered female tail and crown feathers to resemble a male’s, territorial males were less likely to exhibit chase behavior towards them. Additionally, observations of Costa’s hummingbirds demonstrated that males were more aggressive toward females with clipped iridescent throat feathers versus intact feathers.
While mimicking male plumage seems to reduce antagonistic behavior, some questions remain. For example, many female hummingbirds only develop partial male-like plumage rather than full mimicry. Researchers still do not fully understand how incomplete mimicry would help minimize harassment or deter males.
Hypothesis 2: Mimicry enables females to disrupt potential mating competitors
Another hypothesis states that female hummingbird mimicry helps disrupt potential mating competitors. By mimicking male plumage, females can more easily slip into another bird’s territory undetected. Once inside, the female can observe potential threats – rival females that the territory-holding male may mate with. Then, the imposter female can disrupt these pairs from mating by chasing them off or intimidating them with displays.
Essentially, mimicry enables females to more easily infiltrate a desirable male’s territory to observe and even thwart any mating competitors. This indirectly benefits her by directing the male’s mating attention towards herself. There is some evidence that hummingbird females do use mimicry in sneaky ways to obtain access to territorial males. For example, researchers observed female rufous hummingbirds entering and exploring male territories while displaying partial male plumage.
However, more observations are likely needed to determine if females use mimicry with the specific intent of disrupting mating competitors. Females may also gain other advantages through mimicry and infiltration such as better access to food resources. More research is required to understand the nuances of this hypothesis.
Hypothesis 3: Mimicry gives females access to better feeding territories
The third major hypothesis states that male-like plumage in females enables access to superior feeding territories defended by males. In many hummingbird species, the males establish and occupy the highest quality territories with abundant food resources. By mimicking male plumage, females can avoid excess harassment from territorial males, allowing them to temporarily share in these plentiful resources.
There is some good evidence demonstrating that mimicry does help improve feeding access for females. Experiments with rufous hummingbirds revealed that when females were altered to have male-like plumage, they were able to feed at higher quality and more contested sites. Additionally, observations of Anna’s hummingbirds showed that mimicry allowed females to spend more time feeding on high value food sources in a male’s territory.
This research lends support to the idea that accessing superior food resources is a key advantage of mimicry that led to its evolution. However, scientists acknowledge that mimicry likely serves multiple purposes. The various hypotheses are not mutually exclusive, and the benefits of mimicry probably encompass different factors related to minimizing harassment, disrupting mating competitors, and gaining feeding access.
Key Examples of Hummingbird Mimicry
There are several species of hummingbirds that exhibit female mimicry of males. Here are some of the key examples that have helped inform research on this phenomenon:
Rufous Hummingbird
In the rufous hummingbird species, the females possess orange-red throat feathers and some iridescent plumage that closely resembles the males. They exhibit the most complete mimicry among hummingbirds. Researchers have extensively studied this species to understand the impacts of mimicry on mate competition, aggression, and feeding.
Anna’s Hummingbird
Female Anna’s hummingbirds develop rose-pink throat patches and some elongated head feathers that parallel male plumage. However, it is intermediate mimicry. Studies on this species provided early evidence that male-like feathers help minimize harassment from other males.
Costa’s Hummingbird
The female Costa’s hummingbird has iridescent purple throat feathers similar to the male, but otherwise lacks mimicry of the male’s striking purple crown. Research on Costa’s hummingbirds demonstrates that strongly iridescent throats help deter males, even without full mimicry.
Black-chinned Hummingbird
In Black-chinned hummingbirds, the female throat plumage can range from mostly white (non-mimicry) to quite iridescent and purple (mimicry). Interestingly, the degree of mimicry corresponds to aggression received from males, providing support for the harassment avoidance hypothesis.
These are some of the most relevant species displaying female mimicry of male hummingbird plumage. The variety and degree of mimicry help reveal insights into how these traits may have evolved.
Evolutionary Origins of Mimicry
Researchers are still working to uncover the evolutionary origins of female hummingbird mimicry. There are a couple leading theories about how this reverse plumage dimorphism may have developed:
Physiological Link Hypothesis
One idea is that female mimicry arose from physiological links between male and female coloration. In many bird species, feather colors stem from similar developmental pathways in both sexes. For example, in European barn owls, a genetic mutation led to higher levels of melanin that turned male plumage darker. Females also became darker due to their shared physiological pathways.
In hummingbirds, certain physiological processes may have first led to more vivid male plumage, and females started developing similar colors as a byproduct. If this bright plumage then gave females an advantage through one of the mimicry benefits described earlier, it could have been naturally selected for.
Male-Like Behavioral Traits
Another hypothesis is that certain male-like behavioral traits evolved in females first, preceiving selection for male-like plumage. For example, if food competition led to females developing aggressive territorial behavior similar to males, this may have then favored the evolution of female mimicry. By first looking and acting somewhat like males, full mimicry of plumage could have followed.
In reality, both physiological factors and behavioral traits were likely at play in a complex, interdependent evolutionary process. But these hypotheses aim to provide a logical sequence of events that could have led to the emergence of female hummingbird mimicry.
Mimicry in Other Female Bird Species
While especially prevalent in hummingbirds, female mimicry of elaborate male plumage also occurs in some other bird groups as well. Here are a couple examples:
Phainopeplas
In the phainopepla species of the silky-flycatcher family, females develop a black crest and black wings that closely resemble the male’s coloration. The mimicry likely enables females to gain access to fruiting resources defended by territorial males.
Paradise Whydahs
Female paradise whydahs exhibit an intermediate mimicry of male breeding plumage. Their duller black feathers probably help them access nesting sites secured by males while avoiding excessive male harassment.
Researchers can gain additional insights into the advantages of mimicry by studying parallel phenomena in other female bird species. However, hummingbirds do represent the most extensive and striking known example of this reverse plumage dimorphism in the avian world.
Remaining Questions
While substantial progress has been made, many questions still remain around why female hummingbirds mimic male plumage:
- How exactly does intermediate or imperfect mimicry confer advantages to females?
- What genetic changes enable mimicry to arise in females?
- How do the different benefits of mimicry interact and vary across species?
- Why do only certain hummingbird species show mimicry while most do not?
- How does male behavior and plumage co-evolve in response to female mimicry?
Upcoming research using genetic analysis, field experiments, and behavioral observation will continue unpacking the complex evolutionary drivers behind hummingbird mimicry. As scientists fill in these knowledge gaps, we can gain deeper insight into the ecological factors that drive the development of elaborate animal colors and signals.
Conclusion
The phenomenon of female hummingbirds evolving male-like plumage has long captivated researchers. After decades of study, modern science has provided significant evidence around the potential benefits of mimicry related to harassment avoidance, sexual competition, and food access. However, many details are still unknown about how exactly mimicry provides advantages, the genetic changes enabling it, and the complex co-evolution between males and mimicking females.
Understanding these unique gender dynamics in hummingbirds can reveal valuable insights into evolutionary biology. As scientists continue probing this mystery of reverse plumage dimorphism, we can further unravel the forces driving biodiversity across the animal kingdom.
