It's possible that male bee hummingbirds evolved to be much smaller than females so they could perform more elaborate courtship flights thanks to their petite size.
It is possible that males of certain species of hummingbirds have undergone evolutionary changes that have caused them to be smaller than their female counterparts. This permits the males to put on more attractive courtship displays.
The phenomenon known as sexual dimorphism, in which the sexes of an animal differ in size and appearance, is widespread across the evolutionary tree. When size differences exist between the sexes, as they do in mammals and birds, the males are often the larger of the two. However, this is not the case with a species group that consists of very small bee hummingbirds, as the pattern is inverted in this case.
Sean Wilcox, who is now a professor at Moorpark College in California, and Christopher Clark, who is a professor at the University of California, Riverside, decided to examine possible evolutionary reasons for the mystery of these little males.
The researchers took information from previous studies on both sexes of 92 different species of hummingbirds and collected it into one set. The information included body mass and the rate at which the wings beat when the birds were hovering. They also obtained information on adaptations for flight, such as the length of the wings and the sternal keel, which is a massive bony protrusion from the bird's breast where powerful flight muscles attach. In addition, they measured the wings' spans. The researchers looked at 30 different species of bee hummingbirds and recorded the frequency of wing beats made by the males while they engaged in the courtship behaviours of shuttling and diving.
They discovered that male bee hummingbirds are not only physically smaller than females, but that the males also have proportionally shorter wings that beat more quickly. Additionally, their keels are longer than those of the females, which allows them to support larger muscles. When it comes to courting flights, the species whose wings are very small and have particularly long keels also have the fastest wings.
According to the data, it appears that discerning females may have been the driving force behind the evolution of males' flight sports, as well as their tiny stature.
Wilcox believes it is unlikely that conflicts between males are the cause of their small size and nimbleness; yet, it is possible that this is the case. “The majority of the study on fighting behaviour in hummingbirds has showed that larger males tended to do better,” he says. “This is especially true when it comes to defending their territory.”
If females are selectively picking out the smallest aerial aces, it is not yet known which aspects of the presentations are the most essential to them. According to Wilcox, “We Really Don't Know If Females Are Watching Males for How Quickly They Fly or If They Are Just Paying Attention to the Speed of the Wings.”
Wilcox is particularly taken aback by the strong wing beat speeds that he and Clark measured. Some males hover at 100 beats per second, and they reach 132 beats per second when they are engaging in courtship dives. Up until recently, the maximum rate of 80 heartbeats per second that was thought to be possible for hummingbirds was validated by scientific investigation.
Wilcox describes the behaviour of the birds as “flying side to side, they're cutting these turns, and ramping up their wing beat frequencies.” While they are putting on these exhibitions, are they getting close to their limits in terms of muscle performance or flight?
Wilcox claims that certain bee hummingbirds have a specialised sort of muscle, and he is curious as to whether or if the unique muscle fibres that these birds possess evolved as a result of a selective pressure to do increasingly remarkable aerial manoeuvres.
There are some species of hummingbirds, according to Derrick Groom of San Francisco State University in California, in which the males do not depend on shuttling and diving during the courtship process; rather, they gather in groups known as “leks” and compete with one another for the attention of females that happen to be in the area. According to him, it would be fascinating to examine the similarities and differences between the wing adaptations of these males and those of bee hummingbirds.