Bowerbirds, found across Australia and New Guinea, are known for unique courtship behaviors.
The Elaborate Bower: Artistry and Purpose
Male bowerbirds construct an elaborate structure, known as a bower, to attract a mate. These bowers are not nests for raising young but stages for courtship displays. There are two primary types: avenue-type and maypole-type. Avenue bowers feature two parallel walls of vertically placed sticks, sometimes reaching up to two meters long. Maypole bowers are built by arranging sticks around a central sapling, with some species even incorporating a hut-like roof.
Males meticulously construct and decorate these structures, often spending weeks or months on their maintenance. They gather a wide variety of objects for decoration, including berries, flowers, shells, stones, feathers, and even human-discarded items like plastic and glass. These objects are often arranged by color or size to enhance visual appeal. For example, Satin Bowerbirds frequently use blue objects, while Great Bowerbirds prefer grey and white items accented with red, purple, and green.
Courtship Displays and Female Assessment
The male bowerbird uses the completed bower as a stage for courtship. These performances involve unique vocalizations, complex dances, and skillful manipulation of collected objects. Some males create optical illusions by arranging objects from smallest to largest, which can hold a female’s attention longer. The female’s role in this process is active and discerning.
Females visit multiple bowers, inspecting the construction quality, decoration arrangement, and male’s performance. Her choice of a mate is based on these detailed assessments, driven by sexual selection. Research indicates that bower quality and male dancing ability are strong predictors of mating success. Females may visit several males before selecting one, sometimes returning to the most attractive male for mating.
Beyond the Bower: Remarkable Mimicry and Other Behaviors
Beyond their architectural prowess, many bowerbird species are exceptional vocal mimics. They can imitate a wide array of sounds from their surroundings, including other bird calls, animal sounds like pigs or cats, and mechanical noises such as chainsaws or camera clicks.
Spotted Bowerbirds, for instance, mimic up to 15 other bird species and human voices. While the exact function of mimicry is not fully understood, it is often incorporated into courtship displays. Some instances, particularly alarm calls, appear to be used in response to perceived threats near their bower.
The Evolutionary Drive Behind Uniqueness
The unique traits of bowerbirds, especially their bower-building and courtship displays, are driven by sexual selection. This evolutionary process occurs when individuals with certain traits gain an advantage in mating success. Females actively choose mates based on bower quality and display, leading to the evolution of complex structures and behaviors.
The bower and male’s performance signal his fitness and resourcefulness. Building and maintaining a bower requires significant time, energy, and skill, indicating a male’s ability to gather resources and avoid predators. This display acts as an honest signal of the male’s quality. The ability of males to adjust display intensity in response to female signals also plays a role in courtship success.