Bowerbirds are a family of small to medium-sized passerine birds native to Australia and New Guinea. The males of many bowerbird species build elaborate structures called bowers to attract females. These bowers are one of the most remarkable examples of construction behavior in the animal kingdom.
What are bowers?
Bowers are structures built by male bowerbirds to attract females for mating. They are not nests, but rather serve as a location for the male to display its colorful plumage and perform courtship dances to visiting females. The bower locations are aggressively defended by the males.
Bowers come in a variety of shapes, sizes, and building materials depending on the bowerbird species. Some of the major types of bowers built by bowerbirds include:
- Avenue or maypole bower – Two walls of vertically arranged sticks opening out to a cleared court area with decorations scattered around.
- Hut or avenue-hut bower – A chamber of loosely thatched sticks with an avenue extending out from the entrance.
- Tower or spire bower – A conical tower of sticks often with a court area used for displays.
- Mound bower – A mound of freshly cut grass stems or herbs with decorations on and around it.
The simple avenue type bowers are built by the larger bowerbirds in the genus Chlamydera. The more complex hut and tower bowers are constructed by the smaller bowerbirds of the genera Amblyornis, Archboldia, and Prionodura. Different bower designs likely reflect both the aesthetic tastes and the physical capabilities of particular bowerbird species.
What materials do bowerbirds use?
Bowerbirds use a wide range of materials for the construction of their bowers. The materials used depend on what is available in their habitats but often include:
- Twigs and sticks
- Herbaceous stems and vines
- Bark strips
- Moss
- Fresh greens and flowers
- Pebbles
- Colorful man-made items like glass and plastic
Larger sticks and twigs form the main structural framework of many bowers. Softer herbaceous stems, vines, moss, and bark strips are used as binding material to loosely weave or glue the main sticks together. Greens and flowers are used decoratively in some bower designs.
Many bowerbird species also incorporate colorful man-made objects like glass beads, plastic bottles or cutlery scavenged from human litter into their bowers. The color intensity of these items attracts females. The blue satin bowerbird even preferentially seeks out blue objects!
How complex can bowerbird bowers get?
The bowers of some bowerbird species are incredibly complex and elaborate structures. Here are some examples of the most complex bower designs:
- The maypole bowers built by the fawn-breasted bowerbird can be up to 9 feet tall! Thousands of sticks and tens of thousands of decorations may be used in a single bower.
- Vogelkop bowerbirds build thatched hut bowers with an inner cone of sticks can that measure over 7 feet wide at the base. The entrance avenue is decorated with thousands of colorful fruits, flowers, beetle wing cases, and snail shells.
- The tiny golden bowerbird builds tightly woven stick towers up to 60 cm high on saplings. The towers are clad with lichens and decorated with hundreds of snail shells.
The exact structure, size, materials and decorations used are unique to each male bowerbird. Females inspect multiple bowers before choosing a mate, so the quality and complexity of the bower plays an important role in courtship.
How do bowerbirds build their complex bowers?
Bowerbirds have some remarkable adaptations and behaviors that allow them to construct their complex bowers:
- Instinctual building knowledge – Juvenile males develop the instinct to build species-specific bower designs without ever being taught.
- Acute color vision – Their eyes have specialized color receptors to help find decorations of specific hues.
- Powerful object memory – They can remember the locations of thousands of objects used as decorations around their bowers.
- Highly coordinated construction – Their beaks and feet allow intricate placement and weaving together of materials.
- Male cooperation – Some species cooperate on bower building and share decorations, improving the structure.
The bowerbird brain contains large expansion of areas responsible for visual processing, object memory, and coordination. This gives them the unique cognitive tools needed to create their elaborate bowers.
Why do bowerbirds build bowers?
Male bowerbirds construct bowers for the sole purpose of attracting a female mate for breeding. The bower serves as a location to display to visiting females.
Building an attractive bower signals that the male has good genes because bower construction takes energy, skill, cognition, and survival. Females inspect bowers and mate with males that build the best ones.
Specific evolutionary pressures that may have led to the behavior include:
- Female preference for good nest builders – Females that mated with skilled nest builders had healthier offspring.
- Competition between males drove elaboration – Females favored more decorated bowers, fueling males to compete.
- Cognition developed to build better bowers – Mental skills evolved to construct and decorate bowers.
Whatever their origins, bowers are now deeply ingrained in bowerbird courtship. Males incapable of building bowers often fail to attract mates in the wild.
How do female bowerbirds choose a mate?
When female bowerbirds visit a bower, they carefully assess both the structure and the male owner before choosing whether to mate. Females evaluate bowers for features including:
- Size – Larger bowers signal a fitter male.
- Craftsmanship – Intricate weaving and symmetry show skill.
- Quantity of decorations – More decor reflects greater effort.
- Rarity of decorations – Unique or unusual objects stand out.
- Orderliness – Neat, organized placement of objects.
Females also assess courtship displays and appearance of the male. But the bower itself acts an extended phenotype of the male’s fitness. Males with damaged bowers often get rejected.
By choosing males based on bowers, females likely gain these benefits:
- Good genes for their offspring – Building requires fitness.
- Superior parental care – Nest construction skills.
- Mental fitness – Higher cognition in mate choice.
- Avoiding disease – Rejecting unfit males.
This choosy strategy allows females to select genetically superior mates capable of providing benefits to their young.
Do bowerbird males and females ever share in raising young?
No, bowerbirds show essentially no parental care from the males. Only female bowerbirds care for the young after eggs hatch:
- Females build the actual nests alone with no male assistance.
- Females incubate the eggs alone for roughly 3 weeks until they hatch.
- Females brood and feed the nestlings on their own for several weeks.
- Males provide no food or protection to the fledglings.
This uniparental care by the female is likely why male bowerbuilding evolved in the first place. Males must attract females with bowers but do not help raise young after mating.
The female-only care also means males can mate with multiple females in a breeding season. Males focus entirely on bowerbuilding and courting additional mates rather than helping with offspring.
Conclusion
The bowers built by male bowerbirds are some of the most fascinating and complex constructions made by animals. From the towering maypole bowers to the ornamented fruit mounds, they represent an incredible evolutionary achievement. The skills and aesthetics of the females select for males that build ever more elaborate bowers. This has driven male bowerbirds to excel at constructing and decorating intricate structures just to find a mate. Their bowers stand as exotic monuments to the power of sexual selection and competition to spur remarkable adaptations in nature.