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Figure 1. Satin Bowerbird at his bower

The bowers made by Bowerbirds are what makes them such interesting creatures. Male Bowerbirds create different types of bowers, and decorate them very uniquely in attempt to attract females. These birds decorate their bowers with anything colourful they can find such as flowers, berries, and rocks. Females will often spend their time looking at many different males bowers in attempt to find the one they believe looks the best. It is thought that the nicer the males bower looks, the greater offspring they will produce. After the birds mate, the female will leave the males bower to create her own nest where she will give birth to their offspring.

Figure 2: Example of an avenue bower, painted with orange pulp from fruits and vegetables.

Background information

Bowerbirds are a unique type of birds that come from the family Ptilonorhynchidae. There are roughly 20 species of this bird, and they are mainly found in Australia and New Guinea. They range in size and colour. For example, the Satin Bowerbird is characterized by shiny blue feathers that appear metallic. In contrast, the Revenue Bowerbird is mainly black with some bright orange feathers. The majority of these birds weigh from 70 grams- 250 grams. These birds live in numerous different types of environments such as shrub-land, and tropical forests. Some consider these creatures agricultural pests since their diet mainly consists of fruit.

Three types of bowers

There are three main types of bowers that male Bowerbirds will produce. The first is known as the "mat" or the "platform". This type of bower is similar to a bed. It consists of a pad of plant material. To make this pad more appealing to females, the birds will generally place all of the leafs shiny side up. Archbold's Bowerbirds generally make this type of bower. The second type of bower is called the "maypole". For this type of bower, the bird creates two towers of twigs, and forms an arch on top to protect the birds. The golden Bowerbird generally creates this bower using tree moss, and decorates it with flowers and berries to try to catch the females attention. The final type of nest created by Bowerbirds is called the "avenue" and is created by Satin Bowerbirds. This bower is larger than the others, and the bird creates a hollow cylinder made of twigs. These types of bowers are painted with vegetable pulp, charcoal, and saliva and applied to the walls.

Bower illusions for attracting mates

Bowerbirds create these bowers the way they do for multiple reasons. The first of which, is to attract females. Female Bowerbirds will often spend their time looking at multiple bowers, to see which one attracts them the most. Females believe that the quality of the males bower is an indication of the males fitness. Little do the females birds know, much of the male bower is an illusion.Male Bowerbirds arrange their objects a particular way, they arrange the objects so that the objects have a positive size-distance gradient. To the female bird, looking from far away, all of the objects appear the same size. The illusion also makes the male appear bigger than he actually is. One group of experimenters manipulated the birds environment so the small objects would be places far away, and the large objects would be places closer to the bower.The birds generally fixed the placement of the objects within three days.

Costs and alternative ways to attracting females

There are numerous costs associated with maintaining the bowers. Often times male Bowerbirds will steal from other bowers, some may even attempt to completely destroy others bowers. Since the quality of the males bower is important for sexual reproduction, it is critical that the male Bowerbirds maintain their bowers to the highest standard. Another thing to consider is the availability of decorations. It is said that a single bower may contain from 30 to more than 12,000 decorations . Some environments may not have enough decorations for the amount needed, thus increasing competition . Not only do these birds need to find decorations and guard their property to inhibit stolen decorations, they have to constantly replace some decorations that may die or wilt such as flowers and berries. If the bower created by the male is not sufficient in attracting the female, the male may start to sing and wave around items to attract the female. If the female gets close enough, the female may become distracted enough so the male can mate her.