By Mary Lou Hoffacker, Mikayla Kelly, Gilly Mangan
Through the dense, vine-covered understory of the Australian rainforest, male birds flutter around, looking through the trees for something special. Suddenly, one will find a perfect leaf and take it home, meticulously placing on the cleared space he’s been working on his whole life. There, he will wait for potential mates to come and inspect his work, constantly hoping that she will choose him. These birds are tooth-billed bowerbirds (Scenopoeetes dentirostris), a bird species only found in the Wet Tropics World Heritage Area. The Wet Tropics are a protected area of tropical rainforest habitat that spans across North Queensland, Australia, and is home to many species not found anywhere else in the world. Scattered specifically across the Atherton Tablelands, these male bowerbirds perform their courtship rituals, leaving their mark on the rainforest and giving opportunity to study the inner dynamics of bird communities.
Tooth-billed bowerbirds are medium-sized, stocky birds with an olive back and speckled underside. The species is part of a larger family (genus Scenopoeetes) of bowerbirds, all of which perform elaborate courtship rituals to attract mates. Unlike most species Photo courtesy of Mary Lou Hoffacker. A tooth-billed bowerbird stage found on the northern end of Lake Eachamof bowerbirds which construct elaborate structures of twigs, the male tooth-billed bowerbirds create a stage. The stage is placed by a prominent display tree, can be meters long and usually has leaves meticulously placed with the pale underside facing upwards. Once the stage is built, the male bower will sit on a perch near the stage and sing, waiting for a female to appear. When a female approaches to inspect the bower, the male performs elaborate dances and mimicry calls in hopes of being chosen as a mate.
Even though all tooth-billed bowerbirds create stages, the specific rainforest area a bird lives in affects the appearance of the stage. A possible explanation for the varying appearances could be the cultures of the bird communities in the different locations. Culture, in this case, refers to the behaviors that a group of animals have learned and exhibit in a specific geographical area. It is possible that females in a bowerbird community all like the same kind of stage. The males in that area, longing to find a mate, would learn over time to create that specific style. In order to examine how bird culture can change, if at all, the appearance of the bird’s bower, a single-day observational study was performed in six different sites. Each site utilized the same rainforest type, around the Atherton Tablelands west of Cairns. In each site, surveyed by a separate group of three or four study abroad students, the distinctive mating call of the bowerbird was used to locate the stage of that bird. Once the stage was found, measurements such as the size of bower and vegetation used were taken, as well as information about the display tree. At the end of the survey, data of all the stages found in each site was averaged in order to allow comparison of sites.
Four of the sites surveyed were part of Lake Eacham National Park, with the two remaining sites being located in Lake Barrine National Park and Gadgarra National Park. Overall, there were some differences noted in the bowers of different bird communities across the sites. The birds at the Lake Eacham sites chose display trees (the prominent tree at the end of a stage) that were 1.5cm smaller in diameter than the trees at the other sites. The stages at Gadgarra were approximately 30cm smaller in length than the stages at all other sites. At the Lake Barrine site, the stages were constructed with far fewer leaves. They only had 36 leaves on average, compared to around 70 leaves found at the rest of the sites. While all these differences were observed, the reasoning behind the varying structures is still unclear.
A possible explanation for the observed differences could be the culture of bird communities. The rainforest in each of the sites was the same type, meaning the same trees and vegetation were at least somewhat available. As a result, differences in bowers could reflect a preferential selection by the females of the community. If this truly happens, bird communities could be analyzed in a completely different fashion than one that just looks at resources available. The desires and preferences of birds are thus much more important, adding a new dimension to the world of scientific research. In the meantime, the lonely bowerbird will continue arranging and rearranging his stage, hoping that someday he’ll find true love.
Sources:Slater, P., Slater, P., and Slater, R. (2009) “The Slater Field Guide to Australian Birds.” Reed New Holland: Syd-ney.“ TOOTH-BILLED BOWERBIRD.” Rainforest-Australia. 2009. Web. 9 Oct. 2015.