Meeting Abstract

P1.121  Jan. 4  Bower orientation in satin bowerbirds: the sun gets in their eyes? BURCH, E.; HIEBERT, S.M.**; Lower Merion High School, Ardmore, PA; Swarthmore College, Swarthmore, PA

Male satin bowerbirds (Ptilonorhynchus violaceus) construct an avenue bower in which the female stands to watch the male perform courtship displays and to copulate with him. Bowers built by members of the southern population of this species are typically oriented northward, and males will quickly dismantle experimentally rotated bowers and rebuild them in the preferred orientation. However, the question of why bowers are oriented in this direction remains unresolved. To test the often-cited hypothesis that northward bower orientation prevents the male and female from being blinded by sunlight during early morning courtship, we assessed canopy cover over bowers that we located in coastal rainforest habitat from southern New South Wales to southern Queensland, Australia. Average orientation of these bowers was 16 ± 29 ° (N = 61) . Photographs of the canopy were taken from a camera placed at the bower and oriented upward at angles corresponding to the path of the sun as it would travel across the sky throughout the day on the spring equinox and on the summer solstice at that location. Photographs were obtained for sun angles corresponding to sunrise through 1300 h from 15 of these bowers, and from sunrise to sunset from an additional 39 bowers. Image analysis software (ImageJ) was used to determine the percent sky cover in a 14 ° ribbon centered on the estimated path of the sun in each photograph. The very low percent visible sky measured in these photographs, especially in early morning, is inconsistent with the “blinding” hypothesis, suggesting that an alternate explanation is needed to account for the nonrandom bower orientation in this species.