On Sat, Apr 08, 2006 at 06:23:44PM +1000, Alan Gillanders wrote:
> As the bowers are double ended I find this a hard one to fathom.
I have to apologize - if I'd read on I'd have found some material
in the Emu paper very relevant to the discussion:
"Bower orientation is defined as the compass direction (relative to true
north) of a line drawn parallel to the bower walls from the center of the
avenue to the decorated portion of the platform where the male displays
(Fig. 1). It has been well documented that, at least in the southern race
of Satin Bowerbirds, males tend to orient their bower avenues along a
north-south axis, with the decorated portion of the platform at the north
end (Chaffer 1931; Marshall 1954; Borgia 1995a). Chaffer (1931) noted that
most bowers he observed in National Park, New South Wales, were oriented
northward. Marshall (1954) likewise observed that, among 60 bowers he
located over several years, the deviation from a northern orientation
was never more than 30 degrees. When he experimentally reoriented bowers
by as little as 15 degrees, the bower owner would promptly demolish the
bower and rebuild it on its original bearing (Marshall 1954). Similarly,
Borgia (1995a) reported the mean orientation of 36 bowers at Wallaby
Creek, New South Wales, as 2.7 degrees+- 31.0 (mean +- s.d.)
Great Bowerbirds, Chlamydera nuchalis, also generally orient their bowers
along a north-south axis (reviewed in Frith et al. 1996). In contrast,
Spotted Bowerbird, Chlamydera maculata, males build their bowers along an
east-west axis (Borgia 1995a). However, in this species, the bower walls
are constructed from straw rather than twigs, and females can observe
displaying males through one of these walls. Accordingly, male Spottted
Bowerbirds spend the largest proportion of their time displaying at the
north end of the bower (Borgia 1995a)."
Ref. details and abstract at:
http://www.publish.csiro.au/nid/96/paper/MU02024.htm
Andrew
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