Biology Reference
In-Depth Information
(a)
(b)
35
24
Fig. 7.8 Female
choice for good
resources. (a) Female
hanging flies
( Hylobittacus
apicalis ) mate with
males for longer if
the male brings a
larger prey item for
her to eat during
copulation. (b) The
male benefits from
long copulation
because he fertilizes
more eggs. From
Thornhill (1976).
20
25
16
15
12
8
5
4
0
10
20
30
40
50
1
5
9
13
17
21
25
29
33
37
Body size, length
width (mm 2 ) of nuptial prey
Duration of copulation (min)
Good genes
In some cases, all the female gets from a male is sperm to fertilize her eggs. Nevertheless,
even here females are often very choosy. Bowerbirds provide a wonderful example.
There are twenty species, all inhabiting New Guinea and Australia. In most, the males
play no part in parental care; all their reproductive effort is put into display. They use
sticks, grasses and stems to construct bowers, of various structures depending on
the species; some are in the form of little avenues, others are towers, others are little
roofed huts. The males then decorate their bowers with colourful fruits, flowers,
feathers, bones, stones, shells and insect skeletons. Some will collect man-made
objects  too, such as pen tops, bottle tops, clothes pegs, car keys, jewellery and even,
in  one case, an  old man's glass eye! The colour varies with the species; male satin
bowerbirds,  Ptilonorhynchus violaceus , prefer blue objects, while male spotted
bowerbirds, Chlamydera maculata , prefer white and green objects (Fig. 7.9). So elaborate
is the hut-like bower of the Vogelkop bowerbird Amblyornis inornatus , with its carefully
arranged separate piles of pink flowers, green moss and shiny beetle elytra, that early
explorers in New Guinea assumed these must be religious shrines built by local tribes
people (Fig. 14.8c; Frith & Frith, 2004).
Females visit bowers solely for mating, and in both satin bowerbirds (Borgia,
1985) and spotted bowerbirds (Madden, 2003a) it has been shown that males with
the best decorated bowers gain the most matings. In satin bowerbirds, experimental
removal of the decorations reduced the male's mating success (Borgia, 1985).
In  spotted bowerbirds, choice experiments revealed that males preferred to add
to  their bowers those objects which were best predictors of mate attraction,
especially green Solanum berries (Madden, 2003b). Males often steal decorations
from neighbouring bowers and they also sometimes destroy other males' bowers, so
a male's decorations may signal his ability to defend his treasures as well as his
ability to collect them. When Joah Madden (2002) added Solanum berries to spotted
bowerbird bowers, this attracted increased bower destruction from rival males.
When he removed berries and offered males excess berries to re-decorate their
But sometimes all
the female gains
from a male is
sperm
Female choice for
more ornamental
bowers in
bowerbirds
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