Biology Reference
In-Depth Information
Fig. 9.11
Once a
male pied
flycatcher has
attracted one
female, he flies off
to another nest
site some distance
away and tries to
attract another.
Secondary females
suffer because
they get little or
no help from the
male in chick
rearing. However,
females probably
are unable to
assess whether
the male they pair
with has another
female because of
the large distance
between a male's
two nest sites.
(ii)
Deception
. Alatalo
et al
. (1981) proposed that second females are deceived into
settling polygynously because the male's habit of setting up nesting territories
several hundred metres apart (polyterritoriality) prevents females from
distinguishing mated from unmated males. By the time the second female has laid
her clutch and the male has deserted her to go back to his first female, it is too late
in the season for it to be profitable to start another clutch, so she has to make the
best of a bad job and rear her offspring alone.
(iii)
Unmated males hard to find
. An alternative hypothesis is that second females are
not deceived but they choose polygyny as their best option simply because
unmated males are hard to find. According to this view, male polyterritoriality is
not to aid female deception but to decrease the chance that aggression from the
first female will prevent the second female from settling (Stenmark
et al
., 1988;
Dale
et al
., 1990).
Testing between these last two hypotheses requires detailed observations on how
females sample males and territories, and measurements of the profitability of their
alternative options. Alatalo
et al
. (1990) performed a clever experiment to test between
them. By erecting nest boxes in careful sequence, they arranged for neighbouring
boxes, less than 100 m apart, to be occupied by an unmated male and a mated male,
whose first female was incubating a clutch in another box 100-300 m away. Boxes
were put up at randomly chosen sites, so there was no difference in territory quality
An experimental
test of deception
by males
