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Fig. 3.12
Intersong
variability expressed after a
playback experiment on
caged males of nightingale
(
Luscinia megarhynchos
).
Solo singing refers to songs
spontaneously produced
without playback
(Reproduced with
permission from Brumm
2006
)
5
4
3
2
1
0
Solo singing
Playback
3.5 The Species Recognition Hypothesis (SRH)
Between the different hypotheses that are in action in the natural selection arena,
the species recognition hypothesis (SRH) supposes that species living in sympatry
try to reduce the risk of utilizing similar sonic traits that could confound species in
reproduction, thus increasing the risk of hybridizations.
The species recognition hypothesis has been confirmed in neotropical suboscine
passerines in which the song of sympatric pairs of closely related species has a more
divergent acoustic pattern than that of allopatric pairs (Seddon
2005
).
Definitively, three hypotheses have been tested by Seddon (
2005
): the morpho-
logical adaptation hypothesis, the acoustic adaptation hypothesis, and the species
recognition hypothesis, by studying a group of antbirds (
Thamnophilidae
). These
birds are ideal subjects because their songs are not culturally influenced by learning,
have a very simple loudsong, and the differences in song performance can be
associated with variation of environmental conditions.
According the species recognition hypothesis sympatric species should have a
more distinct song repertoire than allopatric species. We define sympatric species as
species that are living in the same habitat and overlap at least 25 %. Allopatric
species are species that live in habitats that are geographically separate.
In this investigation, Seddon has found that bill morphology was positively
correlated with the dimension of birds, according to the morphological adaptation
hypothesis, but that also the other two hypotheses were confirmed. This finding
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