Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 87

Fig. 4.10 Relationship
between the amount of
“snarr” in the song of the
water pipit ( Anthus
spinoletta ) and male body
weight (Reproduced with
permission from Rehsteiner
et al. 1998 )
being uttered, although acoustic performance is not sufficient to explain male
reproductive success and other characteristics aside from song quality concur to
this success, such as time spent singing, song rate, length and amplitude, etc.
In birds like starlings ( Sturnus vulgaris ) and in Acrocephalus warblers the
females select the males with the broadest repertoire, where the repertoire size is
defined as the number of different elements of song that a male can produce.
In sexual selection the content of a song repertoire seems more relevant than its
size. In many birds close neighbors share a relevant percentage of their repertoire.
In many species local conditions favor the birth of dialects, and female usually
prefer males that are adopting such dialects. In some species, such as canaries
( Serinus canaria ), the presence of a fast trill of large bandwidth is very attractive for
females, which means that special syllables can be involved in the process of sexual
selection. In the case of the water pipit ( Anthus spinoletta ), males that present a
special “snarr” were mated more often than males with low scores (Rehsteiner
et al. 1998 ). Individuals that performed “snarr” had the highest body weight,
although other phenotypic characters (length of the eighth primary, tarsus length)
and age seem to not be related (Fig. 4.10 ). Finally, the “snarr” sounds seems to
increase reproductive success with important results in male-male competition.
It is well documented that body size of species is an indicator of frequency range
[ Regulus regulus (8.5-9.5 cm) and Turdus merula (23-29 cm) have a dominant
frequency of 8,000 and 4,000 Hz, respectively]. If this constraint is present also
within a species, females should distinguish larger from smaller males according to
their acoustic characters, and this character could be an honest signal in male
competition.
Also, timing of singing may be an indicator of individual quality. For instance, in
conditions of bad weather only high-quality males are singing. At dawn, there are
dominant males that sing early, which should have an energetic cost, but the
advantage is that a male sings a great deal when the female indulges in extra
copulation and when mate guarding is not possible. Individual singing early than
average times could represent an extra cost.