Lee Koren and Eli Geffen (2011): Individual identity is communicated through
multiple pathways in male rock hyrax (Procavia capensis) songs. Behav. Ecol.
Sociobiol. 65 (4), 675-684.
Abstract: Communicating individual identity is essential for stable social
systems. It is assumed that there are benefits for both senders and
receivers to provide and discriminate identity cues. In this study, we
investigate the possible routes senders use to acoustically broadcast their
individual identity. Using discriminant function analysis of temporal and
spectral acoustic measurements and analysis of song-element order, we
explore the means male rock hyrax (Procavia capensis) singers utilize
vocalization to express individual identity. Despite the fact that males use
only three song elements, the pattern of acoustic characteristics, their
temporal and frequency attributes vary according to the identity of singer.
We show that in hyrax, individuality is expressed by highly variable,
complex signals that are not condition dependent and are stable over years
in singers that did not alter their spatial position. We also show that
individuality signals are not linked to relatedness or to geographic
location. The ability to discriminate individuals from vocal signatures
needs to be further tested using controlled playback experiments.
For reprints please contact Lee Koren (email:
Maria Clara P. Amorim, José Miguel Simões, Vitor C. Almada & Paulo J.
Fonseca (2011): Stereotypy and variation of the mating call in the
Lusitanian toadfish, Halobatrachus didactylus. Behav. Ecol. Sociobiol. 65
Abstract: Signal attributes should show different degrees of variability
depending on the information to be conveyed. Species identity is usually
associated with stereotyped features of a signal, whereas other types of
information such as individual quality and motivation are associated with
signal plasticity. Lusitanian toadfish males form aggregations during the
breeding season and emit a tonal advertisement call (the boatwhistle) to
attract mates to their nests. We test the hypothesis that the boatwhistle
can convey information both on individual identity and motivation by
checking how signal parameters vary with time. We study how the physical
(tide level) and social (calling alone or in a chorus) environments and male
calling rate affect this advertisement signal and how all these external and
internal factors (environment, social and male motivation) blend to modulate
the Lusitanian toadfish?s advertisement call. Boatwhistles of each male were
very stereotyped in short periods of time (minutes), but intra-male signal
variability greatly increased in a longer time scale (days). Nevertheless,
significant differences among males could still be found even in a long time
scale. Pulse period was the acoustic feature that most contributed to
discriminate among males. Tide level and male calling rate modulated
boatwhistle characteristics, and there was a differential effect of tide on
call attributes depending on male calling rate. Social acoustic environment
only affected calling rate. These results suggest that inter-individual
differences in call characteristics and call plasticity may mediate both
male?male assessment and mate choice.
For reprints please contact Maria Clara Amorim (email:
Adrienne L. DuBois, Stephen Nowicki & William A. Searcy (2011):
Discrimination of vocal performance by male swamp sparrows. Behav. Ecol.
Sociobiol. 65 (4), 717-726.
Abstract: In aggressive communication, the interests of signalers and
receivers are directly opposed, presenting a challenge to the maintenance of
reliable signaling. Index signals, whose production is constrained by
physical ability, offer one solution to the reliable signaling problem.
Vocal performance, the ability to produce physically challenging songs, is
likely such a signal in swamp sparrows. Maximum vocal performance varies
between males and is correlated with aspects of quality. However, vocal
performance can be modulated in aggressive contexts by increasing the
frequency bandwidth and trill rate of songs. This study examines receiver
response to (1) differences in performance of the same song types by
different signalers and (2) individual modulation of performance between
contexts. Results demonstrate that male receivers show differential response
to between-male differences in song type performance, but do not show
differential response to the smaller scale modulations of performance
produced by individuals singing the same song type at different times. This
pattern suggests that vocal performance cannot be effectively cheated and
may therefore serve as a good example of an index signal.
For reprints please contact Adrienne DuBois (email:
Dr. Sonja Amoser