Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 90

4.14 Acoustic Partitioning in Birds and Frogs

The involuntary overlap of heterospecific acoustic performances reduces the
efficiency of the signals. To reduce interspecific acoustic interference, species can
adopt two main strategies at least: choice of time and space for singing, or evolving
different typology of songs.
Often a signal is produced in a noisy environment, especially in environments
with a high diversity of vocal species, and detectability and discriminability are the
two properties that a signal should conserve to be useful, reducing the interference
with irrelevant signals.
Considering that the environmental noise rarely is continuous, as during a heavy
rain or close to the sea during a tempest, or near a waterfall, there are possible gaps
in which a signaler can place its signal, reducing overlap and interference with other
signals.
This process is called acoustic partitioning and consists of changing the time at
which to start an acoustic performance in the presence of other concurrent singers.
During a dawn chorus many species and individuals sing with a temporal
turnover to minimize the interference effect.
Time partitioning was observed by Luther ( 2008 ): among 106 species of birds
that sang at dawn in Alta Forest, Mato Grosso, Brazil, 34 species sang in a 30-min
or 1-h time. Of these species, 2 sang within 30 min of sunrise: the white-browed
antbird ( Myrmoborus leucophrys ) and warbling antbird ( Hypocnemis cantator
striata ). Two other species, the chestnut-backed antshrike ( Thamnophilus palliatus
palliatus ) and the black-faced antthrush ( Formicarius analis ), sang more frequently
during 1-2 h after sunrise (Fig. 4.11 ). Playback experiments were conducted with
these 4 species, receiving replies from each species during the typical song time.
Response outside the typical song period was observed but was less intense and less
immediate. This experiment has proved that some species use temporal partitioning
to reduce acoustic interference.
This author has confirmed in another location a clear dispersion of the song of
82 sedentary species that sang at dawn (Luther 2009 ). In fact, song of congener and
family members was more dispersed than the song of species selected at random.
This research has demonstrated that species present in the same place and time
partition signal space, a phenomenon observed also by Malavasi and Farina ( 2013 )
in dusk choruses of birds in a Mediterranean woodland.
In a neotropical highland-frog community, L¨ddecke et al. ( 2000 ) have found
species partitioning the acoustic space although such a community is composed of
only five species ( Hyla labialis , Eleutherodactylus elegans , Eleutherodactylus
ebogotensis , Eleutherodactylus enervicus , and Colostethus subunctatus ) that have
distinct ecological traits. These species have distinct call patterns and are calling at
different periods of the day. Despite the low frog diversity and the use of land sites
from which to call, only one species calls in ponds ( Hyla labialis ); the other
are calling in different types of plants and at different heights from the soil, so
acoustic partitioning remains an important behavioral trait for reliable vocal

communication.