Applications - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 263

food remain unaltered. This aspect has not been considered until the present, but
soundscape ecology could in perspective operate in this promising sector by
adopting bioacoustics procedures to evaluate the effects on the acoustic broadcast-
ing of species and the population dynamics.
Chemical pollution is a further consequence of human-based degrading pro-
cesses that can affect the acoustic repertoire of species. It has been demonstrated
that some birds reduce their repertoire when living in a strongly polluted area.
Gorissen et al. ( 2005 ) reported that the singing repertoire of birds living in a site
very polluted by heavy metals was significantly smaller and the birds emitted less
song than singers 4 km distant from the polluted area. Alteration of singing
behavior is a powerful indicator of environmental stress at the population level.
In a population of starlings ( Sturnus vulgaris ) living close to 20 sewage treat-
ment plants in the southwest UK, Markman et al. ( 2008 ) observed changes in their
acoustic behavior as a consequence of ingestion of earthworms highly
contaminated by synthetic and natural estrogens. In fact, these birds were singing
longer and performing a more complex song compared with control males. This
change was observed to be a major attraction for females, although in these males
an increase of immune function was experimentally confirmed. It was observed also
that the key brain area that controls the male song complexity is significantly larger
in the contaminated subjects. We can conclude that these animals are exposed to
pollution that reduces their health but that paradoxically these animals are more
attractive for females, changing the significance of the “honest signal” attributed by
several observations and experiments to the song function. This trait, modified by
altered physiology caused by environmental pollution, distorts sexual selection,
producing long-term negative effects in the population.
Hunting activity has direct numerical effects on populations of wildlife but other
aspects have to be considered. For instance, the rule to remove the older individuals
from one population, justified by the model that the older individual is at the end of
the life cycle and that young individuals have more possibilities to recruit is only in
part confirmed by evidence. Often the older exemplars have in their memory all the
experience accumulated and their removal reduces the chance for a group to better
survive without the use of this experience. For example, family groups of elephants
are guided by old matriarchs that have the capacity to discriminate between several
other families. The personal knowledge of the other individuals encountered during
the year is important for social cohesion, territory delimitation, and social
exchanges for all. Experiments conducted by McComb et al. ( 2001 ) on the vocal
recognition of different individuals have verified this hypothesis. Families with
older matriarchs were able to better discriminate familiar and unfamiliar females
when experimentally submitted to the playback of different groups.
In Gunnison's prairie dogs ( Cynomys gunnisoni ), a species distributed across the
southwestern United States, Slobodchikoff et al. ( 1998 ) have found a change in
alarm repertoire (local dialects) with changes in syllable length, number of
syllables, and length of calls. In this species the alarm calls vary according to
environmental conditions and the type of predators. Variations have been found