Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 69

of benefit such as antipredator behavior of consociated species, use of information
about the quality of the shared habitat, abundance of social stimuli that accelerate
and improve the breeding cycle, and increase in efficiency to a communal defense
from predators. In particular, many species of birds have the capacity to utilize the
acoustic information of other birds.
Heterospecific attraction may be possible if the resources are honestly signaled.
Resident species have more time and energy to explore the local resource and to
cope better than migratory birds with local environmental peculiarities.
Residents have already avoided the risky portion of a suitable habitat or have
been eliminated by a predator, so the presence of residents in a specific area has
high probability to be a signal of habitat safety.
If competition is present between residents and nonresidents, the visitors will try
to avoid the habitat patches already occupied by residents. In contrast, if there is no
competition between species, this will favor the selection by visitors of the patch
already occupied and tested from the aspect of the resources by the residents.
Observational and experimental evidence is in accord to recognize that the
heterospecific attraction is not an artifact but a diffuse phenomenon, especially in
areas in which resident and migratory species have common habitat. For instance,
there is experimental evidence that titmice density attracts other passerines after a
change in local density produced artificially by providing food to titmice in winter
and nest boxes during the breeding season (M¨nkk¨nen and Forsman 2002 ).
Further experimental evidence by Doutrelant et al. ( 2000 ) has proved that
interspecific competition may have an important role in the macrogeographic
variation of birdsong. In the blue tit ( Cyanistes caeruleus ) there are variations in
song repertoire according to geography, so there are populations that have a trill and
other populations without the trill. This characteristic is correlated with the breed-
ing density of the great tit ( Parus major ) and not with other possible environmental
factors such as vegetation structure or blue tit density. These authors tested the
hypothesis that the trill of the blue tit was representing a character shift to reduce
competitive interactions with the dominant great tit. Experiments conducted in
Corsica, mainland France, and Denmark consisted of presenting a blue tit trill to
the great tit and also untrilled song and great tit song. The great tit responded
somewhat well to male great tit song and to blue tit untrilled song; its reply was
weaker to trilled blue tit song. This observation confirms how the modification of a
character can reduce interspecific competition via an acoustic communication
change.
Conspecific attraction plays an important role in habitat selection and on repro-
ductive performance (habitat copying). The hypothesis that birds aggregate
according to social cues more than environmental cues is consistent with the results
obtained by Redmond et al. ( 2009 ). The eastern kingbird ( Tyrannus tyrannus ) has
been observed by these authors to occupy only a part of the suitable habitat during
the breeding season at Malheur National Wildlife Refuge in southeastern Oregon.
Kingbirds have a tendency to settle where there is a high conspecific density
(Fig. 4.2 ). It is true also that individuals settle in the areas where in the past year
more fledglings have been produced (habitat copying).