Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 68

stronger predatory response to the calling song of the two species of Tettigonia, and
M. myotis showed a higher predatory response to the beetle rustling and to one
tettigoniid species. This experiment has demonstrated eavesdropping on prey
communication signals and also sensory partitioning between the two sympatric
bat species.
4.4 Echolocation: A Special Case of Communication
Echolocation is a winner strategy in bats. The efficiency of this sonic mechanism
depends by the distance at which a bat can intercept a prey by isolating background
and vegetation effects. For this it is important to investigate the distance at which
bats can detect a prey and separate the echoes from rocks, water surfaces, trees, and
meadows. A main topic that remains to be explained is if bat echolocation distance
of prey depends on the distance of the prey from the background. Two different
theories have tried to explain this matter: first, bats produce impulses that are long
enough that there is time for returning echoes before the emission of a successive
pulse; and in the second hypothesis, bats alternate between different call types and
thus ambiguous identification is strongly reduced. Frequency of calls and atmo-
spheric condition are the limiting factors over which audible echoes are reflected
from a target to an echolocating bat. The frequency is a very important component
of echolocation: low-frequency signals are used for long-range echolocation,
and high frequencies are used for short-range echolocation. Bats that use low
frequencies and a high source level (SL) forage in forested areas, but bats that use
a high-frequency range and lower SL search their prey in open areas. Bats living in
tropical forests where humidity is very high that are foraging inside dense vegetation
have a high-frequency signal and very low SL (Stilz and Schnitzler 2012 ).
4.5 Heterospecific and Conspecific Attraction
It has been observed that some species are attracted by a portion of habitat already
occupied by other species. This phenomenon was been first coined by M¨nkk¨nen
et al. ( 1990 ) as “heterospecific attraction.” For instance, migratory birds have been
observed to be attracted by resident species that probably have more information
about available resources. Breeding habitat selection is a fundamental step in the
life of a species, and if a species has a migratory habit good knowledge of the more
useful habitat is quite reduced. For this reason, resident species can operate as
involuntary informers for such species.
Population density, habitat structure, floristic, acoustic cues, predatory pressure,
and conspecific and heterospecific contacts are some of the environmental variables
that concur in breeding habitat selection. Some species have been proved to prefer
to settle close to other species in a way that is reasonable to think there is some type