The Wren (Troglodytes troglodytes) is renowned among Ornithologists for the variable nature of its loud song. The main characteristic of a local population’s dialect is that clearly defined and distinguished song types are unique to individuals in one population, and therefore are not found in adjacent populations. This results in a mosaic of distribution of song types, often with sharply defined boundaries between different dialect areas (Catchpole and Rowell 1993).
Sounds become degraded by long-distance propagation through natural habitats, especially woodland. Vegetation and atmospheric turbulence impose physical constraints to sound signals such as amplitude and reverberation. In response to these degradations, birds have developed adaptations related to sound structure during their evolutionary history. Wrens seem to have a coding process mis-adapted to this way of life. It has a very high-pitched song (mean frequency = 5500 Hz), which is very susceptible to degradation. Furthermore, the Wren lives in the low layer of vegetation, where the vegetation density is great. It appears that the wren is sensitive to this degradation since the territorial reaction is less intense with the degraded song than with the un-degraded one. However, the degraded song is still considered by the receiver as a specific territorial aggressive signal. This differential response suggests that the male wren can use the degradation characteristics of the signal to adapt its territorial reaction. Indeed, in response to this stimulus, the receiver wren chooses a higher song post. By so doing, the bird improves both the propagation distance of the emitted song and the receiver’s ability to hear the opponent’s song. This behavioural change may correspond to a communication strategy, counteracting the environmental constraints on sound propagation. Therefore, in response to sound degradation during long-range propagation, birds may have developed behavioural adaptations complementary to the various adaptations concerning song structure and coding-decoding processes (Mathevon and Aubin 1997).
The territory of this highly territorial bird serves a variety of functions, including dispersal, pair-formation, safeguarding reproductive activities and providing a foraging area. There is a correlation between food supply, activities connected with the territory and the character of the pair-bond. Territoriality is considered to be basically concerned with reproduction and is regarded as an integrated set of activities in which vigor is the fundamental concept for territorial individuals (Armstrong 1956).
Reference List:
- Armstrong.A.E., (1956) Territory in the Wren (Troglodytes troglodytes). IBIS, 98, 430-437.
- Catchpole.K.C., & Rowell.A., (1993) Song Sharing and Local Dialects in a Population of the European Wren (Troglodytes troglodytes). Behavior, 125, 67-78.
- Mathevon.N., & Aubin.T., (1997) Reaction to conspecific degraded song by the wren (Troglodytes troglodytes): Territorial response and choice of song post. Behavioural Processes, 39, 77-84.
