Predictions From the Ranging Hypothesis for the Evolution of Long Distance Signals in Birds

Abstract

The Ranging Hypothesis (RH) (MORTON, 1982) proposed a form of distance assessment (ranging) based upon perception of signal degradation using memorized signals as a yardstick to distance. The predictions of the RH include distance assessment mechanisms, DAMs; it is proposed that these have opened a new evolutionary process illustrated by the complicated songs and singing behaviour in the oscine passerines ("songbirds"). The RH identifies sources of selection favouring learning, multiple or single song types, song structural complexity not accounted for by species isolating mechanism ideas, and emphasizes the ecological basis for the evolution of long distance communication. New importance is given to the acoustic physical structure of songs. The RH encompasses and contrasts song evolution in warm climate regions with those in cold temperate climates. Three interrelated stages of long distance signal evolution are presented: detectability, threat, and disrupt. A singer/listener role dichotomy in selective pressures is described and the results discussed. Listeners developed distance assessment mechanisms (DAMs) resulting in an evolutionary arms race between listeners and singers. Singers developed methods to use DAMs to their best interest (threat and disrupt). Song learning in passerines developed in response to this arms race to enhance disruption, a situation most prevalent in cold temperate zone regions. The acoustic determinants of effective song distance are described and discussed in relation to the evolution of signal structures. Finally, the RH is discussed in relation to some previous hypotheses on song function and evolution.

Spectral characteristics of intense mew calls in cat species of the genus Felis (Mammalia: Carnivora: Felidae)

“…This habitat classification (dense vs. open) (Table 4) is coarse with regard to sound propagation conditions. Therefore, the AAH can only be addressed here in a more general manner with regard to signal attenuation (decrease of amplitude), not degradation [changes in temporal patterning of the signal's structure (Morton 1986)], when traveling through the species' habitat type. Degradation is also highly unlikely to play a role in long-distance acoustic communication in the cat taxa studied.…”

An Evolutionary View of the Origins and Functions of Avian Vocal Communication.

“…The bird perceives the apparent distance to the vocalizer because degradation increases with distance (Morton 1986). Ranging is performed by listeners it is assessment, and, as such, has profound effects upon managers and the evolution of their vocalizing.…”

Chickadee Song Structure is Individually Distinctive Over Long Broadcast Distances

“…Song structure, therefore, is generally more vulnerable to environmental degradation than other potential song indicators of male social rank or identity such as repertoire, repertoire size or song output measures. The relationship between the amount of degradation in a signal and its propagation distance is not always predictable (Dabelsteen et al, 1993), but it is profound enough to permit many birds to use it for distinguishing near from distant songs (Morton, 1986;McGregor & Krebs, 1984;McGregor, 1991;Naguib, 1995Naguib, , 1997. Chickadees appear similarly capable of attending to structural degradation caused by distance propagation through the environment (Phillmore et al, 1998; but see Fotheringham & Ratcliffe, 1995).…”