Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 91

Fig. 4.11 Amount of song activity during morning hours of warbling antbird ( Hypocnemis
cantator striata ), white-browed antbird ( Myrmoborus leucophrys ), black-faced antthrush
( Formicarius analis ), and chestnut-backed antshrike ( Thamnophilus palliatus palliatus)
(Reproduced with permission from Luther 2008 )
4.15 Communication on Steep Soils
Generally acoustic communication is observed and studied in flat areas or on gentle
slopes, and when moving along the steep sides of a mountain range the topographic
constraint immediately appears that modifies direction and intensity of the sonic
ambient. In fact, the sonic ambient is strongly influenced by the steepness and by a
nonuniform distribution of the acoustics waves that are not easily perceived. So,
steepness not only affects abundance, distribution, and movement of organisms but
also the communication of vocal animals. Birds that sing upslope have a greater far
distribution of sonic energy, and in contrast birds singing downslope have a very
narrow distribution of sound (Fig. 4.12 ) Hunter ( 1989 ) reports an interesting
observation made on 40 birds, including 21 passerine birds, during their singing
behavior along a steep slope in the Kulu and Ravi valleys of the Western
Himalayas, India. Of 48 observations 37 were upslope, 9 parallel to the slope,
and only 2 downslope, confirming the strong orientation of birds on steep slopes.
However, factors such as steepness of the slopes, tree height, and perch height were
not significantly correlated with body orientation of the birds during their singing
performance. Further research would clarify the effect of topography on the com-
munication of birds and on their distribution in a landscape.