The Ecology of Avian Acoustical Signals
85
Distance= 200 m, receiver height
0.1 m
10
-5
(l)
<::>
c
0
-20
-m
::::>
c
(j)
:::::;
<(
-35
0.3
-50
0
2
4
6
8
10
Frequency (kHz)
Fig. 1. Model calculations for frequency-dependent excess attenuation caused by ground
effects. Distance between sender and receiver is 200 m, and receiver height is 0.1 m.
Different curves apply to different sound source heights given in m (0.3, 6, 12, 24, 48).
Based on the Delany-Bazley ground model with local reaction assumption and ground
impedance 50 kPa (average forest floor) with a 0.1 m porous layer (see Sutherland and
Daigle 1997). These particular calculations are representative for the habitat and behavior
of thrushes, Turdus, that feed on the ground (receiver) and sing at various heights (6 - 48
m), or formicariid antbirds that receive and sing (0.3 m) close to the ground in a forest
Good locatability is required for mate attraction, long-range communication
between social partners, and possibly for attracting members of mixed-species
flocks and mobbing gangs. It should be low, however, for alarm calls that induce
fleeing or hiding.