Arboreal singing in a burrowing cricket,Anurogryllus arboreus

Summary

• 1. Anurogryllus arboreus males in north peninsular Florida sing at ground level or above the ground on the trunks of trees or on other vegetation. Their song is a continuous trill at 70–80 pulses/s and 5.0–5.5 kHz. Prevailing singing locations of individual males vary among and within denies (Fig. 2). Males of congeneric West Indian species sing only at ground level.

• 2. Females are flightless and climb plants only in response to male calls. Therefore the three-dimensional acoustic output of a male may be of less direct importance than the male'sbroadcast area — the area at ground level within which the intensity of his call exceeds the auditory threshold of the average female.

• 3. Assuming a threshold of 38 dB (SPL re 2 × 10⁻⁵N · m⁻²) we found that males calling 1 m above the ground had broadcast areas averaging 14 times the broadcast areas of males calling at ground level (119 vs. 1,642 m²) (Fig. 4A-D, Table 1).

• 4. In terms of broadcast area, the optimal height for singing is influenced by spreading loss at greater heights, by attenuation due to ground cover and low vegetation, and by acoustical shadows due to rough terrain.

• 5. On vertical surfaces, such as tree trunks, crickets more often (27∶1) sing facing right or left than up or down (Fig. 3) making the broadcast areas asymmetrical (Fig. 4B-D).

• 6. When crickets singing on vertical surfaces deviate more than 22.5° from the horizontal, they generally (7∶1) angle downward (Fig. 3). Facing downward apparently has no acoustical advantage over facing upward since sound levels behind a cricket calling on the ground are at least as intense as those ahead (Fig. 4E).