Table 1.

Average levels of background sounds and bird choruses in dB(Z) (unweighted Sound-Pressure-Level) and dB(A) (A-weighted LAeq values).

Stimulus	Ambient sound	Ambient sound min	Ambient sound max	Aircraft noise	Aircraft noise min	Aircraft noise max	Chorus: 1 individual	Chorus: 5 individuals from the same species	Chorus: 5 individuals from different species
dB (Z)	38	24	36	44	29	50	27	44	37
dB (A)	23	18	21	30	19	40	28	40	38

“min” and “max” values correspond respectively to the lowest and highest average value of each class of background sound. Background dB(Z) values are higher than dB(A) values because they show more energy at low audio frequencies [0–1 kHz]. Conversely, chorus dB(Z) values are lower than dB(A) values because they show more energy at high audio frequencies [1–10 kHz].