Wolves Canis lupus use long distance vocalisations (howling) for territory maintenance and group consolidation (Harrington, Mech 1979; Nikolskij, Frommolt 1989). The acoustic feature of long distance signals should be designed for best transmission in the habitat (Morton 1975). Additionally, animals should specialise in calling during hours when transmission is best. Nocturnal temperature inversions should increase communication range (Larom et al. 1997). Measurements on the acoustic features of chorus howling were obtained from three captive grey wolf packs. The choruses consist of two components: a part with nearly no frequency modulations (A-part) and a part with deep frequency modulations (B-part). Sound energy in the A-part is concentrated around 400 Hz, whereas in the B-part maximum amplitudes are in the region between 800 until 1200 Hz. In general the B-part has higher amplitudes. It is proposed that the B-part would be more effective in sound propagation in respect to environmental noise and excess attenuation. The diurnal distribution of howling was compared for wolf packs in different habitats and in captivity. Wild wolves howl primarily during night-time whereas captive animals vocalise almost during daytime. These findings indicate that the diurnal changes in vocal activity are primarily caused by ecological factors other than the sound transmission conditions.