Abstract: Monitoring wolves (Canis lupus) is a difficult and often expensive task due to high mobility,pack dynamic, shyness and nocturnal activity of this species. Wolves communicate acoustically trough howling, within pack and with packs of the neighbourhood. A wolf howl is a low frequency vocalization that can be transmitted over long distances and thus be used
for monitoring tasks. Animated howling survey is a current method to monitor wolves indifferent areas all over the world. Animated howling, however, may be invasive to residential wolf packs and could create possible negative reactions from local human population. Here we show that it is possible to detect wolves by recording spontaneous howling events. We measured the sound pressure level of wolf howls on captive individuals and we further found that simulated howling may be recorded and clearly identified up to a distance of 3 km. We finally conducted non-invasive acoustic detection of wolves in a free ranging population. The use of passive sound recorders may provide a powerful non-invasive tool for future wolf monitoring and thus help to established sustainable management plans for this species.

Abstract: Wolf choruses ( Canis lupus ) are complex, multicomponent signals, composed by a series of different vocalizations emitted by a pack. Although howls, the main component, have been highly studied, poor attention has been drawn upon the other vocalizations of the chorus. In this study, we investigate the structure of the chorus by means of the analysis and the quantification of the different components, taking advantage both of the digital sound recording and analysis, and of the modern statistical methodologies. We provide for the first time a detailed, objective description of the types of call emitted during the wolf howlings, combining spectrographic examinations, spectral analyses and automated classifications, with the aim to identify different types of call. Our results show that wolf choruses have a rich, complex structure, that reveals six other types of call, to be added to those howls already described in literature. Wolf choruses are typically composed by other three different types of calls: the bark, i.e. relatively long calls characterized by low frequencies and the presence of harsh components (deterministic chaos); the whimper, characterized by a harmonic structure and a very short duration; and the growl, a call with a noisy structure, low frequencies but relative long duration. Although further investigations are necessary to understand the meaning of the different calls, this research provides a basis for those studies that aim to compare wolves and other canids vocal behaviour.