The grey heron is an extensively studied and widely distributed colonial bird species in the Old World; however, relevant information on the role played by vocalisations during the life cycle of ...individuals is still lacking. This research aimed to deepen the available knowledge on the repertoire and vocal behaviour of adults during the breeding season, through a bioacoustic approach and choosing as study areas two heronries in different environmental contexts. Colonies were monitored 2 days a week each, for 9 weeks, from 8:00 am to 6:00 pm (360 hr of sampling). Results showed that adults use a wide range of call types, mainly related to courtship and the reproductive phase. Vocalisations are emitted especially by males and are a key element during mate attraction, nest building, in breeding events and in strengthening bonds within pairs. Most vocalisations are expressed in the first weeks of the breeding cycle, concurrently with the maximum number of courtship males, which exhibit most of the detected sound categories and emit calls with lower frequencies than females. Moreover, these vocalisations are expressed to a greater extent in the heronry characterized by an important forest component, where an almost entirely exclusive sound category was detected. In conclusion, the results suggest a possible correlation between vocal behaviour and female choice. The wide variety of sound signals and the high rate of calls produced by males during attraction and courtship displays, together with the acoustic characteristics of the signals, could provide honest estimates of the quality of emitters.
The Eurasian griffon vulture (Gyps fulvus) represents an exception among the European accipitrids, as it forms highly populated colonies. Although it has been the subject of many studies, social ...interactions and intraspecific communication are still relatively unexplored. Because of its social habits, we hypothesise that the sound language of the griffon vulture is far more complex than previously believed; the 'Social Intelligence Hypothesis' could in fact be relevant to this species. In this study, we took as a model the vulture population of the central Apennines (Italy), comparing the vocalisations recorded in three different locations: (i) supplementary feeding station; (ii) nesting and roosting cliffs far from anthropogenic disturbance; (iii) nesting and roosting cliffs close to settlements and roads. The results obtained by 80 monitoring hours and 20 recording hours show an articulated vocal repertoire, characterised by 12 sound categories associated with different age groups and possibly to very specific behavioural contexts. The vocal repertoire is also marked in some cases by nonlinear phenomena revealing different degrees of behavioural complexity related to the expression of emotional states and social interactions. The next steps will focus on individual recognition mechanisms and the interactions with other species sharing part of the same ecological niche.
