Responsiveness to acoustic stimulation, distribution and habitat preferences of the Grey-headed Woodpecker, Picus canus, and the Three-toed Woodpecker, Picoides tridactylus, in Friuli-Venezia Giulia (North-eastern Italy)

The study was carried out from 2003 to 2011 with the aim of determining the responsiveness to acoustic stimulation, the distribution and the habitat preferences of Picus canus and Picoides tridactylus in Friuli-Venezia Giulia (NE Italy). P. canus resulted as being more responsive than P. tridactylus to conspecifics stimulation, responding in 13.23% of the points where a stimulus was emitted, against 7.65% of the other species. In both taxa, when there was a response, it was predominantly by the male birds. The most frequent type of response in P. canus was song, heard in 57.89% of the points, while for P. tridactylus, it was drumming, which was heard in 65.38% of the points. For both species (especially for P. tridactylus), a tendency was recorded to expand the range and to occupy new areas within the known range. P. canus in Friuli-Venezia Giulia was found from altitudes close to the sea level up to the treeline (range 0-2000 m a.s.l.), while P. tridactylus was found in montane and subalpine woodlands (range 800- 2000 m a.s.l.). The observations of P. canus were obtained at a mean altitude of 977 m a.s.l. (± 402 SD), located in the altitudinal belt dominated by Fagus sylvatica L., which is present in more than half of the woodlands in which the woodpecker was found. P. tridactylus was discovered at a mean altitude of 1424 m a.s.l. (± 246 SD), located in the altitudinal belt dominated by Picea abies (L.) H. Karst., which is present in almost 90% of the woodlands in which this species was found. In some areas, densities of 0.67-2.26 territories/100 ha were obtained for P. canus and 0.16-0.40 territories/100 ha for P. tridactylus. In Friuli-Venezia Giulia, a population of 320-390 pairs of P. canus and 45-60 pairs of P. tridactylus has been estimated, with an approximate 15% increase of P. canus compared to the beginning of the century, and just over 60% for the other species. Finally, some aspects concerning conservation-related problems are reported.