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)

Abstract

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 <em>Picus canus</em> and <em>Picoides tridactylus</em> in Friuli-Venezia Giulia (NE Italy). <em>P. canus</em> resulted as being more responsive than <em>P. tridactylus</em> 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 <em>P. canus</em> was song, heard in 57.89% of the points, while for <em>P. tridactylus</em>, 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. <em>P. canus i</em>n Friuli-Venezia Giulia was found from altitudes close to the sea level up to the treeline (range 0-2000 m a.s.l.), while <em>P. tridactylus</em> 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.<em> P. tridactylus</em> 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<em> P. canus</em> and 0.16-0.40 territories/100 ha for <em>P. tridactylus.</em> 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<em> P. canus</em> compared to the beginning of the century, and just over 60% for the other species. Finally, some aspects concerning conservation-related problems are reported.