Ornis Hungarica. vol.12-13. (2003) p.157-169.
The census and distribution of wintering woodpigeons columba palumbus in the Iberian peninsula
Throughout the 1997-1998, 1998-1999 and 1999-2000 seasons, Woodpigeon population censuses were carried out in their traditional Iberian wintering area, which comprises the southwestern quadrant of the Peninsula. The method applied was the direct counting of flocks in communal roosts, of which 210 have been checked so far. Four counts were carried out per season in November, December, January and February. As an average, 95% of the roosts were counted simultaneously. Between 140 and 230 collaborators participated in each one of the censuses. These collaborators were mainly wardens from the Spanish autonomous regions and the Portuguese Government. Quantitative data suggests that the wintering population in the study area would total about 2.5-3 million birds, not including inter-yearly oscillations associated with reproductive success in the breeding areas. Their gregariousness remained relatively constant between November and January, 40-70% of the birds being counted in roosts of more than 400 000 individuals (1-2% of the number of roosts). Numbers were stable in this period, in spite of some inter-monthly differences attributed to difficulties in obtaining full cover. However, February offered a variable pattern. This phenomenon shows that dates of start of the spring migration must vary from year to year. The distribution of these contingents was not homogeneous within the study area, a massive presence occurring in Portugal and Extremadura-Toledo alternately. The evaluation of acorn production in Iberian dehesas and montados (pastureland) during 1999 provided interesting points for interpretation. For example, the low availability of food in cork tree woods during that winter explained the absence of birds in the Portuguese districts, and may have stimulated the start of migratory movements. The seemingly direct response shown by wintering Woodpigeons toward the nutritional capacity of the dehesa suggests that the analysis of this factor could allow predictions of the spatial and seasonal distribution of the population.