The census and distribution of winteringwoodpigeons Columba palumbus in theIberian peninsula

Throughout the 1997-1998, 1998-1999 and 1999-2000 seasons, Woodpigeon population censuseswere carried out in their traditional Iberian wintering area, which comprises the southwesternquadrant of the Peninsula. The method applied was the direct counting of flocks incommunal roosts, of which 210 have been checked so far. Four counts were carried out perseason in November, December, January and February. As an average, 95% of the roosts werecounted simultaneously. Between 140 and 230 collaborators participated in each one of thecensuses. These collaborators were mainly wardens from the Spanish autonomous regions andthe Portuguese Government. Quantitative data suggests that the wintering population in thestudy area would total about 2.5-3 million birds, not including inter-yearly oscillations associatedwith reproductive success in the breeding areas. Their gregariousness remained relativelyconstant between November and January, 40-70% of the birds being counted in roostsof more than 400 000 individuals (1-2% of the number of roosts). Numbers were stable in thisperiod, in spite of some inter-monthly differences attributed to difficulties in obtaining fullcover. However, February offered a variable pattern. This phenomenon shows that dates ofstart of the spring migration must vary from year to year. The distribution of these contingentswas not homogeneous within the study area, a massive presence occurring in Portugal andExtremadura-Toledo alternately. The evaluation of acorn production in Iberian dehesas andmontados (pastureland) during 1999 provided interesting points for interpretation. For example,the low availability of food in cork tree woods during that winter explained the absenceof 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 capacityof the dehesa suggests that the analysis of this factor could allow predictions of the spatialand seasonal distribution of the population.

Bea, A., Beitia, R. and Fernandez, J. M. 2003., Ornis Hung. 12-13: 157-167.