Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)

Fenyősi, László: Studies of avian communities along river Drava, between 2000-2004 (Aves) - Madárközösségek vizsgálata a Dráva somogyi szakasza mentén, 2001-2004-ben

128 NATURA SOMOGYIENSIS Fig. 5.: Changes in Riparia riparia population between Drava river kilometres 199-133 trend of population size changes was found to be decreasing. The distribution of colonies according to nest hollow numbers is shown in Fig. 6. From this figure it appears that the proportion of colonies with less than 200 nest hollows is considerably higher than the combined proportion of larger colonies. However, in 2003-2004 the distribution of colonies with diffeent sizes is much more balanced. In each of the years, the largest colony formed near Heresznye (188 river km and 184-185 river km), with the largest colonies numbering 950-720-348-666-600 pairs, respectively, in successive study years. For a more exact knowledge of Riparia riparia populations in the region, in addition to surveying the sample area, from 2001 we have also made censuses in three extra areas: in the mostly Croatian Drava section between 236-199 river kms, in the Viktorpuszta sand pit in the vicinity of the town Bares, and at the waste-heap embankment of the Csíkos pit lake at Bélavár. The results are presented in Table 9. Fig. 6.: The distribution of nesting colonies, based on nest hollow numbers, between Drava river kilometres 199-133