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

FENYŐSI С.: STUDIES OF AVIAN COMMUNITIES 125 Fig. 3.: The Drava section between river kilometres 199-180 Population survey of Sterna species Populations of Sterna species settling on gravel shoals were surveyed in the Drava section between Ortilos (236 river km) and Bolhó (180 river km) in 2000-2004 (there are no gravel shoals in the Drava section below Bolhó that are suitable for stern nesting, therefore new colonies are not expected to form). Between 2000-2004 there were 2-3 nest colonies annually in the Drava section between Ortilos (236 river km) and Bolhó (180 river km), with 5-14 pairs of Sterna albifrons, and 50-90 pairs of Sterna hirundo nesting there (Table 5.). Unfortunately, nestings proceeded at a very low success rate in the studied period, due to late flood waves. According to earlier experience, water levels above 200 cm measured on the Bares fluviometer are always with critical effect on nest colonies, these flood waves necessarily destroying the clutches. Daily water levels of the Drava, measured in Bares in May-July 2004 are shown in Fig. 4. Table 5.: Stern colonies in 2000-2004, between 236-180 Drava river kilometres Year Drava, 230-229 river km Drava, 218 river km Drava, 190-191 river km Year S. albifrons S. hirundo S. albifrons S. hirundo S. albifrons S. hirundo 2000 min. 8 pairs min. 36 pairs 0 0 min. 6 pairs min. 20 pairs 2001 min. 2 pairs min. 45 pairs 0 0 min. 8 pairs min. 45 pairs 2002 0 0 0 0 min. 5 pairs min. 50 pairs 2003 0 0 min. 2 pairs min. 15 pairs min. 6 pairs min. 40 pairs 2004 min. 1 pairs min. 25 pairs min. 2 pairs min. 11 pairs min. 4 pairs min. 40 pairs