Abstract:

I investigated the numerical response of the Common Buzzard to variations in density of small mammals. The study was carried out at the Hortobágy region in 2000-2001. Du­ring nest visiting periods clutch size, number of hatched and fledged young were recorded. Population of small mammals were also monitored by live-trapping. Effect of weather on the survival of overwintering rodents was also investigated. There was significant difference in clutch size between 2000 and 2001 (means 2.3 and 3.1). It can be explained by the remarkable differences in abundance of small mammal populations between the two years. The density of rodents was very low (9 specimen/ha) in 2000. During 2001 the amount of small mammals has increased more than eightfold (76 specimen/ha). In February and March, 2000 there were 4 short mild periods alternating with 4 freezing periods, when distribution of significant precipitation (6-8 mm rainfall in each) coincided with the mild periods. Thus the overwintering population almost extincted from the area because the tunnel complexes of voles are repeatedly flooded and huge part of the animals died, resulting very low density during the breeding season. In 2001 there was no such alternating periods, mild weather started 3 weeks ear­lier, thus voles overwintered successfully and their numbers increased rapidly producing a peak during the bree­ding season.