Survival chances of ground nests in three different habitats in Krka National Park (Croatia)

Abstract

Background and Purpose: Diverse Mediterranean wetlands sustain a high diversity of breeding birds. Breeding success of birds nesting on protected wetlands along river Krka is also influenced by predators. The aim of our study was to explore effects of predator pressures on ground nests of strictly protected birds using artificial nest located along environmental gradient.

Materials and Methods: In May 2004 in locality Čulišićke bare, by placing out three batches of 25 artificially constructed ground nests in three different habitats: reed bed, marsh and meadow. The nests contained three chicken (real) eggs for the evaluation of nest predation rates, and plasticine (artificial) eggs for predator identification from tooth and bill imprints.

Results and Conclusions: The number of nests depredated during one week was highest in wetland habitats: 52% was depredated in the marsh and 32% in the reed bed. However, a much lower damage rate (16%) was experienced in the meadow. The daily survival rate of nests did not differ significantly between the reed bed (0.95) and the marsh (0.91). However, the daily survival rates of nests in the meadow (0.98) was significantly higher (z = 2.49 P = 0.01) than in the marsh, bat no difference was found with comparing with the reed bed. Predators were difficult to determine because plasticine eggs usually disappeared from the nests in the reed bed. In the marsh and the meadow, primary predators were smaller birds, whereas small mammals were also important in the marsh. Nests in which predators succeeded in breaking at least one egg were later destroyed most by Hooded Crows (Corvus cornix). To apply these results for bird protection, the breeding success of certain threatened bird species should be monitored for a longer period.