Birds protect their nests against predators in various ways. In addition to active defence, they can hide their nests or use the protection of other species breeding nearby that actively defend the nests. Studies evaluating these strategies simultaneously are rare, especially from areas unaltered by humans. Nest predation risks were studied in a wetland bird community at Lake Baikal, Russia. The community contained several species actively defending their nests, although most were “passive defenders”. Such tactics as active defence, concealed nesting, neighbourhood nesting and coloniality were tested for their effects on predation risk. The main predators
were birds, particularly carrion crows (Corvus corone). Analysis of 193 nests using multimodel inference based on Akaike’s information criterion
suggests the most successful tactic was active nest defence, although most birds applying this tactic build open (uncovered) nests. Passive defenders effectively reduced this risk by nest concealment and/or breeding near active defenders. Opposing patterns were found for active versus passive defenders near the most successful breeder but also a potential nest predator, the Mongolian gull (Larus mongolicus). Conservation implications emphasize support for large aggregations of active nest defenders, vegetation cover providing good nest shelter, and sufficient area of interior habitat reducing edge effects.
Variation in nest survival rates is often ascribed to differences in predator communities. Because corvids are the dominant nest predators in many landscapes with fragmented woodland, their absence may have effect on both the overall nest success and its relationship to habitat features. Nest success of Sylvia atricapilla was examined in two habitats in agricultural landscape of SW Slovakia, where corvids were rare/absent. The daily nest survival rate (126 nests) was 0.977 (95% CI: 0.966–0.984) and 0.966 (0.948–0.977) for the egg and nestling stage, respectively, yielding a nest success of 0.52 (0.37–0.64) over a 24-day period. These values are higher than in comparable studies from central Europe, although predation was still the leading cause of nesting failure (more or equal to 71% of 48 failed nests). Correlational evidence suggests link between local absence of corvids and the relatively high nest survival, which was only weakly affected by nest site and habitat characteristics. Nest survival was not detectably higher in forest fragment than in windbreaks and did not increase with distance from forest-field edge or with vegetation concealment. We conclude that both the habitat features and composition of local predator community should be considered when explaining patterns in nest survival rate.