Comparative breeding ecology, nest survival, and agonistic behaviour between the Barred Warbler and the Red-backed Shrike

Abstract

The majority of studies have demonstrated that the Barred Warbler Sylvia nisoria (BW) and the Red-backed Shrike Lanius collurio (RBS), where they occur sympatrically in central Europe, inhabit similar niches and are not averse to nesting in each other’s vicinity. The present work compares the reproductive parameters, nest survival, and behavioural interactions between these two ecologically similar species. The study was carried out in eastern Poland in two types of habitat: a river valley and farmland. Inter-habitat analysis showed both species to have similar reproductive parameters, although nest survival of the RBS was greater in farmland than in the river valley. Interspecific comparison revealed that the BW built smaller nests, laid fewer and smaller eggs than the RBS, but the production of offspring was similar in both species. In comparison to the other populations from Europe, both the BW and RBS in eastern Poland experienced good breeding parameters, and this is likely to be related to the region's extensive agriculture management and abundant food resources. The main factor reducing breeding success in both species was the plundering of their broods by raptors. Analysis using the MARK program indicated that habitat parameters significantly affected brood survival in the RBS to a relatively constant extent throughout the season. While habitat factors were less decisive in BWs, the fate of this species’ broods was strongly dependent on the phase of the reproductive cycle, and its nests were least likely to survive in the middle of the breeding season. The level of aggression between the BW and RBS was low, as demonstrated by experiments with stuffed models; this was a factor in favour of their nesting in close proximity to one another.