Fitness-related parameters improve presence-only distribution modelling for conservation practice: The case of the red-backed shrike

The red-backed shrike (Lanius collurio L.) is a bird living in human-altered agricultural areas that are managed by extensive farming techniques. This passerine species has declined significantly in Western Europe over the last 30–40 years. The development of efficient species-specific conservation strategies relies on fine-grained information about the ecological resources and environmental conditions that constitute its reproductive habitat in this agricultural landscape. Species distribution models are used increasingly in conservation biology to provide such information. Most studies investigate the environmental pattern of species distribution, assuming that species records are reliable indicators of habitat suitability. However, ecological theory on source-sink dynamics and ecological traps points out that some individuals may be located outside the environmental bounds of their species’ reproductive niche. Those individuals could reduce model accuracy and limit model utility. Parameters related to the reproductive success of this shrike in Southern Belgium were integrated into a fine-scale presence-only modelling framework to demonstrate this problem and to address critical habitat requirements of this species relative to conservation management. Integrating reproductive parameters into the modelling framework showed that individuals occurred, but did not reproduce successfully, above a certain environmental threshold. This indicated that the reproductive niche of the shrike is ecologically narrower than standard practice in species distribution modelling would suggest. The major resources (nest sites availability, distance to human settlements, suitable perching sites, foraging areas and insect abundance) required for the reproduction of the red-backed shrike were quantified and ranked to offer concrete species-specific conservation management guidelines.