Long-term ecological monitoring reveals sharp owl declines in farmlands, indicating agricultural intensification drives population losses through prey habitat depletion.
Key Points
Investigate how agricultural intensification and fluctuating prey abundance influence the breeding density, reproductive success, and long-term population trends of Short-eared Owls.
Monitored Short-eared Owl breeding parameters (density, clutch size, brood size, nest failure causes) and vole prey abundance over a 30-year period (1977–2006) in western Finland.
Extended monitoring across a broader 1,000-km² area through 2023 to capture a 47-year population trend alongside temporal landscape changes in grassy habitats.
Annual breeding density ranged from 0.0 to 1.5 nests/km² (mean 0.35), with higher breeding density, clutch sizes (2.5 to 8.2 eggs), and brood sizes (0.7 to 4.4 nestlings) occurring during peaks in spring vole abundance.
Over the 47-year monitoring period, the local breeding owl population declined by more than 50% (mean annual decrease of 2.8%), primarily driven by agricultural activities and predation as sources of nest failure.
Landscape intensification, marked by converting hay and pasture to crops and removing open ditches, led to a 46% reduction in grassy foraging habitats supporting voles.