Abstract
ABSTRACTCapsule: Monitoring of demographic parameters by volunteer ringers provides insight into the factors driving population changes in owls.Aims: To assess the value of national ringing, recapture and recovery data from volunteers to understand population dynamics.Methods: We analysed 49 years of ringing, recapture and recovery data from throughout Finland for Tawny Owls Strix aluco and Ural Owls Strix uralensis and compared them with annual population and productivity indices from other volunteer-based surveys.Results: Volunteer-based ringing data show that all aspects of the demography of Ural and Tawny Owls fluctuate dramatically in relation to an approximately three-year cycle of voles. When voles are abundant, a high proportion of owls breed and many young are produced; however, few of those young survive because vole populations crash the following winter. Survival of adults fluctuates less than that of young, suggesting that adults are better able to survive on alternative prey. In 2005, when vole populations remained high two years in row, many young were produced and survived, leading to a peak in owl breeding populations four years later at the top of the next vole cycle. This was immediately followed by a crash in populations suggesting a density-dependent interaction with vole abundance. Changing climate could affect owls both directly, by influencing winter survival, as well as indirectly through impacting prey availability.Conclusion: Encouraging similar, volunteer-based national-scale ringing efforts for owls elsewhere in Europe, especially for Tawny Owls which occur in most countries, would be a cost-effective way to understand how factors such as changing prey availability, climate and habitat availability are influencing the population levels of this and other raptors.
Highlights
Well-planned long-term ecological monitoring programmes provide the foundation for effective conservation and management of our natural world (Baillie 1990)
One of the most intensive studies has been the 30-year study in the northwestern United States of the demography of the Northern Spotted Owl Strix occidentalis. This very intensive study involved monitoring a range of demographic parameters with a large team of professional researchers, providing detailed information on the causes of population change to inform conservation planning for this threatened species (Forsman et al 2011)
We show how data collected by volunteers at a national scale can provide similar insight into raptor population dynamics
Summary
Well-planned long-term ecological monitoring programmes provide the foundation for effective conservation and management of our natural world (Baillie 1990). Dramatic declines in populations of several raptor species including Peregrine Falcons Falco peregrinus and Ospreys Pandion haliaetus provided strong evidence of the serious negative impacts of organic pesticides such as DDT (Dichlorodiphenyltrichloroethane) on ecosystems (Newton 1979, Risebrough 1986), which motivated efforts to control their use. One of the most intensive studies has been the 30-year study in the northwestern United States of the demography of the Northern Spotted Owl Strix occidentalis This very intensive (and expensive) study involved monitoring a range of demographic parameters with a large team of professional researchers, providing detailed information on the causes of population change to inform conservation planning for this threatened species (Forsman et al 2011). Many programmes run by the British Trust for Ornithology and other programmes elsewhere in Europe depend upon the efforts of volunteers (Baillie 1995, Baillie & Schaub 2009, Vrezec et al 2012, Robinson et al 2014, Derlink et al 2018)
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