Clutch size variation in Tawny Owls (Strix aluco) from adjacent valley systems: can this be used as a surrogate to investigate temporal and spatial variations in vole density?

Abstract

Research on Tawny Owls (Strix aluco) in Kielder Forest, northern England, since 1981 demonstrated that field voles (Microtus agrestis) were their most important food. Here, field voles exhibited a 3-4 year cycle of abundance, and mean clutch size in Tawny Owls was significantly related to vole abundance in March. In this analysis we use variations in clutch size as a surrogate to explore whether vole abundance was synchronized over a larger spatial scale, in this case between Kielder Forest and another forest (Kershope) in an adjacent valley system. We show that mean clutch sizes were synchronized between study areas during 1987-1992, but not subsequently (1993-1996). Synchrony was broken in 1993 when voles in Kielder experienced an extended low phase to the cycle resulting in 4 years between peaks, whereas vole cycles in Kershope continued with 3-year periodicity. Thus, since 1993 vole cycles in the two valley systems have been out-of-phase by 1 year. We discuss possible mechanisms whereby vole abundance in nearby areas can oscillate in- and out-of-phase with one another.

Parent Publication

• Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium

Citation

Petty, Steve J.; Fawkes, Billy L. 1997. Clutch size variation in Tawny Owls (Strix aluco) from adjacent valley systems: can this be used as a surrogate to investigate temporal and spatial variations in vole density?. In: Duncan, James R.; Johnson, David H.; Nicholls, Thomas H., eds. Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium. Gen. Tech. Rep. NC-190. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. 315-324.