Interspecific competition limits larders of pygmy owls Glaucidium passerinum

To test whether competitive and predatory interactions limit larder size we erected pygmy owl Glaucidium passerinum nest-boxes for hoarding with 45 mm entrance diameter near and far (>2 km) from Tengmalm's owl Aegolius funereus nest-boxes with >80 mm entrance diameter during early autumn. We found larders of pygmy owls in similar frequency in both near and far plots (41 vs. 42% of plots), but in near plots the number and biomass of cached prey by pygmy owls were lower. These results suggest that there is competition for food between these two owl species and/or that food caching behaviour of pygmy owls is disturbed by larger Tengmalm's owls.