Bad News and Good News: Population Changes of Finnish Owls During 1982–2007

Abstract

In Finland, monitoring of ‘common’ birds of prey is based on two projects run by the Finnish Ringing Centre: the Raptor Grid (since 1982) and Raptor Questionnaire (since 1986). The Raptor Grid has produced sufficient data for analysing population trends in six of ten owl species. The overall trend during 1982–2007 was significantly negative in the Eagle Owl Bubo bubo (-2.2% per year), Long-eared Owl Asio otus (-4.7%) and Tengmalm's Owl Aegolius funereus (-3.1%), and significantly positive in the Ural Owl Strix uralensis ( 1%); no significant trend was detected in the Pygmy Owl Glaucidium passerinum or Tawny Owl Strix aluco. The Eagle Owl population increased to the middle of 1990s, but has since decreased by 5% per year. The decrease coincides with the closing of 90% of local open rubbish dumps, which offered a stable and rich food supply to the Eagle Owls. The decrease in the Tengmalm's Owls can partly be attributed to the decrease in the amount of old forest. The Pygmy Owl population increased steeply (>5% per year) during 1994–2003, then crashed following a mass invasion and has since started to recover. The geographical distribution of the Raptor Grid study plots is not suitable for monitoring the northern nomadic species like the Snowy Owl Bubo scandiacus, Northern Hawk-Owl Surnia ulula, Great Grey Owl Strix nebulosa and Short-eared Owl Asio flammeus. Annual totals of active nests and occupied territories reported with the Raptor Questionnaire do not indicate any long-term population changes of these species. However, intensive cooperation over larger areas across national boundaries in northern Europe is urgently needed for reliable monitoring of these nomadic owls.