Autumn and winter 2009 were dramatic for owls in Finland. The tremendous amount of rodents in spring was totally gone by summer. Owl broods were big and until the end of summer there were many hungry mouths – yet there was no food. On the owls’ perspective such a situation is terrifying. However it is an unforgettable event for a birdwatcher. These birds of strictly sedentary nature had to relocate themselves to find a bite. Another option would have been to stay put and bite the dust. In such an occasion, human settlements with often abundant mice and rats are attractive to owls which come out of the woods to the reach of birdwatchers. Also in despair owls have to be active the whole day through to find food. This also make them easier to see for birders.
These times of trouble led to an irruption of ural owls almost never seen before. In Hanko Bird Observatory, far away from the nearest breeding grounds of ural owls, birds were seen at altogether 14 occasions during the autumn (six different birds caught from nets). It may sound a fairly small number but before year 2009 only 27 sightings had been made at the observatory since its start in 1979. Twelve of the sightings prior to year 2009 were made in 2006, when a similar irruption was witnessed. The irruption in 2006 might have been even stronger than in 2009 since 9 different individuals were caught with the standardized netting effort. The total number of irruptive migrants is difficult to assess since the birds seen in the field might or might not be the same individuals already caught in the nets.
Year 2009 had however an unfortunate difference compared to 2006. The becoming winter was a disaster for the owls. Snow coverage came early and it was thick even in the southernmost Finland. The thick snow blanket hid the already scarce rodents deep underneath it and out of reach for the owls. This resulted in as a devastating winter when dead owls were reported widely. Even goshawks were seen to catch starving and strengthless ural owls for prey. The Finnish Ringing Centre received reports of altogether 304 dead ringed ural owls between summer 2009 and late spring 2010. Of all the 4727 chicks ringed in 2009 no less than 147 (3.1%) were reported to have deceased between autumn 2009 and spring 2010. One can only ponder how many have died in total. In comparison of the owlets ringed in 2008 only 34 (1.0% of all the chicks ringed) were found dead during the following year and for chicks born in 2010 the amount was 6 (1.0%).
Every cloud has a silver lining
Such irruptions are commonly seen as death marches of owls where most of the birds fail to travel far enough to find food and eventually pass away. Despite the devastating situation in 2009 early summer this year gave delighting news. Unfortunately the news were also sad. An adult ural owl I had ringed on the autumn of starvation in Hanko Bird Observatory 18 October 2009 was found dead after colliding with a car three hundred kilometers North-East from Hanko. News are great because the bird has thus made it through the catastrophic winter and most likely returned to its breeding grounds. Probably the bird has even bred near the recovery site for seven years before the last fatal meeting with a passing by vehicle. Although the bird was an adult and thus probably already proven to be a good hunter, it’s is magnificent to see that a bird traveled as far South as Hanko had survived through the year of famine. After all it shows that the irruptions are not – at least always – death marches for the owls.