Pygmy owls drafted in to control unprecedented vole damage in Savo Province

Unique research project would speak in favour of use of bird boxes and birds of prey

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It has been noted earlier that this year is a particularly bad one for moles and voles in Finland, with widespread damage being reported to tree saplings, and also to strawberry plants in the important growing area of Suonenjoki.
      The eternal question within forestry circles has been whether the voles ravishing sapling stands can be kept at bay by favouring birds of prey.
      The general scientific stand has been: no, they cannot.
      Now there seems to be an answer to the question, and typical of science, the answer is somewhat enigmatic. The detective story has an intriguing plot.
     
Last summer, forestry researchers set up bird boxes for the Eurasian pygmy owl (Glaucidium passerinum) next to 50 sapling stands in commercial forests in Suonenjoki, Karttula, Rautalampi, and Pieksämäki.
      The smallest owl in Finland and in Europe, not much larger than a bullfinch, has a peculiar habit of storing its prey in holes and hollows.
      In the winter’s calculation the pygmy owls’ food storages were discovered in the bird boxes of 18 sapling stands. More than 90 per cent of the 600 stored kills were field voles (Microtus agrestis).
      “That sounds like a large figure, but in fact an area of just one hectare can easily house that number of field voles”, explains researcher Otso Huitu of the Finnish Forest Research Institute METLA.
     
Once the snow had melted, 5,000 marked spruce saplings in the area were checked. Of them 42 per cent were damaged by voles.
      "The setting up of owl boxes reduced the amount of damage in those sapling stands, which - according to our test trapping - housed only a few voles for what was a peak year”, reveals forestry student Tiia Puukila, who is preparing her dissertation on the subject.
      Where there were a huge number of voles, not even the owls or the owl boxes were of any help.
     
Researchers are excited about the results.
      Initially and very cautiously they say that “the result would strongly suggest that in separate smallish sapling stands the pygmy owl might well succeed in limiting vole damages when the size of the vole population remains moderate.”
      Not quite everything can be revealed just yet, for in time the results will be offered to a respected scientific publication.
      A scientist also has a rational attitude towards nature. Still, Huitu frets on behalf of the tens of thousands of Finnish forest owners.
      “According to the estimates by forestry centres, 18,000 hectares of sapling stands have sustained considerable vole damage.”
      That is a pretty bleak record. During the previous vole peak in 2005-2006, around 5,000 hectares suffered from the blight, and already that was considered a disaster.
      This time around, the worst-affected areas are situated in the provinces of Uusimaa, Häme, Central Finland, and Savo.
     
The most calamitous of all the moles and voles has been the field vole.
      It peels the pine and spruce saplings, leaving them as dried-up mummies.
      The bank vole (Myodes glareolus) also climbs larger trees and cuts off the top and branch offshoots.
      According to METLA statistics from the past 30 years, never before has Finland’s vole population been as large as it was at the end of 2008. The latest signs would suggest, however, that the population is about to collapse.


Previously in HS International Edition:
  A quarter of young strawberry plants in Suonenjoki region destroyed by voles (22.5.2009)

Links:
  Field vole (Wikipedia)
  Bank vole (Wikipedia)

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