Nest Hole Shift in Tengmalm's Owl Aegolius funereus as Defence Against Nest Predation Involving Long-Term Memory in the Predator

Abstract

In SE Norway, 48% of Tengmalm owl clutches were preyed upon; of these at least 70% and possibly all, were taken by pine martens Martes martes. Frequency of predation increased with nest box age, but was independent of nest density, which fluctuated in parallel with numbers of small rodents, the staple prey of Tengmalm's owls and pine martens. Tengmalm's owl clutches had a higher probability of being preyed upon in nest boxes where the previous clutch had been taken than in boxes where there had been a successful nesting the previous year. Pine martens thus did not encounter nest boxes randomly, but revisited those that they had found previously. Tengmalm's owls preferred to nest in new boxes, and a majority of the females shifted nest hole between successful nestings. Clutches initiated in March were in newer boxes than were later clutches, and were thus less exposed to predation. This predation situation will select for owl individuals which move to another hole after having a clutch preyed upon. If new holes become available each year it will also select for individuals which shift nest hole between successful nesting and prefer nesting in new holes.