REDUCED PREDATION BY NEST BOX RELOCATION - DIFFERENTIAL EFFECT ON TENGMALM OWL NESTS AND ARTIFICIAL NESTS

The hypothesis that the frequency of predation by pine marten Martes m artes on nests or Tengmalm's Owl Aegolius funereus rises with cavity a ge as a result of long-term spatial memory of the predator predicts th at relocation of nest boxes should lower the frequency of predation. P rior to a microtine rodent population peak I relocated a randomly assi gned half of a population of 12 year-old nest boxes. Prior to the next microtine peak I reversed the experiment by relocating the control bo xes. tn both cases, predation on Tengmalm's Owl nests was reduced in t he relocated boxes and unchanged in the unmoved ones. To test if this predation pattern is mimicked in artificial nests, I relocated the exp erimental boxes once more two years after the first relocation, and us ed the two intermediate microtine low years, when no Tengmalm's Owl ne sted. Predation on artificial nests was lower in relocated boxes, but not in unmoved boxes, compared with predation on Tengmalm's Owl nests in the same boxes before the first relocation. However, whereas predat ion was lower in relocated than in unmoved boxes for Tengmalm's Owl ne sts (22% vs 83%), this was not so for artificial nests (54% vs 58%). T his shows that the results of experiments using artificial nests to re veal patterns of nest predation in tree cavities should be interpreted with caution.