Relocation of nest boxes reduces nest predation by pine marten Martes martes on the Castelporziano Estate, Italy
Sorace A., Petrassi F. & Consiglio C. (2004) Long-distance relocation of nestboxes reduces nest predation by pine marten Martes martes. Bird Study, 51, 119-124
Background
Nest boxes of small-sized hole-nesting birds may suffer high rates of clutch predation by mammals. This experiment examined if pine marten Martes martes predation increased with the age of nest boxes and whether predation is affected by distance boxes are relocated from where predation events occurred the previous year.
Action
Study site: The study was undertaken in four consecutive breeding seasons in woodland on the Italian Tyrrhenian coast. Wooden nest boxes (14 x 14 x 22 cm; 3.5 cm diameter entrance hole) were attached to trees in plots of i) Turkey oak Quercus cerris and Hungarian oak Q.frainetto dominated deciduous woodland (800 ha), and ii) Holm oak Q.ilex woodland (392 ha). The trees in both were 50-70 years old but the former had some older trees present and a more developed undergrowth.
Nest box placement: In winter 1991, 31 boxes were placed in a deciduous woodland plot. Six cases of predation by pine marten upon clutches of tits Parus spp. were observed in 1992-1994; three in the last year (25% of clutches).
In the 1995-98 period, boxes were placed in order to have plots with i) new boxes (first spring of placement) ii) boxes placed at short (approx. 100 m) and long distance (approx. 800-3,000 m) from a plot of the same habitat where in the previous year pine marten nest predation had been recorded.
In the spring of 1996 and 1997, the boxes used in spring 1995 were moved to new plots rather than using new boxes, so that plots could be compared by using boxes with similar characteristics (i.e. smell, colour). After spring 1995, boxes were also relocated at short and long distances from one of the holm oak plots as there had been a case of predation by a pine marten on an adult female great tit Parus major in one of the boxes. This also gave a balanced experimental set-up between the two study habitats.
In February 1998, 16 boxes were newly placed in one of the deciduous woodland plots to evaluate whether the risk of predation was the same a year after box absence. Box placement was undertaken in February each year when the contents of all boxes were also emptied. Boxes relocated to a new plot were not visible from the original plot. Boxes were placed at 50 m intervals, fixing them to oak trees about 3 m above ground ensuring that they were not covered by vegetation. In each of the study years, weekly visits were made to record cases of predation.
Consequences
Nest box predation: A total of 67 great tit and blue tit P.caerulea clutches were predated by pine martens. Predation was higher in older boxes (second compared with first year of placement). The predation rate on short-distance relocated boxes was higher than on the long-distance relocated boxes. There was no significant difference between predation rates between the two woodland habitats.
In one deciduous plot, after six years of placement (1991-96) 76% of boxes were predated by pine martens with the predation rate increasing from the first to sixth year. In this plot in spring 1998, a year after nestbox absence, predation was very high on clutches in replaced nestboxes, 50% of these being predated.
The results also indicate that predation by snakes was also higher in the older boxes, two boxes being predated in the first year and eight in the second year of placement.
Conclusion: This study suggests that moving nest boxes may increase the reproductive success of small-sized hole-nesting passerine birds through decreased predation rates.
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