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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The development of a population of Tengmalm's owl Aegolius funereus supported by nesting boxes in the years 1980 to 2000: Local breeding dispersion, reproductive output and nest site use.
Auteurs :	Ludwig Uphues, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (124(3) 2003)
Article en page(s) :	133-142
Résumé :	A population of Tengmalm's Owl has been observed since 1975 in an area of about 200 km2 south of the Lueneburger Heide (Lower Saxony). From 1980 onwards males (up to 1990), females and nestlings were ringed. From 1980 to 2000, a total of 441 surveyed breeding pairs fledged 971 young. 51% of the clutches were lost to predation, most of them to pine martens. The average number of the fledged young per nesting attempt (n = 441) was 2.19, while 4.32 young fledged per successful breeding attempt. Results were compared with those of the monitoring project "Raptors and Owls of Europe" and other studies. The problem of habitat fragmentation is of considerable importance for the population of Tengmalm's Owl. To connect isolated stands of mature trees containing natural Black Woodpecker cavities (426), a total of 383 nest boxes were offered to improve availability of breeding cavities. New boxes were added every year. Two aspects of Tengmalm's Owls' breeding strategy were noted in particular: 1. The entire breeding population consisted of about 10 subpopulations, in which breeding pairs occurred in close proximity. Size and location of such breeding areas changed from year to year, probably correlated with fluctuations in the number of small rodents and other factors. 2. Tengmalm's Owls clearly preferred to nest in new and/or relocated nest boxes and new natural (Black Woodpecker) cavities. Accordingly, breeding success in new cavities was significantly higher than in older ones. This study is the first to demonstrate this behaviour with sufficient data in Germany. Only 13% of nest boxes were still occupied by breeding pairs after 5 years, while 43% of new or relocated nest boxes were occupied by breeding pairs in the first year and a further 24% in the second year. When clutches were destroyed, later assessment identified pine marten as the main predator. The risk of nest predation increases with the age of a nest cavity. These facts support the hypothesis, that the pine marten memorizes the location of cavities in its home range in which it found prey and will preferentially revisit these cavities in later years. Tengmalm's Owls, therefore, can minimize predation pressure to some extend by changing breeding cavities between years. This strategy seems to be operating at least in areas where pine martens are important predators, a finding confirmed in a long-term study in southern Norway (Sonerud 1985, 1993).

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