More than 1000 pairs of tree-nesting Peregrines once occupied the European lowlands from Germany to Russia. In northern and eastern Germany a population of about 500 pairs of pure tree-nesters ...existed among which only a very few occasionally nested on buildings and cliffs. This population which was definitely affected by toxic agro-chemicals in its nutritional chain became completely extinct after 1972 throughout the whole tree-nesting area. The habit of tree-nesting is definitely based on imprinting and tradition. On this premise a reintroduction project was started in 1990 in north eastern Germany in which young Peregrines reared in captivity were imprinted to tree-nesting habits before and after their release. This will be continued until 20 sites are occupied by tree-nesters in Germany. Up to now (2000) 201 young Peregrines were released successfully; an additional 29 fledglings came from 3 wild broods found established in old pine woods since 1996. All Peregrines of the new eastern German population which has been established since 1981 are individually marked by ring combinations which permit the reading by telescopic means of whether the birds are coming from trees, buildings, or cliffs and are released or fledged from wild broods. Also the year and site they came from is identifiable. To monitor the success of the project, a table of survival was calculated (Tab. 1) which shows that 22 adult Peregrines may exist from all released and wild fledged birds together in the year 2000. All the falcons at the 3 tree-nesting sites were found to be released from the project, thus confirming the effectiveness of imprinting to this type of nesting. Another 11 falcons from the project group were identified as mates at buildings and cliffs. This indicates a 50% return to the inborn nesting type. However, up to now not a single falcon fledged from cliffs or buildings changed to tree-nesting. The exchange between falcons of different nesting types corresponds to a one way road with the blocked direction toward tree-nesting. As a consequence of this new finding a tree-nesting population can only become established and remain self-sustained in areas without or with very scarce nesting sites on buildings or cliffs. Nesting sites on buildings should not be offered in tree-nesting areas! This initial success can only be maintained if more young Peregrines fledge from trees than from buildings in the tree-nesting areas. On all accounts an early protection against losses of species should be preferred to expensive and not always practicable reintroduction.PUBLICATION ABSTRACT
