Cainism, nestling management in Germany in 2004-2007 and satellite tracking of juveniles in the Lesser Spotted Eagle (Aquila pomarina)
The Lesser Spotted Eagle belongs to a species with obligatory cainism, which means that in the natural state it is rare that two young eagles fledge, although as a rule two chick's hatch. The breeding population in Germany is at the western edge of the species' range and is declining (a 23% decrease between 1993 and 2007). Local extinction can be anticipated and therefore nestling management has been implemented in the German federal state of Brandenburg since 2004 as a conservation measure by using human intervention to prevent the death of the younger sibling. This is in addition to other methods such as nest-site protection, habitat preservation, legislation etc. Furthermore, in 2007, second hatched eagle chicks (Abels) from Latvia were translocated for the first time. The managed pairs (nests physically inspected) were on average more successful than the unmanaged pairs (nests not physically inspected). It cannot be determined as to whether the inspection of the nests had a negative effect on breeding. Breeding success of the pairs present in Brandenburg, including non-breeders, increased by 57 % in 2007 due to nestling management, and that of the managed pairs alone by 67 %. In 2007 the behaviour of six young eagles was studied using satellite telemetry. This study determined that the Abels migrated as well as the first hatched eagle chicks (Cains), and that their survival chances were equally good. The Abels imported from Latvia migrated in two out of three cases along the same route as the German Lesser Spotted Eagles to the Bosporus. One Latvian Abel which fledged in Germany was tracked by satellite to Zambia where many Lesser Spotted Eagles winter. A German Abel wintered North of the Equator in the Sudan and neighbouring countries for over six months and started its return migration on 27 April 2008.
After the disappearance of the Peregrine Falcon during the DDT era, the re-colonization of Eastern Germany from 1981 was accompanied by colour-ringing of a high percentage of juveniles and systematic identification of these individuals on their later nest-sites. Before that period there were two geographically distinct subpopulations: tree-breeders in the north, and cliff-breeders in the south. We were able to restore the tree breeders’ tradition by imprinting nestlings at stick nests in forests. Today, besides cliff- and tree-breeders there are also nest-sites on buildings and lattice structures. The population is increasing including all nest-site types. Here, we analyse nesting habitat choice with respect to the natal habitat of birds. The exchange between the four nest-site types is limited. Habitat fidelity was high in birds fledged on cliffs (95%) and on buildings (81%). The sample size for lattice structures is still too low for deeper analyses. The fixation towards trees was stable only in 56% of birds, and higher for males than for females. The influx from other habitat types is very limited and hardly supports the tree breeders’ subpopulation. A growing number of tree-breeders go along with higher habitat fidelity which is stabilizing their sub-population.