Although two chicks are hatched in about 75% of Lesser Spotted Eagle eyries there is, to date, no documentarv record of a single case where two eaglets left the nest (MEYBURG 1970). Therefore in 1968 and 1969 in Slovakia, the author conducted experiments to establish whether, with human aid, the second chick, too, could be reared to the point of leaving the eyrie, thereby affording an almost unique possibility for protecting a type of eagle threatened with extinction in some countries.
The positive result, whose pros and cons for wider application are discussed in detail, is very encouraging. lt is therefore urged that, in areas where the L. S. E. is decreasing, the method successfully tried out by the author be applied to the largest possible number of L. S. E. eyries, the procedure being as follows:
In each case one of the newly-hatched chicks or one of the eggs - which then has to be artificially incubated further - must be transferred from a L. S. E. eyrie to that of another larger bird of prey - Common Buzzard, Black Kite, Red Kite or Goshawk. The young L. S. E. will be reared by its foster-parents instead of their own young, which must be removed simultaneously. Shortly before it is due to leave the eyrie, it must be returned to a L. S. E. eyrie containing an eaglet at approximately the same stage of development. A few days later both young eagles leave the eyrie and continue to be cared for by the adults until they become independent. Chicks taken from the eyrie of the foster-parents should be distributed among eyries of the same species which contain only a few young birds.
Details of the method arc described and discussed.
In 1968 two second young birds taken from two L. S. E. eyries were reared by two pairs of Black Kites. In 1969 L. S. E. eggs were successfully incubated bv artificial means and one chick was placed in the nest of a Common Buzzard. Experience gained in these experiments is described in detail. Another question dealt with is why a different procedure, e. g. exchanging the young of different eyries so that two eagles of equal size are brought together, is unsuccessful.
In 1970 DANKO (pers. comm.), quite independently of the author, applied this method successfully to an eyrie in eastern Slovakia.
lt is recommended that experiments be made with other threatened species which present similar conditions, e. g. in Europe the Golden Engle (Aquila chrysaetos) and the Bearded Vulture (Gypaetus barbatus).