Acta ornithoecologica • Jena 4.2-4 (2001) 269-278
Detailed observations were made of Cainism in a Lesser Spotted Eagle's (LSE) nest, whereby this procedure generally leads to the death of the second chick a few days after hatching. The time-lapse between hatchings amounted to two and a half days (60 hours). At the time of hatching the chicks weighed 64 und 58 g respectively. During the first and second days after the second chick (Abel) hatched, no signs of Aggression could be observed and herb chicks received a liberal supply of food. On the third day, however, herb chicks were strenuously fighting, with Abel being the first to attack. On the fourth day the female was displaying an unmistakable tendency to favour the older chick (Cain), which clearly held a stronger attraction for her. On one occasion the feeding by the female abruptly ended even though Abel was still actively begging for food. On this day Abel was indeed still given food, but its begging and its own attacks were, however, very haphazard. At four days old Abel weighed 12 g less than it did on hatching. This chick probably died the next day, even though there was an abundance of food in the nest.
Observations at another nest (see Table 1), in which Abel had reached an age of about three weeks, confirmed previous findings by experimental translocation that the weaker chick's acceptance of intimidation is ultimately responsible for its death when other factors (smaller weight at hatching, later hatching date resulting in less adroitness and tenacity at feeding times, neglect by the female) do riet lead to it.
The three cases so far considered, in which the second chick could be closely observed from hatching to death, show that Cainism in the LSE can take a variable course. This is amply confirmed by the case under study in which Abel survived for up to three weeks.
The existence of Cainism could be explained by the LSE´s being today at an intermediate stage in its evolution, of transition from two-egg to one-egg clutches.
Abstract: The following factors are responsible for Cainism (fatal Cain-and-Abel struggle) in the Lesser Spotted Eagle:
Key words: Aquila pomarina, Lesser Spotted Eagle, cainism, Cain-and-Abel struggle, evolution.