Note sul cleptoparassitismo dello Storno Sturnus vulgaris in periodo riproduttivo

Trotta M.



Abstract:

During a study on the diet of Starling Sturnus vulgaris, several cases of kleptoparasitism, both intraspecific and interspecific, were observed. Information was collected on the techniques and frequency of success, as well as on the taxa of the stolen prey. In the case of intraspecific kleptoparasitism a technique of “threat” was applied which had low energy cost but produced a rather low percentage of success (10,9%). The fact that the prey was given up without any further aggression could be due to the possible existence of a hierarchy within the colony, containing dominant members who have priority over the young and lower ranks. In interspecific kleptoparasitism, which occurred only against Blackbird Turdus merula, the percentage of success was 84%. This was much higher than that recorded by Källander (1988) on Lapwing Vanellus vanellus which unlike Blackbird, used a variety of strategies to escape the attack of the Starling, sometimes crowned with success. In interspecific kleptoparasitism, techniques of “attack” and “chase” were used. The high energy cost incurred by the Starling was compensated by the high percentage of success gained using these two techniques (91,3%) and by the protein value of the stolen prey: 76,2% being earthworms. During the rearing of the young, catching of earthworms was carried out exclusively by kleptoparasitising Blackbirds.