Selezione di habitat e riproduzione dell’Averla capirossa, Lanius senator, nel Lazio – Italia centrale

Guerrieri G., Castaldi A.



Abstract:

The reproductive biology of Woodchat Shrike, Lanius senator, has been studied for seven years (1992-1998) in a sample area of Central Italy. The settlement of the species in Latium, is influenced by May rainfall. The pairs number, greatly variable (+/- 50 %), varies between 1.40 and 2.04 pairs/km2 (max. 5 pairs/km2). Woodchat Shrike, sympatric with two other species of the same genus which nest in Italy (L. collurio, L. minor), seems to prefer xerophytic pastures with scattered shrubs (20 %). The interspecific competition is less intense than the intraspecific one. Nests are preferably located on shrubs which have a mean height of 3.39 m (S.D. = 1.31) and the mean height of nest site is 1.97 m (S.D. = 0.64). During laying of replacement clutches, when pairs are consolidated, singing activity is significantly reduced. If the first hutching is unsuccessful, Woodchat Shrike avoids to place the second nest where predators are facilitated. Average clutch size (4.61; S.D. = 1.01) is one of the lowest in the reproductive areas. The 4.41 of the eggs is sterile. The 41.5 % of the pairs fails the first reproduction and the 13.6 % is not able to reproduce at all. The average number of juv. / pairs successful in hutching is 3.1 juv./pairs (S.D. = 1.16; juv./eggs = 0.575). In this region, adults seem to move away from the reproductive area sooner than juvenes.