Sopravvivenza e filopatria della Rondine (Hirundo rustica) in Italia settentrionale

Ferro G. & Boano G.

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From 1988 to 1996 13024 Swallows were ringed in a rural area of about 65 Km2 square near Bra (Italy, NW). The analysis of recaptures shows a high breeding-site philopatry: 93% of adults recaptured in the study area (15% of the adults ringed) returned to the previous breeding site. Natal philopatry was low and only 1% of the birds ringed as nestling were recaptured in successive years in the study area, and 80% of these chose a different site from that of their birth. In view of the high breeding-site philopatry we would expect that the permanent emigration of breeding birds from the area to be very low, so that the capture-mark-recapture survival estimate for the adults (36%, s.e 2%), obtained using Jolly-Seber models, will have provided a good estimate of adult survival. In contrast, the survival estimate for juveniles (3%) is certainly strongly negatively biased due to the low natal philopatry (i.e. high emigration rate). Capture-mark-recapture data of sexed adults also permitted the differential survival rates of males (37%, s.e. 3%) and females (26%, s.e. 2%) estimates. The adult survival estimate is comparable to other estimates obtained with ringing recoveries and is therefore probably unaffected by the emigration rate, but the lower females survival rate, if not due to a higher emigration rate than males, could explain the observed population decline in spite of a normal breeding success.