Effect of nest site on nest survival in the Dunnock Prunella modularis

Abstract

Nest survival and breeding success were studied in relation to nest site at 134 Dunnock nests in southern Finland. The nests were grouped according to three site categories : 1) small spruce, 2) shrub, and 3) heap of spruce twigs and branches (brush pile). Of the 110 nests under observation during the egg stage, 56 failed ; 54 failures were attributable to predation. During the egg stage the daily survival rate of a nest was 91.3% in spruces, 91 .2% in shrubs, and significantly higher, 96.7%, in brush piles. The probability of a nest surviving throughout the egg stage was 24%, 23% and 59%, in spruces, shrubs and brush piles, respectively . The hatchability of eggs varied from 89.3% in spruces to 95 .4% in brush piles, but the differences were non-significant. During nestling stage, 10 out of 77 nests were destroyed by predators, but no other failures were observed. The daily survival rate of nests varied from 96.8% in spruces to 99.1 % in shrubs, and the daily survival rate of nestlings exceeded 99%, irrespective of the nest site . The differences were non-significant. The size of first clutches did not vary between the nest sites. On average, successful nests were better concealed both from above and from the sides than failed nests, but no other differences in nest site characteristics were found. The brush pile nests were better concealed from the sides than other nests . Dunnocks used nest sites that offered better cover and were surrounded by denser vegetation than potential but unoccupied sites.