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

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

Habitat preferences and territory size of the Dunnock Prunella modularis in southern Finland

An area of 4.08 km2 was studied in Heinola, southern Finland, mainly in 1984-85. The mean song polygon size was 1 .53 ha (SD 0.42 ha, n=51) and, on average, unpaired males defended 0.27 ha smaller territories than paired males. The territories defended by two males were largest, averaging 2.17 ha (SD 0.54 ha, n=3) . Spruce-dominated forests were used disproportionatelly oftenbythe Dunnock. Statistically significant differences between the territories and control quadrats were found in 9 outof 18 habitat-structure variables. The most striking difference was the greatnumber of small spruces and spruce bushes in the territories . In addition medium-sized spruces were more numerous, the dominant trees were taller, and the canopy cover denser in the territories . In 49 outof 59 territories an edge of some kind was presentinside the territory or formed a boundary for the territory. In the upper tree layer of the territories, spruce was very prominent, but in the lower tree layer deciduous trees (mainly birch) were almost as numerous. In the bush layer deciduous bushes were most abundant . It is concluded that small spruces and spruce or juniper bushes are essential features of the habitat for the Dunnock; spruce bushes are important nest sites, and Dunnocks also search for food in thickcover under the deciduous and coniferous bushes . The males arriving earlypreferred young open bushy forests . In biandrous territories, the edge was nearer the centre and bushes were more numerous than in territories defended by one male

Population increase and breeding biology of the Dunnock Prunella modularis in southern Finland

The breeding biology ofthe Dunnock (Prunella modularis) was studied on the basis of 517 nest cards gathered mainly from southern Finland during 1954-87. The habitats used included several kinds offorests, spruce and mixed forests being the mostcommon. Most nests were located in spruce bushes (62.5% of nests) or in juniper bushes (15.3%). Laying of the firstclutches started on averageon 16 May(SD=7.0 days, n=151) ; there was no difference between habitats, but northwards the laying was delayed. Due to the second and thereplacementclutches, the laying period continued until late July ; thelatest clutches were commenced on 23 July . Mean clutch size was 5.44 (SD=0.69, n=97) in June, but significantly lower in May (5 .11, SD=0.61, n=151) and July (4 .14, SD=0.62, n=21). Clutch size did notvary significantly between habitats, latitudinal zones, or cool and warm years . The probability of an egg giving rise to a fledgling was 0.37. The daily survival probability ofnestlings was significantly higher than that ofeggs. The breeding success increased with advancement of season . The overall survival probability was lower in cool (0 .20) than in warm (0 .46) Mays. The low survival of eggs during cool weather was attributed to increased predation of conspicuously coloured eggs . There was no difference in survival probability between habitats during the egg stage. The results are briefly discussed with respect to the recent population increase ofthe Dunnock in Finland