Position of Blackbird ( Turdus Merula ) Nests in Orange Trees

Abstract

Nest placement affects the risk of predation and determines the microclimate for incubation. We have analysed the nest placement of the blackbird nests and the temperatures at which they are exposed in an orange plantation from Eastern Spain. The data come from a 16.9 ha of an orange plantation. In this plot, nest searching techniques were applied. Nest placement and the temperatures at midday were recorded from a sample of 84 nests. Furthermore, a sample of 16 nests was used to determine the daily variation between 8:00 and 20:00 hours. We measured the nest height, tree height, and distance from the tree centre to the nest, and the length of the longest branch. The temperatures inside the nest cup and of the surrounding air temperatures were also obtained. The range of the orange tree height was 82-425 cm (mean = 234.0 cm). The length range of the longest branch was 11-311 cm (mean = 136.4). The nests were placed at heights between 41 and 223 cm (mean = 134.4) and the distance from the centre of the tree varied from 8 to 233 (mean = 126.5). There was no variation in the nest heights and distances from the trunk to the nest place as the breeding season progresses. The air temperature (T_at) and the nest temperature (T_ict) at midday increases as the breeding season progresses but the difference between T_at and T_ict did not vary according to the time in the breeding season. The daily difference between the air and the nest temperatures increased from 08:00h to 12:00h and then decreased. Only three nests out of the 100 nests sampled were successful inbreeding.