Preliminary results of the comparative analysis of the mass, size and thermal insulation of song thrush (Turdus philomelos) nests in the center and north of the breeding range

The main aim of the investigation was to compare the adaptive characteristics variations of nests associated with their thermal insulation depending on geographical location. It was produced on the example of Song Thrushes’ (Turdus philomelos) nests dwelling in the center and north of the breeding range. The data were collected in the Republic of Karelia, North-Western Russia (64º27’N, 30º17’E), in 2015, and in the Republic of Mordovia, Central Russia (54º44’N, 45º30’E) in 2016. At the first stage of the study, the main size parameters and mass of nests were estimated and compared as well as calculated values of volume and construction density from the different parts of the area. At the second stage, the comparative analysis of thermal fields distribution on the nest surface was carried out using special hitting of the inside part of the nest with a spheroid thermostat. This allowed to compare thermal insulation characteristics of all the constructions. Our preliminary results showed that the mass and size parameters of the nests from the centre and periphery of the breeding range were statistically identical except such parameter, as nest height. In the north, the nest height was significantly greater than in the centre, owing to increasing thickness of the nest bottom. The volume of the nests in the North was greater than in the central parts of the range, too. The latter, due to indistinction in mass, could be explained by the changes in distribution of nest materials within the whole construction as a result of increasing nest thickness and decreasing nests density in the North. This leads to the improvement of thermal insulation efficiency of northern nests as compared with the nests in a region to the South.