Hierarchy of Factors that Determine the Timing of the Arrival of Passeriformes in the Ob Forested Tundra

Abstract

This paper analyzes the factors that determine the timing of the spring arrival of passerine birds in the nesting area, i.e., the Lower Ob Region. For the period 1971–2015, a reliable negative trend to an arrival shift to earlier dates for seven out of 16 species, an unreliable shift for six species, and a positive trend for three species were found. Using cluster analysis, three groups of species with similar arrival dynamics were identified. The temperature in the study area at the beginning of the arrival of all species increased with the approach to the end of the period analyzed (1971–2015) in parallel with the growing spring average monthly temperatures. Significant correlations of the starting dates of bird arrival with spring air temperatures (mainly in May), dates of ice passage along the Ob River, and the length of the migration route of the species were revealed. The relationship of the starting date of arrival in most species with the average daily air temperature directly on the day of arrival is weakly expressed. Thus, the main factors affecting the arrival dates are the average monthly spring air temperatures, primarily in May. The North Atlantic Oscillation Global Weather Index (NAO) is much less significant.