Timing and stages of nest-building by Marsh Tits (Poecile palustris) in a primeval forest.

The date of laying the first egg in a nest is conventionally taken as the date of breeding commencement in birds. However, to start egg-laying most birds first have to build a nest. As nest construction consumes time and energy, it could interfere with other activities, and beginning nest-building too late could delay egg-laying. How birds decide on when to begin nest building and how they allocate time to the different stages of the construction process remains poorly understood. Here I analyse factors influencing the timing of nest-building initiation and temporal arrangement of construction stages in the Marsh Tit (Poecile palustris), a small nonexcavating hole-nester. Data were gathered in primeval fragments of the Białowie a National Park (Eastern Poland). The temporal pattern of Marsh Tit nest building behaviour was highly versatile, varying between and within years (younger females commenced later). In warm springs, nest building started earlier but birds built nests at slower rates than in the late seasons. Marsh Tits often built nests ahead of time appropriate for egg laying, indicating that the timing of breeding in this population was not constrained by nest building activities. It is suggested that the tactic 'build in advance, then wait for the right time for laying' could be widespread among sedentary birds, especially among ones which build nests in enclosed places. [ABSTRACT FROM AUTHOR]