Time-saving mechanisms in the reproduction of Marsh Tits (Parus palustris)

Abstract

Producing young late in the season is very costly in Marsh Tits, therefore any means which allow late-laying females to compensate for an initial delay are highly advantageous. Any attempts to make up for the initial delay should result in shorter breeding cycles late in the season and in shorter reproductive cycles in late-laying females. A shortening of the nesting cycle should be achievable via reduction of the clutch size or by shortening the duration of the incubation and/or nestling periods. These predictions are examined using data from an extensive study of Marsh Tits carried out in remnants of primaeval European forest (Bialowieza National Park, E Poland). As anticipated, the breeding cycle late in the seasons was significantly shorter. This was due to a decline in clutch size, and shortening of the incubation period. The shortening of the cycle occurred also within a season, late-laying birds had significantly shorter cycles than early-laying ones. This was due to a very steep seasonal decline in clutch size and, to a lesser extent, by a shortened incubation period. With the five day overall difference, the late-laying birds could compensate for up to a third of the initial delay in egg-laying, a substantial saving of time. Young females commenced laying about two days later than older ones; as predicted, they laid smaller clutches but contrary to the predictions, they incubated for longer. The nestling period showed no relationship with season neither among years nor within a single year.