Monros J.S., Belda E.J. & Barba E. (1998) Delays of the hatching dates in Great Tits Parus major: Effects on breeding performance. ARDEA 86 (2): 213-220

The effects of delays of hatching date, caused by temporary interruptions or lengthening of breeding activities such as nest building, laying or incubation, on several fitness-related components were studied in a Great Tit Parus major population in eastern Spain. Hatching delays were relatively more frequent during an episode of bad weather. Delays of hatching dates did not negatively affect any of the fitness-related factors examined (hatching and breeding success, fledgling mass, and local return rates of young). The analysis of selection differentials showed that the delay in hatching dates meant that the population hatched their eggs closer to the mean hatching date of recruits than if the delays had not occurred. Our results suggest that some delays in the hatching date could be beneficial for the birds, since they seemed to allow a better adjustment to changes in environmental conditions