The causes and consequences of variation in the incubation regimes of oviparous animals
remain unclear, despite having important fitness consequences. Avian incubation regimes
can be shortened by parents initiating incubation prior to clutch completion or prolonged
when there are gaps in the laying sequence. Here, we begin by quantifying variation
in the incubation regimes of three populations of blue titsCyanistes caeruleusfrom
the UK and Poland before examining the consequences of such variation for their hatching
and fledging success. We then investigate the mechanism causing such variation by
exploring the impact of local weather conditions on incubation regimes. The difference
between the expected and actual hatching dates of clutches was termed the "hatching
deviation" and this showed considerable variation. Hatching deviation was negatively
related to local temperature and clutch size. Hatching deviation affected hatching
success and hatching deviation, temperature, wind speed and clutch size affected fledging
success. Deviating from the expected laying and incubation regime caused lowered reproductive
success. The most successful birds were those that were able to lay one egg per day
and begin incubation upon clutch completion.
