Morphometric and behavioural data collected in blue tit pairs (7 traits)

Data collected in a wild population blue tits breeding in South-western Finland between 2003 and 2017. The names of males' and females' traits end, respectively with "_m" and "_f". Wing, tarsus, head-bill (Head) and tail lengths are in mm and weight is in g. Handling aggression (Aggression) is on a 1-5 scale and breath rate (BR) is expressed as a number of breaths per second. The birds' age at the time of measurement is in years.