YR = Year 

PID = Individual pull ID

NY = Nest ID on each year

SG = Synchronous group

EG = Experimental group

BS = Brood size

CR = Rank of the nestling (the nestling that hatched first was assigned the highest rank, i.e., rank 1)

SX = Sex of the individual (0 = females, 1 = males)

MTN = Maximum temperature in the nest (Tnest; Celsius) between the two monitoring sessions encompassing the heatwave event

NM = Nestling mortality during the heatwave (0 = alive after the heatwave; 1 = dead)