It has been observed that over the course of mating and raising a brood of chicks, a female green-rumped parrotlet's mass varies greatly. Female individuals gained up to 25% more mass before laying and maintained this mass through incubation until hatching began. The amount of mass lost over the brooding and fledging periods was dependent on the size of the brood. It is believed that this mass change is caused by a combination of brooding starvation, adaptation to a new lifestyle, and sexual activity.