Avian clutch size of increasing clutch size with increasing latitude. The proximate and ultimate causes for this pattern have been a subject of intense debate involving the ideas of group and individual selection. David Lack observed a direct relationship between latitude and avian clutch size. Birds near the equator laid approximately half as many eggs as those that resided in northern temperate habitats. He observed an increasing clutch-size from the equator towards the poles (something he referred to as the “latitude trend”) for many passerine (perching) birds, near-passerine (tree-dwelling) birds and in various other groups: Strigiformes, Falconiformes, Ciconiiformes, Laridae, Ralliformes, Galliformes, Podicipedifomes, and
Angry Birds Friends or to acquire additional bird slingers. In addition, the mobile version includes four power-up practice levels where there are infinite power-ups available for use. In February 2012, the episode "Surf and Turf" was added to the Angry Birds Friends Facebook version and it was also added to the original "Angry Birds". In July 2012, the episode "Pigini Beach" was added to the Angry Birds Friends Facebook version. In August 2012, Rovio announced a partnership with the punk band Green Day, which led to 20 new levels of Angry Birds Friends on Facebook featuring all three members of the band. The