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 Action! from the app stores. Instead of using a slingshot like in the original "Angry Birds", the birds dash through an area in a top down perspective and ricochet like pinballs. Most levels have pinball-style bumpers and sometimes there are hazards such as TNT crates, rocks, blocks of ice or strong winds. Each Angry Bird has a different ability, such as Bomb's ability to blast obstacles near him and Chuck's speed boost, which allows him to fly against powerful fans. Players have a limited number of birds to use for completing each level, and each bird has enough stamina to be