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
Stymphalian birds Stymphalian birds The Stymphalian birds ( ; , "Stymphalídes órnithes") are a group of voracious birds in Greek mythology. The birds' appellation is derived from their dwelling in a swamp in Stymphalia. The Stymphalian Birds are man-eating birds with beaks of bronze, sharp metallic feathers they could launch at their victims, and poisonous dung. These birds were pets of Artemis, the goddess of the hunt or have been brought up by Ares. They migrated to a marsh in Arcadia to escape a pack of wolves. There they bred quickly and swarmed over the countryside, destroying crops, fruit trees, and townspeople.