Length of Birds' Breeding Seasons

Publisher Website
Google Scholar
Abstract
Published sets of breeding records for birds from 35 locations throughout the world were used to examine the relationship between length of the breeding season and latitude, annual rainfall, and altitude. The length of the breeding season was estimated as the number of equally good months for breeding (EGM), calculated by using a derivative of the Shannon-Wiener diversity index. Sets of records came from a wide range of latitudes and levels of annual rainfall, but most records were from low altitudes. The EGM is negatively correlated with latitude, and it decreases by1 mo. for every 11.degree. increase in latitude. There is no evidence of a difference in the EGM between Australia and Africa, but, latitude for latitude, Australia and Africa have a mean EGM 1.9 mo. longer than elsewhere. The EGM of birds in arid and non-arid parts of Australia are of similar length, and birds of arid parts have quite well defined breeding seasons, particularly in southern (mid-latitude) regions.