Growth and morphology of nestling Hooded crows Corvus corone cornix, a sexually dimorphic bird species

Abstract

The growth and morphology of nestling Hooded crows, Corvus corone cornix, were studied at Trondheim, Central Norway, during 1980 and 1981. The sexual size dimorphism of the nestlings developed while they were in the nest, but was less pronounced than that of the juvenile birds. Female young grew relatively faster than the males. The size variation of the morphological characters studied was greater in the males than in the females, during the entire nestling period. The order of development of the different morphological characters seemed to be adapted to the needs of the nestlings during the nestling period. Growth of the bone and bill characters was the highest priority, body weight and feather characters the lowest. In general, the sizes of the different morphological characters were highly intercorrelated, particularly those that developed at the same time during the growth period. In the favourable breeding season of 1981, the nestlings were larger than in the unfavourable season of 1980. The high priority characters of the males increased more in size than did those of the females, and the low priority characters of the females increased more in size than did those of the males. About 75% of the nestlings could be correctly sexed from their external morphological characteristics. The findings support the view that the parental cost of rearing a male offspring is greater than that of a female.