Width Of Foramen Magnum Research Articles

Morphology of the Hooded crow Corvus corone cornix in relation to age, sex and latitude

The morphological variation of the Hooded crow at Trondheim, Norway, was studied, based on a sample of 734 birds collected during a six year period. Mouth colour, plumage colour, skull thickness and feather length were found to be characters which could readily be used to separate juveniles from adults. Females aged 15–19 months had a thinner skull roof than older female birds. Low coefficients of variation were found for the lengths of the third primary and of the tail feathers. A discriminant analysis showed that of the various body dimensions studied bill height and bill length distinguished the sexes most precisely. A high degree of sexual dimorphism was also found to exist in body weight and in the thickness of the skull roof.Those body structures which develop at about the same stage during the juvenile growth period were associated with the same principal component, viz. the lengths of bony structures, parts that develop early on in life, were intercorrelated (wing bones, tarsus, bill basis and the width of foramen magnum). The lengths of the primaries and of tail feathers were also intercorrelated, structures which develop late.The mean body weight of the Hooded crow population studied in Norway was intermediate between that of the Hooded crow in Germany and of the Carrion and Hooded crows in England and Scotland. No such differences were found in wing length. Norwegian Hooded crows have shorter tails than German ones, but their bills are much larger, in particular for the females. Therefore, the degree of sexual dimorphism in bill size seems to be reduced at high latitudes.

Variation in the long-tailed field-mouse (Apodemus sylvaticus (L>)) in the Channel Islands.

Measurements of ten skull characters were made on each of 352 specimens ofApodemus sylvaticus(L.) and 37 specimens ofA. flavicollis(Melch.). The latter were obtained from southern England and the former from five of the Channel Islands, two localities in southern England and one in northern France. The characters were greatest length, greatest width, interorbital breadth, cranial breadth, width of foramen magnum, length of maxillary tooth row, length of palatal foramen, distance between ventro-posterior processes of pterygoids, length of mesopterygoid fossa and minimum distance between first upper molars. The ages of the skulls were ascertained by means of a tooth-wear measurement. A regression adjustment was used to bring all the characters to a uniform age class. The sexes were separate throughout the analyses. The unadjusted and adjusted means have been calculated of each character for every locality. Appreciable variation occurs between the populations examined, with the females slightly smaller than the males but following the same general pattern of variation. An analysis into canonical variates was made with a view to accounting for the largest possible part of the variation between groups using a limited number of linear combinations of the original measurements. Almost all the variance was contained in the first four canonical variates and from these it appeared that the populations separated into three groups. The first contained the mainland mice from Hampshire, Cornwall and Cap Gris Nez, the second those from the Channel Islands and the third the collection ofA. flavicollis.The analysis confirms that in the British IslesA. flavicollisis distinct fromA. sylvaticusand that the Channel Island mice, although larger than the mainlandA. sylvaticus, probably belong to that species. Differences between populations from the Channel Islands are small, although the mice from Herm and Sark are relatively large. It is possible that the Channel Island mice could have been derived from a common stock.