. British birds. Birds. OTES. ON THE CROSSING OF THE BILL OF THE CROSSBILL. It has long been known that, in the Common Crossbill {Loxia curvirostra) the mandibles cross indifferently on either side in different individuals. Recently, however, for a special purpose, I desired to ascertain whether or not individuals having the mandibles crossed to the right and to the left, respectively, exist in nature in about equal numbers, and (if not) what proportion of individuals has them crossed to the right and what to the left. Hitherto, this point has not been investigated, so far as I am aware. Accor
. British birds. Birds. OTES. ON THE CROSSING OF THE BILL OF THE CROSSBILL. It has long been known that, in the Common Crossbill {Loxia curvirostra) the mandibles cross indifferently on either side in different individuals. Recently, however, for a special purpose, I desired to ascertain whether or not individuals having the mandibles crossed to the right and to the left, respectively, exist in nature in about equal numbers, and (if not) what proportion of individuals has them crossed to the right and what to the left. Hitherto, this point has not been investigated, so far as I am aware. Accordingly, at the British Museum (where they have a very extensive series of Crossbills), I examined the contents of ten boxes, selected at random. These contained altogether one hundred and seventy-one specimens, of all sexes, colours, and ages (other than nestlings), coming from all parts of the world to which the bird is indigenous. The result of my investigation was that there were eighty- four specimens which were dextral, eighty-three which were sinistral, and four which were doubtful. By a " dextral " specimen, I mean one having the upper mandible crossing the lower to the bird's right side (that is, to the left side of an observer facing the bird); and by a " sinistral " specimen, one having the upper mandible crossing the lower to the bird's left side (that is, to the right side of an observer facing the bird). Such close equality in the numbers of the two forms is quite surprising. If the proportions of the two forms observable in these particular specimens are fairly typical of the proportions which obtain in nature (and I saw no reason to doubt that they were), it appears that the two forms exist in astonishingly equal numbers.* * There must surely have been some error of observation in con- nexion with the statement (Mag. of Nat. Hist., 2nd ser., I., p. 165 : 1837), by my old friend the late Mr. Joseph Clarke, , of Saffron Walden, that "
Size: 1471px × 1698px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherl, booksubjectbirds
