442 



PICARIAN' BIRDS 



of being protruded a great distance ; — an arrangement rendered possible 

 by the peculiar structure of its supporting bones, which curl round the 

 back of the skull. It is, however, interesting to note that in a few 

 foreign woodpeckers the structure of the tongue is normal, thus showing 

 that the specialisation in the more typical kinds is a feature which has 

 been evolved in accordance with special needs. Unlike perching-birds, 

 woodpeckers and wrynecks have the oil-gland tufted ; and they are 

 further characterised by having two notches on each side of the lower 



or hind border of the 

 breast-bone ; by the 

 absence or rudiment- 

 ary condition of the 

 pair of blind append- 

 ages (ccuca) to the in- 

 testine ; and by the 

 spinal feather- tract 

 being well defined on 

 the back, on the lower 

 part of which it forms 

 a fork. Although the 

 outermost pair is 

 often short and con- 

 cealed b}' the coverts, 

 these birds have 

 twelve tail-feathers. 

 As a rule, the beak 

 is strong and conical, 

 with the upper half 

 chisel-like in shape, and thus admirabh' adapted for cutting awa}- the 

 wood of half-rotten tree-trunks. 



The t\'pical woodpeckers, constituting the subfamily Picina:, arc 

 characterised by the stiff shafts to their tail-feathers, the tips of which 

 arc pressed against the bark of the trees when the birds are climbing 

 or boring. In consequence of the severe usage to which these feathers 

 are subjected, the tail frequently becomes much worn, so that its length 

 varies in different individuals of the same species. When on the wing, 

 these birds may be recognised by their peculiar undulating flight ; and 

 when on trees they nearly alwa\-s cling to the stem, instead of perching, 

 with the head upwards and the tail closely pressed to the bark. As a 

 rule, they ascend and descend in diagonal lines ; and all the European 

 species drill holes in the stems or boughs for the reception of their pure 



GK K.KN WOODI'KCKKK . 



