Rectrices

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A rectrix (plural: rectrices) is a type of vaned flight feather in the tail of most modern birds and possibly some species of maniraptoran dinosaurs. Rectrices are a type of pennaceous feather. They form a single transverse row of quills on the margin of the anatomical tail. The rectrices are absent in grebes and some ratites and greatly reduced in penguins.

The rectrices are paired and their number is almost always constant within a sex, species and sometimes even throughout a whole order, six pairs being most frequent. This number is found throughout the family of Passeriformes, with few exceptions. Trogoniformes and Strigiformes also generally have six. Ostriches have the highest recorded count, at 25 to 30 pairs. In domestic pigeons - which all belong to the same species -, the number of rectrices is highly variable due to selective breeding; in some grouse, a varable number of rectrices is found to occur naturally.