FAMILY STRIGIDAE 1 85 



lighter, brighter brown, and has the toes somewhat more extensively 

 feathered. A. r. tacanensis Moore from Chiapas, known only from 

 the type specimen, is said to differ in short, buffy streaks on the fore- 

 head. Another form, based on a single specimen taken in Oaxaca, has 

 been named Aegolius acadicus brodkorbi by Marjory A. Brooks 

 (Proc. Biol. Soc. Washington, vol. 67, 1954, p. 180). This resembles 

 those known from farther south, but has light markings, restricted in 

 extent, on the primaries and the tail. In this it shows approach to the 

 immature stage of acadicus. Miss Brooks, in connection with her 

 description, points out a similarity in these birds in their apparent 

 retention through life of a plumage stage found only in the immature 

 of the generally similar populations of the north to a condition found 

 in certain salamanders. These regularly reproduce in a stage similar 

 to the larval form of related kinds. Some of them on occasion may 

 develop adult body form, a change that may be instigated artificially 

 through thyroid stimulation. Her interesting suggestion is that persis- 

 tence among saw- whet owls resident in the south of a plumage 

 similar to that of the immature in the birds of the north may represent 

 a neotenic stage similar to that of the salamanders. On this reasoning 

 she regards all of the owls under discussion as races of Aegolius 

 acadicus. 



