The term 'MOTHER PTARMIGAN' is composed of two words, the first being 'MOTHER' which is a 3 letter word meaning a female parent, and the second being 'PTARMIGAN' which is a type of grouse bird native to the Arctic tundra. The crossword solution for 'MOTHER' is 'HEN', which is another word for a female bird. Therefore, the crossword solution for 'MOTHER PTARMIGAN' is 'HEN', which is a fitting answer as it refers to the female parent of the PTARMIGAN species.