A region of the canary forebrain shrinks during the nonbreeding season and enlarges when breeding season begins. This change is probably associated with the annual a. addition of new syllables to a canary's song repertoire. b. crystallization of subsong into adult songs. c. sensitive period in which canary parents imprint on new offspring. d. elimination of the memorized template for songs sung the previous year.

Verified step by step guidance

1. Identify the key biological concept: The question revolves around the changes in the canary forebrain in relation to its breeding behavior and song patterns.
2. Understand the options: Each option suggests a different aspect of song behavior in canaries, which might be linked to the changes in the forebrain size.
3. Relate forebrain function to song behavior: The forebrain in birds is known to be involved in song learning and memory. An increase in size could indicate enhanced activity or capacity related to these functions.
4. Analyze the options in relation to forebrain function: Option (a) suggests the addition of new syllables, which implies learning new songs or modifying existing ones, likely requiring enhanced brain activity or capacity.
5. Conclude the most likely answer: Since the forebrain is involved in song learning and memory, and its enlargement coincides with the breeding season when new songs might be learned or existing ones modified to attract mates, option (a) is the most plausible answer.