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 biological phenomenon described: The canary forebrain changes size seasonally, shrinking during the nonbreeding season and enlarging during the breeding season.
2. Consider the functions of the forebrain in birds, particularly in relation to song production and learning, which are crucial during the breeding season.
3. Evaluate each option provided in the context of the forebrain's role: a) addition of new syllables, b) crystallization of subsong, c) imprinting on offspring, d) elimination of memorized song templates.
4. Understand that the enlargement of the forebrain during the breeding season is likely linked to increased neural activity related to song learning and production, which is essential for attracting mates.
5. Conclude that the most plausible explanation for the forebrain's seasonal change is related to the addition of new syllables to the canary's song repertoire, as this requires neural adaptation and growth.

Key Concepts

Neuroplasticity

Neuroplasticity refers to the brain's ability to change and adapt in response to experience, environment, or learning. In canaries, this concept is crucial as it explains how the forebrain can shrink or enlarge based on seasonal changes, allowing for modifications in song patterns during breeding seasons.

Song Learning in Birds

Song learning in birds involves the acquisition and modification of vocalizations, often influenced by social and environmental factors. Canaries exhibit changes in their song repertoire, adding new syllables or refining existing ones, which is linked to the structural changes in their forebrain during breeding seasons.

Sensitive Periods

Sensitive periods are specific times during an organism's development when it is particularly receptive to certain environmental stimuli. For canaries, these periods may coincide with breeding seasons, allowing them to imprint on new songs or offspring, which could be related to the observed changes in brain structure.