Final answer:
The increase in the female cowbird's hippocampus size during the breeding season is most likely due to hormonal changes associated with the environmental demands of remembering multiple spatial locations for nesting.
Step-by-step explanation:
The student's question relates to the study of how the female cowbird's hippocampus increases in size during the breeding season. This phenomenon can be linked to the hormonal changes that occur in response to the need for remembering multiple spatial locations.
It is known from previous studies that steroid hormones induce dendritic plasticity, which affects the structure of neurons in areas of the brain involved in memory and learning, such as the hippocampus. During estrus cycles, variations in estrogen were found to correlate with changes in the hippocampus structure. Certain environmental factors, such as the ones included in chronic unpredictable mild stress (CUMS) protocols, can induce physiological changes in animals, which can also lead to adaptations in brain structures and functions. Therefore, hormonal changes related to the environmental demands of breeding season may cause the increase in hippocampus size in female cowbirds.