Final answer:
Walter's strategy of writing reflections and thoughts in his notebook after reading about migratory birds is freewriting, used to process information and deepen understanding.
Step-by-step explanation:
In the scenario described, Walter is reflecting on what he learned after reading a text about the patterns of migratory birds. The reading strategy Walter employs as he writes in his notebook is freewriting. This strategy involves jotting down reflections and thoughts to better understand and process the information absorbed. Walter's use of this strategy is most closely aligned with the described method of engaging with the text extensively, including asking questions about the text, summarizing, and noting personal reactions and changes in understanding or skills. Through freewriting, Walter is likely developing his ideas about the patterns of migratory birds, how they affect him, and what implications they might have on broader concepts.