Four details that develop the topic sentence are 1. The two eagles flying outside made the narrator leave the desk 2. The seagulls in the window looking for food distract the narrator 3. The St. Bernard dog approaching to be petted interrupts the narrator 4. The stiffness in the legs of the narrator makes the narrator go for a ride.
Step-by-step explanation:
In a paragraph, the topic sentence summarizes the general idea or point of the paragraph. In this paragraph, the topic sentence is expressed by "Keeping my mind on my writing is not easy when I stay at my grandmother's ocean-side cottage". Besides this, topic sentence are supported and explained through supporting details, which includes reasons, examples, evidence, etc.
In this context, supporting details include all reasons or situation that stops the narrator from focusing on writing. This means the supporting details include 1. the eagles flying outside as this causes the narrator "to leave my desk and rush to the doorway"; 2. the seagulls in the window because this causes a "confusion of sounds" that distracts the narrator; 3. the dog looking for attention in the narrator because this also, disrupts the process of writing, and 4. the stiffness in the legs of the narrator because this makes the narrator "spring onto my bike, and pedal off down the beach".