In children’s picture books, true collaborations between authors and illustrators are uncommon. But Hatfield, Massachusetts, author Jane Yolen and Easthampton illustrator Bob Marstall are two old friends. Their work together on the picture book On Bird Hill all began with a doodle.

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Click the video player below to see the illustrations and hear Marstall and Yolen talk about the birth of the book and working together. At the end, they read the whole book.