The Naturalist offers a charming glimpse into the woodland life of one of his most enthusiastic little adventurers. The painting captures a mouse paused mid-expedition on the forest floor, dressed in the manner of a Victorian field naturalist and caught in the very moment of looking up from his work, his bright eyes meeting the viewer's gaze with an expression that is at once slightly startled and unmistakably inquisitive, as though we have interrupted him in the middle of cataloguing some important discovery. Walker's title here is a beautifully apt one. The Naturalist conjures up the great tradition of British nature study, the world of Gilbert White, the country parson with his notebook, the gentleman scholar with his butterfly net and specimen jar. Pairing the title with a mouse, the smallest and most overlooked of woodland creatures, gives the painting its gentle comic charge, the entire grand tradition of natural history scaled down to fit a creature who is himself part of the very world he so diligently studies.

The mouse is dressed for serious fieldwork, wearing a soft sage green jacket with a crisp white collar and a bright red ribbon tied neatly at the throat, the kind of considered ensemble that suggests a gentleman who takes his pursuits seriously. His head is tipped attentively upward, large rounded ears alert and whiskers fanning out as he engages the viewer directly, the open pages of his field notebook still clasped in his small paws as though he might return to them at any moment. A satchel is slung over his shoulder, ready to receive whatever treasures the day's foraging might yield, and he leans casually against the cap of a woodland toadstool that serves as both resting post and field desk. His long pink tail trails out behind him across the woodland floor, lending the figure a wonderful sense of movement and presence. The setting is unmistakably that of an English wood in autumn, the ground a rich tapestry of fallen leaves, acorns and tangled undergrowth painted in deep russets, ochres and burnt umbers, while behind him the trunks of trees rise softly into a misty wash of blues, mauves and pale yellows, suggesting the dappled light of a woodland clearing.