Playing Dead
Anytime there's "Death" in the title, it's worth paying attention to. What does death make you think of? Dead people? Tombstones? Grief? Loss? Zombies? Here Heaney pulls a fast one on us. No one actually dies in this poem. While the word death pulls us in and puts us on the edge of our seats before we even begin the poem, the death in this one is figurative, not literal. No need to bust out your black funeral attire, but we are as readers prepared for the idea of loss from the get-go.
Nature is a Two-Headed Muppet Monster
Well, not really, but in the case of this poem, "naturalist" has two definitions. The first, which applies directly to the meaning of the poem, is someone who is an expert in natural things, particularly zoology (think frogs) or botany. You know the type—all khaki safari wear and field guides bursting from a well-worn satchel. The speaker, who seems to be a budding naturalist, with a keen interest in the flax dam and frogs, "dies" (or his interest dies) at the end of the poem, when he sees the horrifying scene of the frogs slapping around in a threatening and disgusting way.
The second definition of "naturalist" is the adherence to naturalism in art. This definition applies more to the poet than to the poem. If you've ever read any of Heaney's other poetry, you'd know nature plays a big role, and by big we mean like the size of a thousand-year-old redwood. But maybe he's making a statement that although nature plays a big role in his poems, he doesn't consider himself a naturalist poet. There's nothing like "killing" the (naturalist) character off the show to shake things up. Amirite, Game of Thrones?
At the end of the day (or the froggy life cycle), the title alerts us to a profound change. However you want to interpret the titular "Death" of the title, we understand that this poem is about growing older, and what gets life behind in the process.