From photography to warfare, conservation to whistleblowing, this year’s five Oscar nominated documentaries are united by overlapping themes and topics of interest, but remain uniformly distinct in their approach.

Leading the quintet is Laura Poitras’ “Citizenfour,” the highest-grossing and highest-profile nominee. The verite-style portrait of NSA whistleblower Edward Snowden gives audiences a voyeuristic peek inside Snowden’s week in Hong Kong when the information he leaked started going public, and shows the human side of a man who the media nearly turned into a myth.

The pic has cleaned up in Oscar precursors, garnering best doc wins from the Gotham and Intl. Documentary Assn. awards, the four top critics groups (New York, Los Angeles, London and National Society) and nominations from BAFTA and the Spirits. It also marks Poitras’ second Oscar nom. She was in contention in 2007 for “My Country, My Country” but lost to heavyweight “An Inconvenient Truth.”

If there’s an obvious choice to upset “Citizenfour,” it’s the quirky crowdpleaser “Finding Vivian Maier” by first-time filmmakers John Maloof and Charlie Siskel. They celebrate the life’s work of Vivian Maier, an amateur photographer whose striking candid portraits of everyday people found a surprisingly rabid following after coming to light when she passed away.

Unlike Poitras, who remains discreetly off camera in her conversations with Snowden, Maloof places himself front and center in the film in the style of Morgan Spurlock and Michael Moore. That approach doesn’t always curry favor with voters, but the subject matter squares with the category’s two most recent victors — “Searching for Sugar Man” and “Twenty Feet From Stardom” — which also championed unheralded artists.

Wim Wenders’ hauntingly beautiful “The Salt of the Earth” focuses on a different, and very much alive, shutterbug. The renowned Sebastiao Salgado reflects on his life and work, including profound portraits of human suffering and some of our planet’s most primeval landscapes. Wenders, a two-time Oscar doc nominee for “Pina” (2012) and “Buena Vista Social Club” (2000), made the film in collaboration with Salgado’s son Juliano Ribeiro Salgado.

Landing her first nomination after a decade and a half of documentary filmmaking, Rory Kennedy’s “Last Days in Vietnam” is perhaps the most conventionally assembled nominee but no less powerful for it. Mixing archival footage with talking head interviews, Kennedy unpacks the harrowing fall of Saigon, as American citizens are evacuated and scores of Vietnamese try to flee. The chronicle may resonate especially well with voters of a certain age, making it a strong dark-horse contender.

Finally, Orlando von Einsiedel’s “Virunga” is the only nominee to also land a corresponding PGA nod and has the backing of exec producer Leonardo DiCaprio. An urgent missive from eastern Congo, the pic shines a light on the titular national park, a refuge for endangered mountain gorillas, under attack from various forces.