“Nature” (7 p.m., PBS, check local listings) puts on a really big show, devoting three hours to the life, death and procreation of the planet’s most enormous creatures. “Ocean Giants” literally spans the globe, traveling from the Arctic to the Amazon to capture whales at their most amorous, murderous and mysterious.

Caution: The first hour of “Giant Lives” includes some frank depictions of whale intimacy. After an hour of whale love and death, “Nature” proceeds to “Deep Thinkers,” a look at the cognitive and even emotional lives of whales and dolphins, mammals with rather large brains. “Nature” concludes with “Voices of the Sea,” an exploration of our dim understanding of undersea mammal communication. Humpback whales not only sing but also travel and gather to form “choruses.” Other whales hunt and travel in groups using complex clicks and sounds that may represent a code-like language. We don’t know what they’re saying, but this three-hour “Nature” will give us plenty to think and talk about.

• “American Weed” (9 p.m., National Geographic) follows marijuana cultivators in Colorado, where it is legal to grow and reap profits from harvesting medicinal cannabis. Following on the heels of Discovery’s “Weed Wars,” this marks a cable trend of sorts, perhaps one to spark more conversation and legislation about national marijuana policy.

• A painter puts her career on hold to raise her mentally impaired sister in the 2011 documentary “Raising Renee” (7 p.m., HBO2).

Tonight’s other highlights

• An overheard conversation rattles Phil on “Modern Family” (8 p.m., ABC).

• “Ghost Hunters International” (8 p.m., Syfy) opens a new season in Peru.

• A house vanishes on “CSI” (9 p.m., CBS).

• Classifieds can be murder on “Law & Order: Special Victims Unit” (9 p.m., NBC).

• “20/20” (9 p.m., ABC) offers “Before They Were Famous” glances at Oscar hopefuls. This is news?

• Jack’s (Tom Cavanagh) illness puts Hank to the test on the season finale of “Royal Pains” (9 p.m., USA).