It looks like the biggest of the food chain might be the most vulnerable. The National Geographic special “Whales in Crisis” (7 p.m., PBS) follows a new generation of whale watchers who all see dangers for Earth’s largest mammal.

Marine biologist Ken Balcomb has been monitoring generations of whales from his observation station on Washington state’s Puget Sound. He’s recently noticed many whales dying or disappearing long before their time. Last May, he watched several whales behaving erratically, racing toward shore and certain death. It appears that they were literally driven mad by the sonar from a nearby Navy destroyer. Balcomb believes that sonar may be the reason for many whale fatalities.

Not all of these whale tales are so blue. The Arctic’s great bowhead whale was once the prize of European whalers and was recently on the verge of extinction. Limitation on whaling has brought them back from the brink. Scientists now think some bowheads may live as long as 200 years.

• After the votes are tallied on “American Idol” (7:30 p.m., Fox), only nine contestants will remain. While it’s clear that La Toya London and Fantasia Barrino remain the voices to beat, there are a few Idols I won’t miss. The judges seem to adore the mellow Hawaiian Camile Velasco, but I was hardly surprised to see her end up among the bottom three last week. She always performs like she’s just gotten out of bed.

Tonight’s other highlights

• Scheduled on “60 Minutes II” (7 p.m., CBS): an American soldier accused of cowardice; heart transplants; terror and mass transit.
• Willie Nelson and Gary Busey saddle up in the 1982 western “Barbarosa” (7 p.m., AMC).
• A documentary crew captures more than they expected on “The West Wing” (8 p.m., NBC).
• “The New Americans” (8 p.m., PBS) continues.
• Scheduled on “48 Hours Investigates” (9 p.m., CBS): three juvenile offenders who committed atrocious crimes whose sentences are due to expire.
• McCoy receives bad news about an old colleague on “Law & Order” (9 p.m., NBC).
• Evil appears to be getting the upper hand on “Kingdom Hospital” (9 p.m., ABC).

Late night

Johnny Knoxville appears on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno welcomes David Arquette and Blue Man Group on “The Tonight Show” (10:35 p.m., NBC).

Minnie Driver, Chris Klein and Usher are scheduled on “Late Night with Conan O’Brien” (11:35 p.m., NBC) … Roseanne and Greg Proops appear on “The Late, Late Show with Craig Kilborn” (11:37 p.m., CBS).