According to poll figures I just made up, 73 percent of homeowners are obsessed about keeping squirrels out of their bird feeders and keeping deer from eating their vegetables, flowers and shrubs. Tonight’s “Nature” (7 p.m., PBS) will shed no light on the eternal battle between man and squirrel, but “The Private Life of Deer” is illuminating.

According to “Private Life,” there are more than 30 million white-tailed deer in the United States. That’s up from fewer than a million a century ago. We’re told that they rank among the most studied of all wild creatures. So how come most of us can share our backyards with deer and yet know so little about them? Where do they sleep? And when? When is their feeding time and how long does it take to digest a whole flowerbed?

”Private Life” uses modern technology, including GPS tracking devices and night vision photography, to paint a picture of the deer as an affectionate and highly social creature. This portrait may soften the hearts of gardeners who’ve come to see it only as an azalea-eating parasite and a car repairman’s best friend.

• “Secrets of the Dead” (9 p.m., PBS) examines “Death on the Railroad,” a 19th-century mystery about the deaths of 57 Irish immigrants who all expired within months of arriving on these shores.

Tonight’s other highlights:

• The competition continues on “The Voice” (8 p.m., NBC) and “American Idol” (7 p.m., Fox).

• Malcolm has business to settle with the seismologist on “Arrow” (7 p.m., CW).

• A sniper strikes on “Law & Order: Special Victims Unit” (8 p.m., NBC).

• A skating rink inspires some juvenile behavior on “Modern Family” (8 p.m., ABC).

• “MythBusters” (8 p.m., Discovery) tests questions from the cast of “Deadliest Catch.”

• A fake ghost hunter becomes a real corpse on “CSI” (9 p.m., CBS).

• Severide faces charges on “Chicago Fire” (9 p.m., NBC).

• Juliette and Rayna compete for CMA Awards on “Nashville” (9 p.m., ABC).

• Kal Penn hosts “The Big Brain Theory: Pure Genius” (9 p.m., Discovery).

• A bumbling Gus mistakenly implicates himself in a murder on “Psych” (9 p.m., USA).