Ha Ha Tonka. Photo by Todd Roeth.

It's little surprise that the members of Ha Ha Tonka, hailing from the Ozarks, have a natural affinity for bluegrass.

"Anything we do, whether we're trying to cover an R.E.M. song or what have you, comes out sounding Ozark-ian," said frontman Brian Roberts in a phone interview last week. But on Death of a Decade, released in April, that influence on the band's indie rock is front-and-center with Brett Anderson's mandolin.

Roberts said the quartet, which will perform at RIBCO on Friday, aimed for "brighter, more hopeful sounds" on the album. And because Anderson had been playing lots of mandolin, "it just became the starting point for a lot songs. ... It's such a colorful, I daresay happy-sounding, instrument. It definitely has a bright sound about it that I think ... helped capture the type of vibe or mood that we were wanting on the songs."

That description misses the tonal and artistic expansiveness of the album. The mandolin drives opening track "Usual Suspects," and it's indeed an upbeat rocker. But elsewhere, the instrument brings shading or a counterpoint; on "Lonely Fortunes," the mandolin adds balance, emotional complexity, and ambiguity simply through its pregnant tone.