It’s about 15 minutes before sunrise, and we’re standing in the middle of a marsh listening for a bird call that sounds like TV static. The call belongs to the endangered California Ridgway’s rail, a plucky but shy marsh-dwelling bird. The rails are both the heroes and antagonists of a conservation paradox that’s unfolding here in the San Francisco Bay.

The ecologists we’re shadowing are trying to save the birds, but they’re also trying to eradicate the invasive grass that the birds have come to rely on. And that forces a tricky question: what if, in order to save an endangered species, we actually have to preserve an invasive one?

No one really wants the grass, called hybrid Spartina, anywhere near the bay. Our interview subjects certainly don’t: they work for the Invasive Spartina Project, an entire organization dedicated to the plant’s removal. The hyper-aggressive grass crowds out native species, and eats up acre upon acre of tidal mudflat that countless migrating shorebirds desperately need. The eradication effort has been in full swing for more than 10 years, and while they’ve wiped out about 95 percent of the invading grass, that last 5 percent is full of endangered rails who thrive in it.

The story is quirky, but the questions it raises are big. What do we do when an invasive species starts to do some good in an ecosystem? How much money and time should we spend fighting off an invader, or saving a threatened species, or both? And what happens when we hit a stalemate like this one? Check out the video above to wade into the debate, and to decide for yourself about that bird call.