MIAMI — The grasshopper sparrow, a tiny Florida prairie bird perched on the verge of extinction for the last decade, may have encountered a final, unconquerable foe: an invasive new disease quickly killing off its young.

The disease has spread so rapidly that wildlife managers now fear another endangered sparrow, the Cape Sable seaside sparrow in the Everglades, could also be at risk if numbers fall any lower.

“Extinction is a real possibility,” for the grasshopper sparrow, said Larry Williams, the U.S. Fish and Wildlife Service’s Florida supervisor for ecological services. “We are very anxious to know what these diseases are, and how they’re operating.”

Another threat is also at play: money. The Service has so far spent $1 million on conservation efforts, including a captive breeding program, aided by private donations. Williams said the agency has requested another $150,000 to $200,000 for the coming year, but “budget uncertainties” remain. And with nesting season starting in May, time may be running out.

“2018 is really the do or die year for the grasshopper sparrow,” said Paul Reillo, president of the Rare Species Conservatory Foundation in Palm Beach County, where the first captive sparrow was bred two years ago and which has set up a matching grant fund drive with Florida International University’s Tropical Conservation Institute. “The facilities need to be built now so we can apply our best effort this season to ensure the birds are given their very best chance.”

The Fish and Wildlife Foundation of Florida has also set up an emergency fund, which Williams said has so far raised $12,000.

With the number of the wild birds expected to total less than 40 this year, the grasshopper sparrow, which lives only in shrinking swathes of prairie in Central Florida, could well become another sad chapter in the state’s foundering effort to save its prairie sparrows.

Eight species of prairie or seaside sparrows once darted across Florida’s rolling marshes and dry prairies, shy golf-ball sized ground dwellers perfectly feathered to disappear and nest in the tall grasses. Being so earthbound made them vulnerable to predators, like snakes and invasive fire ants, flooding during heavy rains, and parasites in the soil they foraged for bugs. But their biggest threat turned out to be development, with nearly all their habitat paved over or altered for flood control.

Two birds, the Smyrna and dusky seaside sparrow, vanished by 1987 as their habitat disappeared. Two others are in decline. And two, the grasshopper and Cape Sable, now face what wildlife managers call the extinction vortex – an unstoppable downward spiral reached when populations drop to such low numbers that threats like disease and shrinking habitat become mutually reinforcing.

“That tells us we can’t let populations get below certain thresholds,” Williams said.