Some of the birds have already started leaving.

They have lifted off and headed for the Arctic, where they need to mate, breed, and get out quickly, before the early snows start.

And shorebird scientists who have spent the month of May on Delaware Bay studying the birds -- in particular, one on steep decline called the red knot -- are relieved.

This year, they estimated that 26,000 red knots were on the bay, a number to equal last year, which was the highest they've seen in years.

Red knots had once numbered as many as 100,000 birds on the bay.  But they began declining in the 1990s, and biologists eventually blamed an aggressive harvest of horseshoe crabs, whose eggs the birds feed on to regain their weight and strength during the migration from the tip of South America.

Harvest restrictions were put in place, and now, the birds appear to be recovering, although that's always iffy, the biologists say. (Horseshoe crabs are used as bait in the whelk and eel harvest. In a previous post, I wrote about an announcement Wednesday that researchers had come up with an artificial bait that could relieve the harvest pressure on the crabs.)

"Pleased" is how shorebird researcher Larry Niles, who has followed these birds to the ends of the earth to study them, described his reaction. He and Amanda Dey of the New Jersey Department of Environmental Protection's Endangered and Nongame Species Program, which Niles formerly headed, lead a team of international researchers on the bay each May, when the birds are there.

Counting 26,000 birds requires considerable expertise -- researchers have a technique that involves counting a group, and then multiplying -- and Niles said this year's count corroborates last year's. He said the good news speaks to the management that conservation groups, agencies and others are involved in.

This year, the situation was iffy -- not because of the crabs, but because of the bay's beaches, many of which were washed away in Superstorm Sandy last fall. The crabs need the beaches to lay their eggs on, and the birds need the eggs.

But a last-minute push resulted in roughly $1 million in grants and funding, and regulators came through with permits. The beaches were replenished.

"We averted the disaster that could have happened," Niles said.

Better yet, during a three-day storm with northwest winds, the beaches held.

And of the 26,000 red knots, all but about 1,000 were on the New Jersey side of the bay. The rest were on the Delaware side. Clearly, the birds' vote is in.

In replenishing the beaches, "we targeted making beaches expressly for horeshoe crab use," Niles said. "We learned more about how to make good crab habitat."

Now, "we're hoping to charge ahead and restore morebeaches this year," Niles said.  "It taught us that it's possible. It also taught us that birds respond.  It's the thing we can do."

Meanwhile, an update on B95, the celebrated oldster that was spotted several times on the beaches, hasn't been seen for a week.

Nicknamed the Moonbird because in his 20 years, he has probably flown the equivalent distance of to the moon and back, he probably came early, ate heartily and took off already, Niles figures.

"I think he left."

Will they see him again? Or will it be what they always tell themselves: No bird lives forever.

Wait and see.