Where did the warblers go?

North Jersey, it seems.

While roughly a third of the warblers and other bird species that breed in the United States have suffered declines, several top birders in Bergen and Passaic counties say there have been above-average sightings locally this spring.

At Garret Mountain in West Paterson, one of the top birding spots in the region, bird-watchers have reported seeing as many as 20 species of warblers per morning a few times this month.

Bruce McWhorter, who goes birding at Garret regularly, said the diversity of warblers has been higher than usual, although there are no more of them than last year.

“The one exceptional exception,” McWhorter said, “was a flock of thousands of white-throated sparrows that passed through about two weeks ago.”

Rob Fanning, a top birder at Garret and the Celery Farm Natural Area in Allendale, said: “This may possibly be the best overall year for warblers I can remember at the Celery Farm, and the migration is far from over.”

Fanning reported seeing an unusually wide variety of the tiny songbirds at the 107-acre natural area, with good numbers of birds that are scarce in the spring – including Nashville, Northern Parula, chestnut-sided and black-throated blue warblers.

Hugh Carola of the Hackensack Riverkeeper said that in the Meadowlands, “the migration was kind of straggly at first because of the long cold snap, but we’ve got some really good birds coming in now.”

But despite the bad weather so far, Patrick Scheuer, director of the New Jersey Audubon Society’s Lorrimer Sanctuary in Franklin Lakes, says: “We sure have had more variety this year, including a Cape May Warbler, a black-throated blue and a springtime red-breasted nuthatch.”

Over the weekend, top birders competed in the World Series of Birding, in which the objective is to identify as many species of birds anywhere in New Jersey within a 24-hour time frame. The American Bird Conservancy had designated Saturday as annual International Migratory Bird Day.

The advocacy group reports that more than a third of the 650 bird species that breed in the United States have declining populations, smaller ranges or are threatened by loss of habitat, climate change, pesticides, free-roaming cats and other factors.

“Warblers aren’t doing well,” said Steve Holmer, the group’s director of public relations. “There’s been a significant decline in many species.”

One bird that the conservancy has singled out for special concern is the cerulean warbler, which the group called a “flagship species for songbird declines.” Its numbers have dropped by up to 70 percent in the past four decades.

The bright blue-and-white warbler is a prized sighting in North Jersey because it is seen so rarely here, although New York State birders report that ceruleans have returned in ample numbers to their nesting sites near Bear Mountain State Park this spring.