This is not gonna fly!

Migratory birds keep smacking into a glass railing at the World Trade Center’s elevated park and dying, according to wildlife advocates.

Dozens of songbirds have crashed into the roughly 300-foot-long, see-through barrier in Manhattan’s Liberty Park —  white-throated sparrows, juncos and hummingbirds among them — and been found dead in recent weeks, wildlife rehabilitator Beverly Mastropolo told The Post.

“Because the glass reflects the sky and trees, birds think they have a clear path through the glass and smash into it with their fragile beaks and heads,” she said in an email.

“Even if the impact doesn’t kill a bird immediately, it may be injured or stunned when they fall.”

The 3-foot railing, which sits roughly 25 feet above a pedestrian walkway, is an obstacle for birds as they soar west towards the Hudson River.

On Wednesday, two birds were lying dead near the railing — ruffling parkgoers’ feathers.

“How terrible!” crowed Juliette Rosa, 22, a tourist from Costa Rica. “Oh, the poor little things!”

Others said a reflective glass building nearby, 4 World Trade Center, is also a glimmering hazard for their feathered friends.

“That’s sad,” said Brandon Mullins, 51, who works in the area and eats lunch in the park. “Must happen a lot in the city.”

Indeed, up to 230,000 migratory birds are killed in collisions with building glass each year, according to an NYC Audubon report.

Other birds that have croaked due to the railing include common yellowthroats and ovenbirds, which often fall into the pathway or street below, Mastropolo said.

Wildlife advocates want the clear glass railing panels replaced with tinted ones — or to add collision stickers — to deter birds from the site, which overlooks the National September 11 Memorial & Museum in Battery Park City.

A rep for the Port Authority of New York and New Jersey, which runs the park, said it’s investigating the cause of the bird fatalities.

“We’re looking into the matter,” said PANYNJ spokeswoman Amber Greene.