The birds will fly over Pittsburgh while migrating.By Royce Jones

PITTSBURGH (KDKA) — If you see a bunch of birds swarming the sky Monday night, don’t be alarmed. The Pennsylvania Natural Heritage Program said this is part of a massive fall migration flying south.

According to a BirdCast prediction, more than 400 million nocturnal birds will migrate across the country overnight. There are 19,000 expected to fly over the City of Pittsburgh.

Monday night, the southern-bound birds will fly red-eye from the north. They are flapping from all over in their ordinary fall migration.

“In a pie piece that extends from Nova Scotia to Alaska,” said Robert Mulvihill, an ornithologist with the National Aviary.

Pittsburgh is under a high migration watch. But why so many birds? Ornithologists believe bad weather delayed the flight.

“Maybes the conditions weren’t ideal for a period of several days or a week or more,” Mulvihill said.

Passing overhead will mostly be warblers and passerines, experts told KDKA.

To hear them, experts said your best shot is to run outside right before sunrise and listen for their bird call. Seeing them won’t be so easy because it will be dark.

But Pittsburgh is considered a popular rest stop for birds, because of our heavy trees and abundant wildlife. So you might spot them while they refuel.

“You should have a chance to see dozens of kinds of birds. And hundreds of individual birds,” said Mulvihill.

The birds have an already-high flight risk as they are heading south towards tropical storms. So before bed, the National Audubon Society said flip off your light switches.

“So that they won’t bang into these buildings and get confused as to where they’re going,” said Katharine Dodge with the Audubon Society.

Artificial light confuses the birds.

You can submit your bird observations online through e-bird to help scientists make future migration predictions.