The "lights out" project - organised by NYC Audubon - runs until 1 November, when migratory birds are expected to have completed their autumn migrations.
The Empire State and Chrysler buildings are among those dimming their lights.
An estimated 90,000 birds each year are killed in the city as a result of striking glass-fronted buildings.
Organisers of the annual initiative, now in its fifth year, say the bright lights disorientate the migrating birds and override their natural navigational cues.
