Oklahoma has 14 endangered species that are either native or migrate to the state.
One of them nests in Tulsa along the Arkansas River.
The Interior Least Tern flies to Oklahoma from the Caribbean and South America every spring.
In recent years, they've thrived in Green Country, but that could be changing.
Tonya Dunn with the Army Corps of Engineers has been observing the terns for seven years.
And when she went to check on them after the Fourth of July, they were all gone.
Zink Island is one of their main nesting habitats here in Oklahoma.
It's a bald, man-made rock island in the middle of the Arkansas River, near 21st Street and Riverside Drive.
A couple weeks ago, there were dozens of adults and chicks. But yesterday, there weren't any the island.
Dunn says there's no telling what happened -- she doesn't think it's human disturbance --- the fireworks could have spooked them, or maybe birds of prey raided the nests.
She said she hopes they can re-nest in Tulsa before they fly back for the winter.
Kevin Stubbs with the U.S. Department of Fish and Wildlife also observes the terns, and he said a proposed dam project on the river could also affect the birds.
Part of Zink Island will go underwater if the design changes at the dam raise the water level. But we're going to make up for it by building up some other habitat just downstream of the dam.
About a year ago, people from nearby apartments were hitting golf balls onto the island.
The fines for intentionally killing endangered species, or disturbing their habitat, can be up to $100,000 and even jail time.