Seven pelicans returned to the waters north of downtown St. Petersburg after recovering from an illness that killed about 60 birds in the same rookery.
The cause of the illness remains a mystery.
The die-off began around Coffee Pot Bayou about two weeks ago. Some pelicans were found paralyzed.
The Florida Fish and Wildlife Conservation Commission is investigating the cause along with scientists hired by St. Petersburg.
City spokesman Bill Logan says the source could have been dying fish in a retention pond near Riviera Bay.
"Once the birds ate some of those fish that may not have been dead but were compromised or sick that could have introduced another toxin, that seems to be the prevailing wisdom at this point," Logan said.
The fish were being killed by low oxygen levels caused by a cold snap.
Logan says scientists don’t believe the millions of gallons of sewage released into Tampa Bay during Hurricane Hermine were a cause. Water samples taken around the rookery came back clean.