Police say they are investigating reports that a man has been stealing ducklings and goslings before selling them online.
Officers from GMP Chadderton are stepping up patrols near the Salmon Field fishing lake in Royton in response.
The force say they received reports that a male had been attempting to sell the baby birds on Facebook and Gumtree.
An investigation has been launched.
Local residents posted on social media to say they had also noticed a number of baby ducklings missing from Foxdenton Park in Chadderton.
The Royal Society for the Protection of Birds (RSPB) have also been notified of the alleged thief.
GMP Chadderton tweeted: "We have received reports of a male stealing ducklings and goslings from the Salmon Field fishing lake in Royton and selling them on Facebook and Gumtree.
"An investigation is under way.
"The RSPB have been notified. Neighbourhood officers will be stepping up patrols in the area."
