Birds belonging to two owners, who live next door to one another on Severn Drive in Garforth, were killed in a spate of incidents over the course of a week.
Animal lover Craig Jenkinson, who has kept Campbell ducks for several years, has seen four of his animals decapitated by a “sadistic” killer.
He said: “I’m disgusted that anybody could be cruel to animals in this way. We’ve always had animals because we wanted to instil in our children the idea of looking after other living things.
“You have to ask, where does it go from here? If they’re capable of doing this, the next step could be that they’re attacking a dog, or even a child.”
Mortgage specialist Mr Jenkinson, 44, has a number of pets at his home, which backs onto open land. He dismissed the first incident, which happened on March 2 and left one duck dead, as a fox attack.
But after three others were killed in further attacks he said he became suspicious.
“It’s too coincidental,” he said. “If it was a fox it would have slaughtered all six, not one at a time. I know people are cruel to animals, but when it’s your own it’s heartbreaking.”
Police said the fact that the ducks were kept in a pen and that they were beheaded with “clean straight cuts” suggests they were the victims of a human killer.
Officers are linking the attacks to another incident, overnight on March 9, in which two ducks belonging to Mr Jenkinson’s neighbour were shot dead.
PC Andy Gaitley, of the Leeds Outer East Neighbourhood Policing Team, said: “Both owners are understandably extremely upset at these attacks on their pets.
“We would urge anyone with information or who has heard rumours about who may be responsible to contact the Leeds outer east neighbourhood policing team.”
Anyone with information should call police on 101.