Four little black sheep on Wednesday left the countryside and began their new careers in the city: working as eco-friendly lawn mowers in a largely working-class district in northeastern Paris.

Between April and October, the new "park workers" will graze grounds the size of eight tennis-courts in three two-week-long sweeps in a move to promote biodiversity and make the grooming of the capital's green areas more sustainable -- replacing both chemicals and lawn mowers.

Out of work, they will be resting back at a farm on the outskirts of Paris, the Ferme de Paris.

"For a lawn mowed 24 times a year, there is no biodiversity. When you use animals, the droppings attract insects and the insects bring birds," said Eco Terra president Alain Divo whose company plans and organises eco-pasture projects in French urban areas.

Grazing next to a ring road and by the foot of a giant grey building housing the capital's archive centre in the 19th arrondissement, the sheep seem to have adjusted to their new environment quickly.

"The fact that they graze right away means that they're going to get used to this very quickly," Ferme de Paris sheep-keeper Marcel Collet said, noting the project that was ordered by local authorities is a "first" for the city.

Collet said eco-pasture has existed in France for about 10 years, but "really began to develop in the past three years".

He said most of the animals used in the projects are local breeds that have been made redundant due to a more intense and competitive farming culture, where they have been replaced by more productive animals.

"Breeds that were a bit local, a little less productive... were set aside," Collet said.