A property developer who was forced to relocate a group of kangaroos rather than cull them to make way for a new housing development in Perth’s south say just under half have died during the relocation process regardless.

The troop of about 200 Western Grey kangaroos were fenced in on land near Baldivis Road, and were due to be "humanely tranquillised and euthanased" in coming months before first stage construction by Spatial Property Group on the Paramount Estate was due to begin.

The fenced in kangaroos in Baldivis were planned to be euthanised. Credit:Baldivis MLA Reece Whitby/Facebook

The plan was originally developed in consultation between the Department of Biodiversity, Conservation and Attraction, Terrestrial Ecosystems expert Graham Thompson and the developer, and acknowledged relocation of large numbers of kangaroos could have "poor animal welfare outcomes".

In his previous work, Dr Thompson previously stated kangaroo location was an "imperfect science" and said the outcome may not always be best for the animals.