DOC staff discovered the dead hawk had tethers attached to its legs.
"It is never okay to treat a wild bird badly in order to domesticate it," DOC East Coast operations manager John Lucas said.
"The bird was extremely underweight and in poor condition."
Lucas said it appeared the hawk may have escaped attempts to be trained but was left unable to feed "resulting in its death".
He said the graceful harrier hawks were a valuable part of the country's landscape and deserved to be well treated.
"We all have a responsibility to care for Aotearoa and our special native species.
"Human behaviour has a big impact on wildlife and DOC has been actively out and about this summer educating and encouraging people on the Kiwi way to better protect our landscapes and native animals."
Harrier hawks are partially protected under the Wildlife Act 1953 and possession of them is strictly regulated.
DOC staff could only speculate as to how it came to be in the hands of the person who had attached what turned out to be fatal tethers.
It may have been grabbed while a young chick or may have been caught in a net trap.
It was not known at this stage how old it was and it has been sent to Wildbase Hospital at Massey University for a necropsy and further analysis.
Anyone with any information about the incident is asked to contact 0800 DOC HOT (0800 362 468).