It was a generalist predator, taking prey of the same size as small eagle species do: land animals weighing one or a few kilograms.

However, essentially identical bones had been found about 100 years earlier by Augustus Hamilton and discussed subsequently by Henry Ogg Forbes; this material probably comes from the Te Aute region in the North Island.

C. teauteensis is considered valid, based on the argument that as with many New Zealand birds, it is reasonable to assume that North and South Island populations were at least distinct subspecies, if not species.

But even though Kálmán Lambrecht mentioned a putative holotype tibiotarsus (which still exists in the BMNH) he explicitly stated that Forbes' names were both invalid.

In addition, harrier bones of comparatively recent age in the collection of Walter Mantell, assigned to C. gouldi (an obsolete name of C. approximans) by Richard Lydekker, seem to be of a more robust bird judging from the published descriptions; this material may now be lost, but all things considered it is not unlikely to be the first remains of Eyles' harrier known to science.