Is the northern hawk owl endangered?

The term "hawk" is not a scientific or taxonomic designation of a single bird, but is more of a common Word used to refer to many different birds, perhaps as many as 200 different species. The true hawks alone comprise 48 species.

It would be best if you would rephrase the question to refer to a specific species or a type of "hawk" indigenous to a particular area.

In any case, one member of the broader "hawk" family that did face extinction 30 to 40 years ago is the peregrine falcon. The widespread use of the pesticide, dichlorodiphenyltrichloroethane (DDT) in the 70's, caused this birds eggs to be thin-shelled and unable to support life. DDT was permanently banned from use.

Fortunately, a number of falcons had been captured for breeding, most notably at the University of Guelph in southern Ontario, and today this beautiful and majestic bird thrives, not only in Ontario but in many US states and also in Mexico.

We make mistakes, but we can correct them too if we act quickly enough.