Using Partizip II would be correct if zu is omitted:
Das Töten von Tauben ist allerdings eine nicht gestattete Maßnahme.
The Partizip II cannot be used with zu in this kind of sentence. This combination with zu only works with the infinitive and the Partizip I. This combination is used predicatively with the infinitive and attributively with Partizip I. The combination of zu and Partizip I is sometimes called gerundive (Gerundivum in German), following languages like Latin where a distinct verbal form with this name exists.
Despite Partizip I having active meaning if used on its own, the combination with zu has passive meaning. It expresses necessity or - in the case of negation - impossibility. Becauseof this, Das Töten von Tauben ist allerdings eine nicht zu gestattende Maßnahme is correct.