520 ILCS 5/1.3

The seasons during which wildlife may be taken, the methods for taking wildlife, the daily bag limits, and the possession limits shall be established by the Department through administrative rule, but the Department may not provide for a longer season, a larger daily bag limit, or a larger possession limit than is provided in this Code. The Department is authorized to establish seasons for the taking of migratory birds within the dates established annually by Proclamation of the Secretary, United States Department of the Interior, known as the "Rules and Regulations for Migratory Bird Hunting" (50 CFR 20 et seq.). When the biological balance of any species is affected, the Director may, by administrative rule, lengthen, shorten or close the season during which waterfowl may be taken within the federal limitations prescribed. If the Department does not adopt an administrative rule establishing a season, then the season shall be as set forth in the current "Rules and Regulations for Migratory Bird Hunting". The Department shall advise the public by reasonable means of the dates of the various seasons. The Department may utilize the services of the staff of the Illinois Natural History Survey of the University of Illinois for making investigations as to the population status of the various species of wildlife. Employees or agents of any state, federal, or municipal government or body when engaged in investigational work and law enforcement, may with prior approval of the Director, be exempted from the provisions of this Act.