In The Pioneers, birds represent the abundance of the untamed American wilderness. They are natural resources, seen as part of God's creation, and should be used carefully. Natty Bumpo does kill birds for food and shows what a good shot he is in his ability to hit a wild bird, be it pheasant or a turkey.
Natty, however, is alarmed when Dick Jones, in the chapter "The Slaughter of the Pigeons," uses a cannon to kill a mass of pigeons for food. To Natty, this kind of severe overkill violates the proper relationship between humans and the natural world. As Natty says to Judge Marmaduke:
It is much better to kill only such you want, without wasting your powder and lead, than to be firing into God’s creatures in such a wicked manner.
Taking more than you need is described not only as waste but as wickedness or moral evil. The novel explores the struggle between the forces of civilization pouring into Natty's beloved wilderness and the need to preserve what is best in the natural world.