Northern Prairie Wildlife Research Center
Bark or wood chips may be used as nest material and will last for several years if the chips are large enough (2 to 3 inches) to resist being blown out by the wind. A combination of large decorative bark and smaller chips or straw also works well and in some cases is preferred by geese. Sawdust should not be used because it traps moisture and is easily blown out. Expanded shale landscaping rock (3/8-inch diameter) mixed with chips or straw has been used successfully and is fairly long lived. Expanded shale is different from cinders or lava rock; it resembles pea gravel but weighs half as much.
Because nest materials will blow out or deteriorate and structures may break or tip, post, tree, and floating nest structures must be inspected and refilled by March 1 each year