You need black cardboard, or construction paper, with the eyes of various animals cut out of reflective tape, glued on to the cardboard. The eyes need to be of the correct shape and size for the specific animal, and you need to mark on the cardboard the approximate height off the ground that the animal's eyes would be. (I would maptack, or laminate my cards, for reuse!) Each participant in the game is given a photocopied sheet with details about the various animals that she will spot, a picture of the eyes, and the height off the ground that they will be found.
Each girl will need a flashlight! Or at least each group of girls will need a couple.
The eyes need to be hung, or placed in the grass, or bushes, at the appropriate height before the stalking game begins so that the participants don't see you setting them up. Try to set things up so that the cardboard will not move in the wind and twirl around so that the reflective part of the cardboard is not facing the trail.
Guides and Up.
I would divide the girls into groups of 5 or 6. You need to do this when it is quite dark, otherwise the eyes do not reflect back.
The girls are to go out in groups and find the 10 or 12 eyes that are on their list. The eyes should be along a trail, so that they can be found fairly easily and so that the girls do not get lost. The end of the trail, or turning point if it is not a loop, should be well marked.