The problem with animal skins is that they actually need to be kept in relatively humid conditions otherwise they split quite easily. I can get the proper Relative Humidity figures for natural science collections at work tomorrow. (I work in a museum) In other words though don't place your capes and skins near a radiator or anywhere that can be too drying. This should help prevent splits in capes and skins. Oiling the back of the skins is a way of keeping moisture in. However, oils are also a food source for pests which tend to find fur and feathers totally yummy. So Keep checking your boxes. If you do feind moths, carpet beetles or other such pests, you should freeze your collection. Put in a selaed bag and put in the freezer for three days which should kill off any larvae.
If you are feeling really anal you can keep your feathers in air tight containers and use products such as absorb and silica gel to control the environment of your capes and feathers.
This is quite a good guide to preventative conservation of feathers.
http://www.bishopmuseum.org/research...v-feathers.pdf