I received -- as a gift -- a small skull mounted on a carved wooden background, typical of Bavaria. I've looked online but am confused about US customs requirements. Can I bring this through? If not, and I declare it, will they just confiscate the item or will I just be fined?
You really shouldn't have a problem. From the CBP site:
Bones, horns and hoofs that are imported as trophies may be imported without further restrictions if they are clean, dry and free of undried pieces of hide, flesh, or sinew.
For further concerns CBP refers you to APHIS for further information as this is an actual regulatory body responsible for import of animal byproducts:
Many animals, game birds, products and byproducts from such animals and game birds are prohibited, or allowed only restricted, entry into the United States. Specific requirements vary according to the country of export. For more information about importations by country, please call the USDA, Animal and Plant Health Inspection Service(APHIS), the National Import-Export Center, tel. (301)851-3300, fax (301)734-8226. Since hours of service and availability of officers from the other agencies involved may vary from port to port, you are strongly urged to check with your anticipated port of arrival before importing a pet or other animal. This will assure expeditious processing and reduce the possibility of unnecessary delays.
However if you are concerned about it still you can ship it to yourself and avoid bringing it over the border on your own.
Hopefully you were able to bring your deer skull home safely but if anyone else was wondering...here is a comprehensive list of sports equipment that you can and can't bring on airlines based in America.
(Technically a deer skull would be sports equipment b/c it is a product of hunting.)
Tld;r: While a part of it is based on international regulations, most likely it depends more on the airline and its policies.