Rhamphotheca Removal By A Potassium Thioglycolate Based Solution - A Complementary Technique For Complete Cleaning Of Delicate Passerine Skulls

The horny sheath known as rhamphotheca covers at least partially four bones of upper maxilla and two from mandible, precluding the observation of their structures and hindering proper osteological studies of the beak. The two main methods currently used for skeleton preparation, viz. the use of dermestid beetles and maceration, can effectively remove the rhamphotheca, however, with possible drawbacks to the material and lasting long to clean it entirely. We developed a new method to remove the rhamphotheca by using a potassium thioglycolate plus calcium hydroxide plus urea based solution (commercially available as chemical depilatory creams), which breaks sulfide bridges of keratin thus softening this structure. Results of our tests with 69 passerine skulls suggest the more efficient proceeding is to apply the cream on bill with intervals of one to two hours, repeating these applications during four to seven hours and then rinsing the material. The remains of rhamphotheca and subjacent dermis can be removed easily with tweezers while the material is still wet. This new method does not damage the material and can be applied in skulls already deposited in osteological collections, besides being faster than the other methods, allowing the removal of the rhamphotheca in less than one day.