Using pentosidine levels in bird skin to determine how old they are is a relatively new method of aging. Up until now, previous studies have focused on analyzing skin from the breast. Current research is being done on analyzing patagium skin samples so that wild birds can be sampled without causing much harm to them. Fallon et al. (2006) suggested that the level of pentosidine is different in various locations of a bird's body. Forty milligram skin samples from the breast and patagium of 25 monk parakeets (Myiopsitta monachus) and 25 double-crested cormorants (Phalacrocorax auritus) were analyzed. There was a significant difference in the level of pentosidine when comparing breast and patagium skin. This suggests that it is important to consistently obtain samples from the same part of a bird's body when working on an aging project.