Astringency is also the dry, puckering mouthfeel caused by tannins found in many fruits such as blackthorn, bird cherry and persimmon fruits. The tannins denature the salivary proteins, causing a rough "sandpapery" sensation in the mouth. Astringency tastes unpleasant to many mammals (including humans), which tend to avoid eating astringent fruit; conversely, birds do not taste astringency and readily eat these fruit. It is thought that fruit astringency gives a selective advantage to some plant varieties because birds are better than mammals at long-distance seed dispersal, often flying a great distance before passing the seeds in their droppings.