The fauna of Puerto Rico is similar to other island archipelago faunas, exhibiting high levels of endemism and low, skewed taxonomic diversity. Bats are the only extant native terrestrial mammals in Puerto Rico. Other terrestrial mammals are introduced species such as cats, goats, sheep, the Indian Mongoose, and escaped monkeys. Marine mammals include dolphins, manatees and whales. Of the 349 bird species, about 120 breed in the archipelago and 47.5% are accidental or rare. The most recognizable and famous animal of Puerto Rico is probably the coquí, a small endemic frog and one of the 85 species that comprise Puerto Rico's herpetofauna. No native freshwater fish occur in Puerto Rico, but some species, introduced by humans, have established populations in reservoirs and rivers. The low richness-high diversity pattern is also apparent among invertebrates, which constitute most of the archipelago's fauna. The arrival of indigenous people about 4,000 years ago and, to a larger extent, of Europeans more than 500 years ago had a significant impact on Puerto Rico's fauna. Hunting, habitat destruction, and the introduction of non-native species led to extinctions and extirpations. Conservation efforts, the most notable for the Puerto Rican Parrot, began in the second half of the 20th century.