The fauna of Venezuela consists of a huge variety of animals. Venezuela's diverse wildlife includes manatees, Amazon river dolphins, and Orinoco crocodiles, which have been reported to reach up to in length. Some 23% of reptilian and 50% of amphibian species that inhabit the country are endemic to Venezuela. Overall, around 8,000 species (the world's 5th highest total) are endemic to the country. Venezuela hosts a total of 1,417 bird species, more than 351 mammals, 341 reptiles, 315 amphibians and more than 2,000 freshwater and marine fishes. Invertebrates groups have not been inventoried exhaustively, but among the well known groups there are around 900 species of marine molluscs, 1,600 butterflies, over 120 dung beetles species and 39 species of blowflies. Birds There are 1,416 bird species in Venezuela, 45 of which are endemic. Forty-eight bird species that reside in Venezuela are considered threatened, and seven species have been introduced to the country. Important birds include ibises, ospreys, kingfishers, and the yellow-orange Venezuelan troupial, the national bird. Several expeditions to collect and document bird species in Venezuela took place in the 1930s and 1940s. These included one to Amazonas state by Ernest G. Holt for the Smithsonian, collecting over 3,000 specimens; a party led by William H. Phelps and his son, including Ernest Thomas Gilliard and Fèlix Cardona i Puig, which recorded over 2,000 specimens on Auyán-tepui; and a small collection amassed by F. D. Smith in Anzoátegui and Monagas. The Phelps family contributed significantly to the study of Venezuelan ornithology; an American explorer, William H. Phelps Sr. traveled extensively to the country, where his son was born and raised and where the William Phelps Ornithological Collection is kept. This collection grew from a series of expeditions to Venezuela's islands, tepuis, rural flatlands, great plains, and deserts. From the Phelps collection, at least 300 species have been identified, and the authoritative guides to birds of Venezuela have been developed. Habitat diversity Some birds resident in Venezuela span a variety of habitats; others are restricted to areas with certain types of vegetation. Birds which can live in any area of Venezuela, including its cities, include the bananaquit, black vulture, blue-gray tanager, great egret, and the tropical mockingbird, among others. Most birds of Venezuela span various habitats, but a few are specialized to only one area, typically due to extreme location or dependence on a certain resource; species restricted in this way include