Task: Question Answering
Input (English): Passage: Marojejy National Park is a national park in the Sava Region of northeastern Madagascar. It covers 55,500 ha (214 sq mi) and is centered on the Marojejy Massif, a mountain chain that rises to an elevation of 2,132 m (6,995 ft).  Access to the area around the massif was restricted to research scientists when the site was set aside as a strict nature reserve in 1952.  In 1998, it was opened to the public when it was converted into a national park.  It became part of the World Heritage Site known as the Rainforests of the Atsinanana in 2007.  Despite its rugged terrain, poaching and selective logging are still persistent problems, particularly since the start of the 2009 political crisis in Madagascar.  Mining, slash-and-burn agriculture, and wood collection also pose threats to the park and its wildlife.
The wide range of elevations and rugged topography of the massif create diverse habitats that transition quickly with changes in altitude.  Warm, dense rainforest can be found at lower elevations, followed by shorter forests at higher elevations, followed still by cloud forest, and topped near the peaks with the only remaining undisturbed mountain scrub in Madagascar.  Better growing conditions for plants can be found on the eastern side of the mountains, which receives more rain than the western side.  This habitat diversity lends itself to high levels of biodiversity.  At least 118 species of bird, 148 species of reptile and amphibian, and 11 species of lemur are known to occur within Marojejy National Park.  One of the lemurs, the silky sifaka (Propithecus candidus) is listed among "The World's 25 Most Endangered Primates".  The helmet vanga (Euryceros prevostii) is considered the iconic bird species of the park.
One path leads from the entrance of the park to the summit.  There are three camps along the route: Camp Mantella at 450 m (1,480 ft) in elevation in lowland rainforest, Camp Marojejia at 775 m (2,543 ft) at the transition between lowland and montane rain forest, and Camp Simpona at 1,250 m (4,100 ft) in the middle of the montane rainforest.  Camp Simpona acts as a base camp for the trek to the summit, a route that stretches 2 km (1.2 mi) and can take up to four or five hours to traverse. 
Question: What is the name of the animal species at the park that is among the top 25 endangered primates?
Output (English): silky sifaka.