Silver-backed needletail 
(Yến đuôi cứng bụng trắng, Hirundapus cochinchinensis)

The silver-backed needletail (Hirundapus cochinchinensis) is a species of swift in the family Apodidae. 
The bird species is found in Southeast Asia, Sumatra, Java and Taiwan.

As the name apodiforme—meaning "footless" in Greek—suggests, the legs of hummingbirds, swifts and treeswifts (or 'crested' swifts) are rather small and offer limited functional uses.
The family name, Apodidae, is derived from the Greek ἄπους (ápous), meaning "footless", a reference to the small, weak legs of these most aerial of birds.

The genus name Hirundapus is constructed from the names of the swallow genus Hirundo and the swift genus Apus.
Hirundo is a Latin word meaning swallow.
The word apus is Latin and derived from the Ancient Greek α, a ("without") and πளுக்கான, pous ("foot"), meaning "footless". 
The English name needletail is from the spined or thorny tail ends.
cochinchinensis: Latin for southern Vietnam.