a pod of

　スリランカの海で溺れかけの象2頭を救出しました。

Mammoth effort: Sri Lankan navy rescues two elephants washed out to sea

Two young elephants washed out to sea have been saved from drowning by the Sri Lankan navy in the second such incident off the island in as many weeks.
The navy said the pair of wild elephants were brought ashore on Sunday after a mammoth effort involving navy divers, ropes and a flotilla of boats to tow them back to shallow waters.
Photos showed the elephants in distress, barely keeping their trunks above water in the deep seas about half a mile off the coast of Sri Lanka.
（省略）
They are not the only wildlife to encounter trouble in the biodiverse island. In May, the navy and local residents saved a pod of 20 pilot whales that became stranded in Trincomalee, a natural harbour that is popular for whale-watching.

https://www.theguardian.com/world/2017/jul/23/sri-lanka-navy-rescues-two-elephants

　“a pod of”を取りあげます。クジラの「群れ」を指すようですが、他にも「群れ」を表す語はいくつかあるので違いを調べてみました。

　まず、“pod” /pάd｜pˈɔd/を『ジーニアス英和辞典』（第五版、大修館書店）で調べると「（クジラ・イルカなどの）群れ」とあり、“a pod of whale”で「クジラの群れ」という例文が記載されていました。LDOCEでは“a group of sea animals, such as whales or dolphins, that swim together”と定義されており、海の生き物の群れを指すようです。他にも似たような意味を持つ単語として“herd”を見てみると“group of animals of one kind that live and feed together”、さらに“flock”を調べると“a group of sheep, goats, or birds”とありました。動物ごとに単位が変わるように「群れ」でも使われる語は変わってくるようです。(flying bird)