“Bright-eyed and busy-tailed” means cheerful and lively, alert and eager, with lots of energy.
The Oxford English Dictionary says the phrase originated in America.
From the Encyclopedia of Word and Phrase Origins by Robert Hendrickson: “Bright-eyed is obvious and the bushy-tailed here is a reference to the tail of a cat, which fluffs up when the animal becomes excited. It dates back to the 19th century.”
The two terms developed independently of each other. “Bright-eyed” supposedly comes from the late 1500s, while “bushy-tailed” is said to have originated around 1865-1870, though no direct source is clear for either.
They were seen together for the first time in talking about a squirrel. Anybody who has watched squirrels will agree that it’s an apt description. Squirrels are alert, most with big, fluffy tails, and they’re very fast on their feet.
In St. Clair County, Michigan, Its History and Its People, published in 1912 by William Lee Jenks, we can read about the impossible attempt to capture the following in a painting: “…to see the wild pigeon, chewink, fox sparrow, bobolink, scarlet tanager, the bright-eyed and bushy-tailed squirrel, the graceful motions of water birds…”
The phrase is usually used to describe a person who bounces out of bed in the morning prepared to conquer the world. For example, the 1968 novel The Technicolor Time Machine by Harry Harrison contains the sentence: “You look very bright-eyed and bushy-tailed this morning.”
I’ve also read the squirrel described as “a rodent with a great personality.” Of course, some people can be described that way, too.