Like many Christmas songs, "The 12 Days of Christmas" has become so familiar we rarely think about its weird lyrics, despite having plenty of chances every December.

Not only is the song is full of impractical presents — golden rings are cool; hopefully the leaping lords came with a gift receipt — but this true love also seems strangely obsessed with birds. Aside from the famous partridge, he or she gives the narrator more doves, hens, "calling birds," geese and swans than anyone really needs.

The song's 12-day theme is a religious reference, based on the biblical interval between Christ's birth and the arrival of the Magi (aka three kings or wise men). That has inspired lots of theories about the gifts' significance, including one suggesting they were originally a coded memory aid for oppressed English Catholics in the 16th century. But there's no evidence to support that idea, according to Snopes, which concludes the song probably began as a memory and counting game for kids.

Whatever its origins, "The 12 Days of Christmas" is now a staple of the Christmas canon. Carolers routinely rattle off its six avian gifts before moving to even larger quantities of maids, ladies, lords, pipers and drummers. But whether they're literal or symbolic, what kinds of birds are we singing about? And since these feathered offerings are singers themselves, maybe we should let them chime in?

Biologist Pamela Rasmussen thinks so, prompting the Michigan State researcher to compile a list of the most likely species for each bird mentioned in the song. Here are the six birds Rasmussen believes are forgotten stars from "The 12 Days of Christmas," including an audio recording of each one's unique song:

A partridge in a pear tree

Red-legged partridge (Alectoris rufa)

red-legged partridgeA red-legged partridge surveys the Midlands of England in winter. (Photo: Erni/Shutterstock)

The "partridge in a pear tree" is probably the red-legged partridge, Rasmussen says, a rotund seed-eater native to continental Europe. It was introduced to England as a game bird in the 1770s, and it's still common in the U.K. today. Another candidate might be the grey partridge, a wide-ranging Eurasian relative formerly abundant in Britain but now endangered there by habitat loss.

In either case, these are ground birds, laying eggs in terrestrial nests. They almost never perch in trees, the Royal Society for the Protection of Birds (RSPB) points out — even pear trees. Here's a 1960s recording of both, courtesy of the British Library:

Two turtle doves

European turtle dove (Streptopelia turtur)

European turtle doveA migratory European turtle dove perches on a branch in Bulgaria. (Photo: Erni/Shutterstock)

Next up are two European turtle doves, native birds that were widespread in the U.K. when "The 12 Days of Christmas" was introduced. They're migratory, breeding across much of Eurasia and North Africa, then wintering mainly in Africa's Sahel region. Their numbers and range have plummeted in recent decades, due to a mix of habitat loss and intensive hunting in some places during migration. The species was recently uplisted to Vulnerable on the IUCN Red List of Threatened Species.

The birds' common name comes from a "turr-turr" sound they make, not any relation to turtles. Here's a recording of a male singing to attract females in Loiret, France:

Three French hens

Red junglefowl (Gallus gallus)

Red junglefowlRed junglefowl, like this female in Thailand, are the ancestors of modern domestic chickens. (Photo: Jason Thompson/Flickr)

The three French hens are three female chickens, and Rasmussen suspects they're chickens from France, not a distinct breed. (In fact, while the song was popularized by an 18th-century English book, it may be based on an older French song.)

Domesticated chickens are descendants of red junglefowl, a wild member of the pheasant family that originated in South Asia. This species is now the most abundant bird on Earth, Rasmussen notes, although most live in captivity. Wild populations still exist in a variety of habitats from India to Indonesia, and chickens have also reverted to a semi-wild, ancestral lifestyle in some places, like Bermuda and Hawaii.

Here's a wild red junglefowl recorded at Pha Daeng National Park in Thailand:

Four calling birds

Eurasian blackbird (Turdus merula)

common blackbird"Calling birds" may refer to common blackbirds, also known as Eurasian blackbirds. (Photo: Rob Kemp/Shutterstock)

This one's trickier. There isn't a species named "calling bird," but there is a clue in the song's earliest-known print version, which appeared in the 1780 children's book "Mirth Without Mischief." There, the line reads "four colly birds," using an old English word for black. That suggests "calling birds" were originally blackbirds, and Rasmussen pegs the Eurasian blackbird (aka common blackbird) as a likely suspect.

Here's a recording of a Eurasian blackbird singing at midnight in Sweden:

Six geese a-laying

Greylag goose (Anser anser)

greylag gooseA greylag goose trudges through snow in central England. (Photo: Erni/Shutterstock)

The six nesting waterfowl are greylag geese, Rasmussen says. These are the ancestors of most domestic goose breeds, and according to the RSPB, they're also the "largest and bulkiest" of any wild geese native to the U.K. and Europe.

Greylag geese are a common sight at ponds and marshes across Eurasia, where they migrate between northern breeding grounds and more southerly winter retreats. They're known for a distinctive hoarse honk, captured in the recording below:

Seven swans a-swimming

Mute swan (Cygnus olor)

mute swanOne mute swam goes a-swimming at Forfar Loch in Angus, Scotland. (Photo: Mark Caunt/Shutterstock)

Finally, the seven swimming waterfowl are most likely mute swans. These large birds were long kept in semi-domesticity in England, where they were considered property of the Crown. Although some were eaten at banquets, royal protection may have saved them from being wiped out by hunting, as they were in other places.

Mute swans were introduced to North America in the 19th century, where they're now deemed an invasive species. They do make less noise than other swans, but they're not exactly mute. Here's one recorded in Devon, England, in 1966:

And, as a holiday bonus, here's a recording of a mute swan taking off from water. As Rasmussen explains, the swans' loud wing beats help them advertise and defend their territory, filling a role normally played by song in more vocal birds:

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.