I think that in this case “clouc” just attempts to reproduce the sound that a poule makes – I know those animal sounds are entirely different in Japanese I am not sure whether it is a dialect or not, I think it is just an onomatopoeia, like “tic tac” for a clock … Another, more standard onomatopoeia in French would be “Cot-cot, Cot-cot-codêêêc”.

In English, we say that hens cluck. It is a clucking sound.

The site below shows this means cluck.

“vu la saison il y a de fortes chances pour qu’elle couve, , si quand on le touche elle glousse de mécontentement, et gonfle les plumes, que quand elle sort elle fait “clouc clouc”, c’est qu’elle couve.”

http://www.poulesoieclub.com/t5887-faire-decouver-une-poule

La poule fait clouc.
The hen clucks or is clucking.

Clouc clouc is not known as is in French but is likely from Occitan and not Basque.

In Occitan, cloc pronounced kluk = clouc is the name of the sound made by a cloca, a broody hen. This sound is transcribed as cot cot cot codet/codec in French.

Its root can also be found in Spanish where cloquear and gallina clueca are both related to a broody hen. In French, the equivalent would be cocotte.

While clouc is undoubtedly an onomatopoeia like its English counterparts “cluck” and “cackle”. Clouc might also be given a Latin root: the verb glocare which gave the French glousser.

Wikipedia suggests an indo-European root, *klag, so that might be a very ancient onomatopoeia.

References: cloc cloca clueca cloquear glocare clangare