Wikipedia (or Vikipedio) says so (https://eo.wikipedia.org/wiki/Birda_ekkrio_(onomatopeo)), but it can also be "kŭak, kŭak", because onomatopoeias don't need to obey the rules for general words.
To march (walk with regular steps: Mil., with music), Marŝi [int.]; Marŝigi; Marŝo (as military command), Marŝ[u][']!
The Long March (ref. post WWII Chinese history) la Longa Marŝado. (Marŝadi also means "to hike")
Toddle = Marŝeti
See also: Paŝi, Piediri, Promeni
So, per the several dictionaries I consulted for the above, all of them respected in the community, Marŝi means both "to walk" and "to march." Paŝi means "to step," Piediri means "to go on foot," (or Malmane per Cseh) and Promeni means "to stroll casually, or promenade."
Make certain that you write this all down in your notebooks, there may be a test later.
It's just like in Portuguese, then. The verb "marchar" means "to march", and it can refer to either marching in a military sense, or to simply walking, although the second usage is relatively unusual, with "andar" or "caminhar" being preferred (like "promeni" would be in Esperanto).