Principal English Translation: 

to make discordant sounds, to murmur (speaking of people or birds)

James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 219.

Orthographic Variants: 
hicaoaca, icaoaca, icauaca
Frances Karttunen: 

(I)HCAHUACA for people or birds to meke a lot of noise / gorjear, cantar, hablando de pájaros (S), el ruido y el murmullo que hace la gente en la plaza (C) [(2)Cf.75v,(1)Tp.130].
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 96.

Lockhart’s Nahuatl as Written: 

(i)hcahuaca, ni. Class 1: ōnihcahuacac. more often seen with impersonal -tla-. 219

Attestations from sources in English: 

hicaoaca = it twitters (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 10 -- The People, No. 14, Part 11, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 113.

icahuaca = to sing (of birds)
Daniel Garrison Brinton, Ancient Nahuatl Poetry: Containing the Nahuatl Text of XXVII Ancient Mexican Poems (1887), 155.