During episodes of courtship, Bermuda Petrels vocalize frequently, typically in pairs, although "practicing" groups of petrels, presumably subadults and unpaired adults, can be seen flying together and vocalizing, usually 3-5 birds. As is the case for similar species of gadfly petrels that are nocturnal on the nesting grounds, most vocalizing occurs in the late afternoon and through the night, and calling is more often heard during windy periods and on nights with little or no visible moon. The male initiates bouts of calling, flying ahead of the female and producing a tremolo, high oooooooooooooo-EEK! The female responds antiphonally with a lower-pitched, more gravelly, growling or moaning aaaaaaaawww-AK! (Spanish seafarers in the sixteenth century associated these sounds with spirits or devils.) Adults returning to the nest site, but not courting, make short, high-pitched, modulated contact calls that Murphy and Murphy (1951) describe as "single, soft screepy notes" and that Shepard (1952) describes as "loud, scratchy eet noises." On the nest, petrels frequently make shorter calls, similar in quality to the male's tremolo, that sound remarkably like a whining puppy; they also make lower-pitched calls, similar to the female's courtship call, but shorter.
Chicks and fledglings make a variety of peeping, squealing, and squeaking vocalizations when interacting with adults or being handled by humans. Jeremy Madeiros (in litt.) describes the typical chick call as cheep-cheep-cheep-cheep for at least the first 7-8 weeks (45 to 60 days, corresponding to approximately half to two-thirds fledged). After about 60 days, chicks often start to vocalize more like the adults, with calls a bit higher in pitch, with what local researchers call the "puppy" or "ecstatic" call (a rapidly repeated ooo-eek, ooo-eek, ooo-eek). As adult birds arrive to feed an older chick (half-fledged or more), the chick may be very aggressive in demanding food, emitting a low-pitched "growling" sound awrrrrrrrrrr. After being fed, chicks will then settle back into a quiet, satisfied, repeated cheep every 5-10 seconds, a series that may go on for 30 minutes or longer. The fledglings in the last week or two before fledging, and especially during the pre-departure exercising stage, begin to vocalize like the adults, especially if they come across other Bermuda Petrels while out of their burrows exercising, delivering full-throated ooooooooo-eek or aaaaaaaaah-eek calls, ecstatic calls, or "moaning" calls.
Bermuda Petrel's local name, "Cahow," is called by Beebe (1935) "a very feeble onomatopoeic attempt, the voice of these birds possessing a wild, haunting quality quite impossible to express in human syllables." (It should be noted that Beebe had received one Bermuda Petrel corpse from a lighthouse keeper and had never heard the species vocalize; nevertheless the description and enthusiasm are hardly inapt.) Shepard (1952) writes that their "calls were in strange harmony with the crashing of the waves against the base of the tiny islet and the continuous whine of the strong, stormy-season winds."
The sound of the word "cahow" (often rendered "cahowe" or "cowhowe" in early writings about the species) more closely resembles the lower, throatier call of the female, given mostly during courtship flights and described by Wingate (1960) as "an eerie hollow wail".