The vocalizations of some populations of White-crested Elaenia are well-known, but apparently are not well known for some other subspecies, such as the intra-tropical migrant subspecies modesta.
The dawn song of the southern subspecies chilensis is a short, slightly raspy two- or three-note phrase, e.g., these examples from Chuquisaca, Bolivia (at the northern limit of the distribution of chilensis), and from Jujuy, Argentina. The call of chilensis, at least on the breeding grounds, is 'feeeo' or 'feeo-feeo' (the Chilean name for White-crested Elaenia is 'fío-fío'); this call may be repeated incessantly for long periods.
The dawn song of griseogularis has been transcribed (Lane, in Schulenberg et al. 2007) as a series of deep, burry, falling-rising 'djeewee ' notes interspersed with occasional 'per'brr'djwee' notes. Daytime calls of griseigularis are raspier than the call of chilensis. The call of modesta is a pure, descending 'peeur' (Lane, in Schulenberg et al. 2007).