As is the case with many neotropical birds, many aspects of the basic biology of the White-crested Elaenia are poorly-known. The wintering distribution is poorly-documented; this should be unusual for such a common and widespread species, but in the case of this species, perhaps considerable fault lies with the difficulties of identifying White-crested Elaenia in the field, especially when it is not breeding. Nonetheless, we do not know whether the bulk of the population winters in the Andes or in the lowlands of central or eastern South America; or to what extent it winters in the Amazon Basin. Although White-crested Elaenia breeds in many places in the Andes from Colombia south to northwestern Argentina, there are large areas in eastern Peru from which there are no known breeding populations of this species; are these gaps real?
Hybridization has been suspected between White-crested Elaenia and the Sierran Elaenia in Colombia and Ecuador; are these taxa hybridizing, or is our understanding of the molts and plumages of Elaenia so incomplete that we do not have accurate criteria with which to distinguish these two seemingly very different species?
Most aspects of the breeding biology of White-crested Elaenia remain unknown: territory size, population density, incubation and nestling periods, diet, etc. Similarly, how migrant chilensis White-crested Elaenia interact on the wintering grounds with resident elaenias, including other populations of White-crested Elaenia, remains unknown.