We conducted playback-response experiments to assess whether the Brown-headed Nuthatch (Sitta pusilla) population found on Grand Bahama Island might be a distinct and critically endangered species. In one experiment, Brown-headed Nuthatch individuals in north Florida were presented with calls from: (1) a male conspecific in North Carolina; (2) a male recorded on Grand Bahama Island; (3) a male Pygmy Nuthatch (S. pygmae), a western congener; and (4) a male House Wren (Troglodytes aedon), which occurs in a different avian family (Troglodytidae). Vocalizations were broadcast at 20 locations, and detection and the proximity with which individuals approached the speaker were quantified. Nuthatches were detected at 0.72 (± 0.02; mean ± standard deviation) of trials where conspecific vocalizations were used, but were only detected half as frequently 0.27-0.30 (± 0.04) when Bahama Nuthatch and Pygmy Nuthatch vocalizations were used. Detections were least likely when House Wren vocalizations were used (0.15 ± 0.11). Nuthatches also approached the playback device more closely when North Carolina vocalizations were used. In a second playback assessment conducted in the Bahamas, males were three times more likely to respond when calls of a Bahama male were used versus calls of males in Florida. We also analyzed spectrograms of the two-syllable call notes produced by Bahama (N = 1) and continental (N = 10) males. The Bahama call has a higher peak frequency (6.1 vs. 4.8 kHz ± 0.6) and a slurred descent that extends over a broader frequency range (4.5 vs. 2.0 kHz). Results suggest that vocalizations of the Bahama population have diverged significantly and may affect interactions if the populations were to come into contact. Other genetic and morphological assessments also point to significant differences and support recognition of the Bahama Nuthatch as an independent species that may now be extinct. Variation des réponses aux vocalisations interspécifiques parmi les taxons parents des Sittidae : disparition imminente d'une espèce cryptique sur l'île de Grand Bahama ?RÉSUMÉ. Nous avons mené des expériences de réponses à des enregistrements de chant pour évaluer si la population de Sittelles à tête brune (Sitta pusilla) présente sur l'île de Grand Bahama pourrait être une espèce distincte et en voie de disparition critique. Comme première expérience, nous avons fait jouer les enregistrements suivants à des individus de Sittelle à tête brune du nord de la Floride :(1) un mâle conspécifique de Caroline du Nord; (2) un mâle enregistré sur l'île de Grand Bahama; (3) une Sittelle pygmée mâle (S. pygmae), un congénère occidental; et (4) un Troglodyte familier mâle (Troglodytes aedon), qui fait partie d'une famille aviaire différente (Troglodytidae). Les enregistrements ont été diffusés à 20 sites, et la détection et la proximité avec laquelle les individus se sont approchés du haut-parleur ont été quantifiées. Les sittelles ont été détectées dans une proportion de 0,72 (± 0,02; moyenne ± écart type) lors d'essais où des enregistrement...