Avian Conservation and Ecology (Dec 2020)
Variation in responses to interspecific vocalizations among sister taxa of the Sittidae: imminent extinction of a cryptic species on Grand Bahama Island?
Abstract
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.
