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The apparent diversification of Galapagos mockingbirds (Nesomimus) among the Galapagos Islands inspired Darwin’s initial conception of adaptive radiation (in which diverse forms arise through many generations from a single ancestor via local adaptation). Arbogast et al. (2006) used mitochondrial DNA (mtDNA) sequences to infer phylogenetic relationships among the various mockingbirds occurring across the Galapagos Archipelago. Their results indicated that the Galapagos mockingbird species and their inferred ancestor form a monophyletic group (i.e., a natural group consisting of an ancestor and all its descendants), suggesting a single colonization of the archipelago followed by diversification. Their analyses also indicated that Nesomimus is nested within the traditional mockingbird genus Mimus. Based on this result, use of the genus name Nesomimus is falling out of favor, with all the Galapagos mockingbirds being included in the genus Mimus (e.g., Arbogast et al. 2006; Lovette and Rubenstein 2007).
The southeast quadrant of the Galapagos Archipelago contains three species, each endemic to a single large island: the San Cristobal Mockingbird (N. melanotis) on San Cristobal; the Espanola Mockingbird (N. macdonaldi) on Espanola; and the Floreana Mockingbird (N. trifasciatus), which is now restricted to two islets adjacent to Floreana (efforts to recover this endangered species through appropriate tranlocations have received some guidance from analyses of the DNA of mockingbird specimens collected by Darwin on Floreana in 1835; see Hoeck et al. 2010). A fourth species, the Galapagos Mockingbird (N. parvulus), inhabits most other islands in the archipelago. Arbogast et al. found that most mockingbirds from the central and northern portion of the archipelago, which are currently considered conspecific populations of N. parvulus, do indeed appear to be closely related. However, based on their mtDNA analysis, Arbogast et al. found that N. parvulus on Genovesa (which are often recognized as N. parvulus bauri, e.g. Cody 2005) may actually be more closely related to N. melanotis and N. macdonaldi than they are to N. parvulus on other islands (the authors note that this possibility must be investigated further with multilocus data from the nuclear genome).
An intriguing study of the response of Marine Iguanas (Amblyrhynchus cristatus) to alarm calls of N. parvulus found that these lizards increase anti-predator vigilance behaviors when exposed to N. parvulus alarm calls. This is apparently the first known example of a non-vocal species associating the auditory alarm signals of another species with the threat of predation (in this case, the potential predator is often a Galapagos Hawk [Buteo galapagoensis]) (Vitousek et al. 2007).
Cody (2005) provides a detailed summary of the biology of this species.