A cryptic new species of flycatcher (Tyrannidae: Suiriri) from the cerrado region of Central South America

Auk, The, Jan 2001 by Zimmer, Kevin J, Whittaker, Andrew, Oren, David C

ABSTRACT.-A new species of tyrant flycatcher (Suiriri islerorum) is described from the cerrado region of Brazil and adjacent eastern Bolivia. The species previously had been confused with Suiriri suiriri affinis, with which it is syntopic at multiple sites. The new species was first identified by voice. Although cryptically similar to S. s. affin is in many respects, the new species is readily identified by all vocalizations, bill size, color pattern of the tail, and shape of the central rectrices. Most distinctive are the male-female duets, which are accompanied by dramatic wing-lifting displays not performed by any congeners. Reciprocal playback experiments of tape-recorded vocalizations demonstrated that the new species and S. s. affinis do not respond to one another's vocalizations. We provide information on the natural history of the new flycatcher, along with spectrograms of its various vocalizations. We also provide vocal analysis of all other named taxa in Suiriri, and discuss the various intrageneric relationships. In particular, S. s. affinis and S. s. bahiae, although distinct morphologically, are vocally and behaviorally similar, and respond to one another's vocalizations in playback experiments. Received 27 December 1999, accepted 5 September 2000.

THE GENUS SUIRIRI has been the focus of taxonomic debate for decades. Two species traditionally were recognized, a short-billed, whitebellied nominate form Suiriri suiriri; and a longer-billed, yellow-bellied form, S. affinis. The apparent intermediacy of a large series of Suiriri from northeastern Paraguay led Zimmer (1955) to suggest that the two taxa were conspecific. Meyer de Schauensee (1966) and Traylor (1979) followed Zimmer in recognizing only one species of Suiriri, whereas Short (1975) did not agree that Paraguayan birds showed signs of intergradation and continued to recognize two species. Traylor (1982) reexamined the Paraguayan material in the American Museum of Natural History (AMNH), and found it as described by Zimmer, concurring that S. suiriri and S. affinis should be treated as conspecific. More recent authors have remained divided: Sibley and Monroe (1990) recognized two species of Suiriri, whereas Ridgely and Tudor (1994) recognized only one. As currently treated, the genus also includes one additional taxon, S. s. bahiae, a yellow-bellied taxon from northeastern Brazil. Hellmayr (1927) treated bahiae as a subspecies of S. affinis, from which he found it to differ from typical forms by "uppertail coverts dark hair brown like the tail; rectrices without any yellowish at the base and without the pale brownish apical band."

Zimmer (1955) pointed out an additional complication: five AMNH specimens of S. affinis from Mato Grosso and Goias, Brazil, all of which were anomalous in having a short, broad-based bill and with the "pale terminal band on the rectrices unusually wide and distinct, exceeding any other specimen at hand whether from the same or other localities and whether suiriri, affinis, or bahiae." Zimmer fur- ther noted that "the significance of this combination of characters is completely puzzling, since there is no allied group toward which these features, singly or together, suggest a trend." In his reexamination of Suiriri, Traylor (1982) commented on the five aberrent AMNH specimens and an identical specimen from Maranhao, Brazil (from the Field Museum of Natural History, Chicago; hereafter FMNH). In addition to the short bill and broad, pale tips to the rectrices, the six specimens further could be distinguished from typical affinis by their distinctly broader central rectrices and a lack of any contrasting pale edging to those feathers (Traylor 1982). Traylor noted that "ordinarily the close correlation of two such discrete and unrelated characters as the short bill and the coloration and shape of the rectrices would be strong evidence that we have two sibling species. I think that eventually this will prove to be true, but the possibility that the short-billed birds may somehow be related to the intergradation between affinis and suiriri cannot be ig- nored at this time." He concluded by stating "most important, without field studies of the various taxa, it is useless to speculate."

During the course of several years of field work at various sites in Brazil, Zimmer and Whittaker found that there were two markedly different vocal types of yellow-bellied Suiriri, one of which was relatively widespread, occurring from Amapi to Bahia to Goias; and the other which we knew only from the Chapada dos Guimaraes region of Mato Grosso. The first type included birds that, by both distribution and morphological characters, clearly were as- signable to S. s. bahiae, as well as birds that appeared to be typical of S. s. affinis. The second type was distinctive not only for its vocalizations, but also for its dramatic wing-flapping displays that invariably accompanied all territorial duets by mated pairs (see below). Reciprocal playback experiments conducted at multiple sites revealed that the two vocal types did not respond to one anothers' vocalizations. In September 1998, we found the two vocal types occurring syntopically near Cuiaba, Mato Grosso, Brazil. Close comparison revealed that one vocal type was noticeably short-billed compared to the other and had a distinct buffy terminal fringe to the tail, and that the birds were always assortatively paired with their own vocal and morphological types.