A multi-character systematic study led by the Universidade Federal do Pará shows that what ornithologists know as the silvery-cheeked antshrike (Sakesphoroides cristatus) actually represent two species rather than one.
Illustration of Sakesphoroides niedeguidonae. Image credit: Eduardo Brettas.
The newly-discovered species, the northern silvery-cheeked antshrike (Sakesphoroides niedeguidonae), is endemic to the Caatinga, a natural region that lies in the hinterland of northeastern Brazil.
“The Caatinga is the largest patch of seasonal dry tropical forest in the Neotropics, located in northeastern Brazil and characterized mainly by deciduous vegetation and extreme rainfall seasonality,” said Dr. Pablo Cerqueira from the Museu Paraense Emílio Goeldi at the Universidade Federal do Pará and his colleagues.
“It has historically been treated as a biologically impoverished domain, but recent studies uncovered new diversification patterns and several new species of frogs, mammals, insects, and fishes.”
“The geomorphology of this region plays an important role in its biogeographic history, with altitudes ranging from sea level in the north, an average 400-700 m through Bahia and Minas Gerais states in the central part, to over 1,000 m on the slopes of the Espinhaço range.”
Sakesphoroides niedeguidonae is only the second species known in the genus Sakesphoroides, which also includes Sakesphoroides cristatus.
“Until recently, Sakesphoroides cristatus was placed in the genus Sakesphorus, but novel genetic and morphological data recovered it as non-monophyletic, prompting the transfer to the separate genus Sakesphoroides,” the researchers said.
In the study, they examined a total of 1,079 Sakesphoroides cristatus specimens (818 males, 261 females).
To investigate song variation, they analyzed a total of 115 different sound recordings.
They also sequenced 58 tissue samples from throughout Sakesphoroides cristatus range, 39 of them belonging to the left bank and 19 to the right bank of the São Francisco River.
Of the 1,079 individuals (skins and photographs) analyzed, they could not identify any diagnostic plumage differences among males, but two main plumage patterns in females were diagnosed mostly across the river.
“Males of Sakesphoroides niedeguidonae are similar in plumage to Sakesphoroides cristatus, but females differ from the former by distinct crown, back, and tail colors,” the scientists said.
“Sakesphoroides niedeguidonae has an overall lighter (amber) color rather than chestnut as Sakesphoroides cristatus.”
“The back is olive brown in Sakesphoroides niedeguidonae, whereas that of Sakesphoroides cristatus is cinnamon-brown.”
“The overall tail color in Sakesphoroides niedeguidonae is darker than in Sakesphoroides cristatus, with the most conspicuous difference being the black and white barring, replaced in Sakesphoroides cristatus only by discreet dull brown and rufous bars and complete absence of white barring.”
“The loudsong of Sakesphoroides niedeguidonae is slightly similar in general pattern to that of Sakesphoroides cristatus, but differs conspicuously by the shape of the first notes,” they added.
“The new species is almost restricted to the left/northern bank of the São Francisco River, with one population occurring on the right bank at ‘Raso da Catarina’ region in Bahia state.”
“This population found on the right/southern bank of the São Francisco River could have been ‘transferred’ across the river due to paleocourse shifts, as discussed in detail below in discussion section.”
Sakesphoroides niedeguidonae is a common species in most of its distribution, occurring in different habitats in the Caatinga, including secondary growth vegetations.
“The extent of occurrence is estimated at 630,000 km2, not approaching the threshold for a Vulnerable status under the IUCN range size criterion (less than 20,000 km2),” the authors said.
“Although no data on population size are available, we expect a number greater than 10,000 mature individuals, so this species is best placed as Least Concern.”
“However, new approaches using niche modeling for future climate scenarios support a significant reduction in range size of Sakesphoroides cristatus (including Sakesphoroides niedeguidonae, as treated before this study).”
“Applying IUCN criteria to these future estimated range sizes can change its threat category to Near Threatened and even Vulnerable depending of the future global change scenario.”
The discovery of Sakesphoroides niedeguidonae is reported in a paper in the journal Zoologica Scripta.
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Pablo Cerqueira et al. A new antshrike (Aves: Thamnophilidae) endemic to the Caatinga and the role of climate oscillations and drainage shift in shaping cryptic diversity of Neotropical seasonal dry forests. Zoologica Scripta, published online June 17, 2024; doi: 10.1111/zsc.12672
