Morton L. Isler

SPECIES LIMITS IN ANTBIRDS (THAMNOPHILIDAE): THE WARBLING ANTBIRD (HYPOCNEMIS CANTATOR) COMPLEX

Abstract Six populations of Warbling Antbird (Hypocnemis cantator) currently considered subspecies are more appropriately recognized as species, given the multiplicity of vocal differences that distinguishes them. These vocal differences are as great or greater than vocal differences documented between syntopic species-pairs in the family Thamnophilidae (Isler et al. 1998). Evidence is also provided that two forms currently considered subspecies are syntopic and that two others are parapatric without apparent physical barriers. Vocally, the pair of syntopic taxa were distinguished dramatically, but solely, by common calls. The finding that common calls were as diversified as songs in this species-group suggests that calls may be as important as songs in reproductive isolation. Future field studies should therefore focus on clarifying the function of different types of thamnophilid vocalizations and elucidating their role in speciation. This is the first contribution to a multifaceted analysis of the vocalizations and genetic structure of typical antbirds (Thamnophilidae) in Amazonia. In future work, results of the vocal analysis will be compared with a parallel genetic study, after which the two analyses will be integrated to suggest a phylogeny. The present study and preliminary studies of genetic differentiation (e.g., Bates et al. 1999) make it clear that the H. cantator complex has had a long evolutionary history that produced greater species-level diversity than was recognized previously. Límites de Especies en Thamnophilidae: El Complejo de Hypocnemis cantator

Species limits in antbirds (Passeriformes : Thamnophilidae) : The Myrmotherula surinamensis complex

Current species-level taxonomy of Neotropical birds is in need of reassessment but lacks objective methodology and criteria for the ranking of allopatric populations. Previously (Isler et al. 1998), through empirical analysis of pairs of syntopic species, we developed methods and standards for employing vocalizations in determining species limits in the family Thamnophilidae. Building on this study, we now propose procedures for integrating vocal characters with morphology and geographic distribution in making species determinations in thamnophilids. We applied this methodology to populations of antwrens in the Myrmotherula surinamensis complex (including three subspecies of M. surinamensis and M. cherriei). Four diagnostically differentiated populations were identified, all of which corresponded to named taxa. Each population (some of which are narrowly sympatric) was distinguished unambiguously by morphology and vocalizations. Under these objective and conservative standards, we recommend that Myrmotherula surinamensis, M. multostriata, M. pacifica, and M. cherriei be recognized as distinct species. The level of differentiation found between M. surinamensis and M. multostriata illustrates the minimum threshold recommended for species status of allopatric populations of thamnophilid antbirds and should provide a useful reference point for future considerations of species limits.

CLINAL VARIATION IN VOCALIZATIONS OF AN ANTBIRD (THAMNOPHILIDAE) AND IMPLICATIONS FOR DEFINING SPECIES LIMITS

Abstract In avian taxa in which vocalizations are considered innate, such as suboscine passerines, vocal characters are increasingly being used to help determine whether populations have achieved species status. In comparing vocal characteristics of distant populations, however, one must be concerned with the possibility of character gradation through intermediate populations. The first quantitative study of a species in a suboscine family to test for clinal vocal variation, our vocal study found clinal variation in the pace (number of notes per second) of male loudsongs, and revealed that the geographic pattern of the clines was consistent with genetic variation found in the companion molecular study (Brumfield 2005). The result underscores the necessity of searching for intermediacy when analyzing vocalizations of geographically distant populations. Furthermore, given that male loudsong pace was the only vocal character that varied across the intergrading populations, the result also provides support to the guideline that one should expect thamnophilid species to differ in at least three vocal characters (Isler et al. 1998) and indicates that this degree of vocal character differences can be a valuable “yard stick” in determining which thamnophilid populations have achieved biological species status.

A NEW SPECIES OF PERCNOSTOLA ANTBIRD (PASSERIFORMES: THAMNOPHILIDAE) FROM AMAZONIAN PERU, AND AN ANALYSIS OF SPECIES LIMITS WITHIN PERCNOSTOLA RUFIFRONS

Abstract Ornithological studies undertaken in certain sandy soil habitats of lowland northeastern Peru uncovered a previously undescribed species of Percnostola antbird. Elements of its morphology, vocalizations, and behavior indicate that it should be considered a well-differentiated species, closely related to P. rufifrons. We present a description of the new species; an analysis of how it differs from the four previously described subspecies of P. rufifrons; and a reconsideration of species limits within P. rufifrons, employing measures of morphology, vocalizations, and behavior. Under guidelines developed previously (Isler et al. 1998, 1999), vocal differences among the four subspecies (rufifrons, subcristata, minor, and jensoni) of P. rufifrons were insufficient to support considering them distinct species. However, differences in morphology among most of the four taxa were substantial, and we look forward to genetic studies of Percnostola and related groups. The localized and highly specialized habitat preferences of the new species cause grave concern for its conservation. RESUMEN.—Estudios ornitológicos realizados en hábitats de arena blanca de las tierras bajas del nororiente peruano permitieron el descubrimiento de una nueva especie del género Percnostola. Elementos de su morfología, vocalizaciones y comportamiento claramente diferencian esta especie, y sugieren una relación cercana a P. rufifrons. Presentamos una descripción de esta nueva especie; un análisis de cómo se diferencia esta especie de las cuatro subespecies previamente descritas de P. rufifrons; y una reconsideración de los límites específicos dentro de P. rufifrons, empleando medidas de la morfología, vocalizaciones y comportamiento. Siguiendo los lineamientos desarrollados en anteriores publicaciones (Isler et al. 1998, 1999), diferencias vocales entre las cuatro subespecies previamente descritas de P. rufifrons (rufifrons, subcristata, minor y jensoni) fueron insuficientes para considerarlas especies diferentes. Sin embargo, diferencias morfológicas entre la mayoria de estos cuatro taxones fueron substanciales, por lo que es necesario esperar futuros estudios genéticos de este complejo y de otros grupos relacionados. Las preferencias de hábitat altamente localizadas y especializadas de esta nueva especie son motivo de gran preocupación por su conservación.

REDISCOVERY OF A CRYPTIC SPECIES AND DESCRIPTION OF A NEW SUBSPECIES IN THE MYRMECIZA HEMIMELAENA COMPLEX (THAMNOPHILIDAE) OF THE NEOTROPICS

Abstract The recording in 1992 of an unknown antbird loudsong initiated a journey of discovery that led to the resolution of the conflict between John Zimmer (1932) and Melvin Carriker (1934) regarding the taxonomic standing of the population of Myrmeciza hemimelaena, a widespread southern Amazonian antbird, that occurs in lower Andean elevations in San Martín, Peru. Zimmer had described a new subspecies, M. h. castanea, from the Moyobamba Valley, but Carriker, on the basis of specimens he collected at the same elevation in an adjoining valley, could not find morphological differences between his specimens and the widespread nominate form of M. hemimelaena. Both authors were correct. Two cryptic sister taxa coexist in the foothills of San Martín. Diagnostic vocal and morphological characters and syntopy confirm their status as distinct species. Myrmeciza hemimelaena castanea Zimmer is revived and raised to species status. Concurrently, analysis of the vocalizations and morphology of the lowland population north of the Río Marañón in Peru, the loudsong recording of which initiated the project, revealed that this population was closely related to M. castanea of which it is described as a subspecies, M. c. centunculorum, under the biological species concept. The discovery that there are two cryptic species in the Myrmeciza hemimelaena complex exemplifies the continuing need to pursue field knowledge and analysis of avian species limits in the Neotropics required for the development of conservation strategies as well as phylogenetic understanding.

Epinecrophylla, a new genus of antwrens (Aves: Passeriformes: Thamnophilidae)

ABSTRACT We offer a new generic name for the stipple-throated assemblage of antwrens (Thamnophilidae) currently placed in the genus Myrmotherula. Molecular studies demonstrated that Myrmotherula is polyphyletic, with the stippled-throated group forming a clade that is not sister to any other currently recognized Myrmotherula species. The stipple-throated assemblage is distinguished morphologically by at least one sex having a black throat stippled white or buffy white combined with a comparatively long, unmarked tail, although three populations considered subspecies have lost one of these characters. The distinct evolution of this assemblage is supported by diagnostic behavioral characters derived from foraging behaviors, vocal repertoires, and nest architecture.

AN INTEGRATIVE APPROACH TO SPECIES-LEVEL SYSTEMATICS REVEALS THE DEPTH OF DIVERSIFICATION IN AN ANDEAN THAMNOPHILID, THE LONG-TAILED ANTBIRD

Abstract. The geographic range of the Long-tailed Antbird (Drymophila caudata) extends from the Paria Mountains of Venezuela south through the Andes to northern Bolivia, a geographic and elevational distribution unique in the antbirds (Thamnophilidae). Plumage variation among most populations is not obvious, and although eight subspecies have been described, half have been synonymized. We took a multidimensional approach to reexamining the taxonomy of the complex. We identified lineages by evaluating divergence in mtDNA, and defined study groups within them to take into account previously described plumage differences. We then assessed the taxonomic status of principal lineages and study groups by comparing vocal differences among them to established taxonomic “yardsticks” for thamnophilid antbirds. Finally, we related taxa to the ecology of the regions in which they occur. The outcomes revealed substantial diversification, sufficient for recognition of four species, three restricted to the north and one widespread along the main body of the Andes extending from northwestern Colombia south to Bolivia. Speciation in Andean Drymophila antbirds is partially associated with elevational and environmental divergence. The results provide valuable inputs to mapping and understanding avian evolution in the Andes and demonstrate the value of a multifaceted approach in solving taxonomic problems.

Species Limits in Antbirds (Thamnophilidae): The Scale-Backed Antbird (Willisornis poecilinotus) Complex

Abstract The geographic range of the Scale-backed Antbird (Willisornis poecilinotus) encompasses Amazonia. Seven currently defined subspecies are distinguished from one another by diagnostic plumage characters except for one pair. Six pairs of subspecies are apparently parapatric and lack a known barrier to intergradation in at least a portion of their contact zone; yet confirmed hybrids are known only for one pair in one location. An analysis of >350 recordings, however, found vocal differences among them insufficient to recommend elevating subspecies to the species level with one exception. Populations in southeastern Amazonia should be considered a distinct species, Willisornis vidua (Hellmayr), Xingu Scale-backed Antbird, on the basis of their distinct loudsongs, raspy call series, and contact calls. Within the widespread Willisornis poecilinotus, Common Scale-backed Antbird, the remaining instances of parapatry without extensive intergradation provide a focus for future fieldwork to define interrelationships in contact zones and mechanisms of species recognition that may be sustaining them on independent evolutionary paths.

SPECIES LIMITS IN THE “SCHISTOCICHLA”COMPLEX OF PERCNOSTOLA ANTBIRDS (PASSERIFORMES: THAMNOPHILIDAE)

Abstract The species-group in the genus Percnostola that is sometimes placed in the genus “Schistocichla” is shown to consist of seven, mostly allopatric, species. All seven are distinct morphologically; when their vocalizations were compared, 19 of 21 pairwise comparisons resulted in differences as great as or greater than those of syntopic species-pairs in this family. Differences in the two remaining comparisons were limited to two vocal characters, but one involved a pair whose ranges appear to abut without apparent physical barriers; members of the second pair were separated geographically by ∼2,400 km. Insights into speciation in the complex are relevant to conservation efforts and ultimately will be related to an ongoing genetic study to suggest a phylogeny and contribute to an understanding of avian evolution in Amazonia.

SPECIES LIMITS IN ANTBIRDS: THE THAMNOPHILUS PUNCTATUS COMPLEX CONTINUED

Abstract In a previous study (Isler et al. 1997) we examined species limits in the Thamnophilus punctatus complex of the Neotropics. We recommended that six taxa be considered species, but were unable to make recommendations regarding two morphologically distinct and geographically restricted taxa, leucogaster and huallagae, due to the lack of vocal recordings which were essential to our methodology. Analysis of newly obtained recordings has found that vocal differences support the separation at the species level of leucogaster and huallagae from five of the six species in the complex (T. atrinucha, T. stictocephalus, T. sticturus, T. pelzelni, and T. ambiguus). However, leucogaster and huallagae could not be distinguished vocally from each other nor from nominate punctatus to an extent that supported species status, and they are retained as subspecies under our recommended guidelines (Isler et al. 1998, 1999). The Thamnophilus punctatus complex affords an interesting opportunity for future molecular studies that compare the genetic distances among populations that have differentiated vocally and those that have not. The question of species status of leucogaster and huallagae is pressing because the ranges of both taxa are limited to sub-Andean basins in northwestern Peru and southwestern Ecuador that increasingly are under cultivation.