Juan Ignacio Areta

Phylogeny and Taxonomy of the Patagonian Miocene Falcon Thegornis musculosus Ameghino, 1895 (Aves: Falconidae)

Abstract The fossil record of the family Falconidae is poor and fragmentary. Extinct representatives from South America include the late early Miocene (Santacrucian) Thegornis musculosus and Thegornis debilis. Both species were originally described as Falconidae and afterwards moved to Accipitridae Circinae or Buteoninae. The analysis of a very well preserved and complete specimen of T. musculosus with similar stratigraphic and geographic provenances of the type material (lower levels of Santa Cruz Formation, coast of Patagonia, Argentina) corroborates the validity of the genus and its falconid affinities. The skull and postcranial morphology exhibit strong resemblances with the open-savannah inhabiting Herpetotheres and the forest-dwelling Micrastur (Herpetotherinae) but differ substantially from Falconinae (Falconini plus Caracarini). Detailed comparisons with a broad arrange of falconiform taxa in a cladistic framework, confirm its phylogenetic placement within the Herpetotherinae and sister to H. cachinnans. The ecotonal margins produced by the vanishing of humid forests that developed during changes in Patagonian plant communities throughout early Neogene times are hypothesized as a plausible scenario to understand the evolution of this basal clade of falcons.

Using Species Distribution Modeling to Assess Factors that Determine the Distribution of Two Parapatric Howlers (Alouatta spp.) in South America

Through presence-only data, ecological niche modeling can use environmental variables to generate maps of areas that are potentially suitable for the presence of a species, improving our knowledge of its niche requirements and extending our understanding of its geographic distribution. We used the ecological niche model MaxEnt to predict the potential distribution of black-and-gold howlers (Alouatta caraya) and brown howlers (Alouatta guariba clamitans) in South America, as well as the potential sympatry area between both species. We modeled distributions of Alouatta caraya (196 presence localities, 8 bioclimatic variables) and A. guariba clamitans (74 presence localities, 13 bioclimatic variables) using bioclimatic variables from WorldClim with habitat suitability categorized as low, moderate, or high. Alouatta caraya showed a broader potential distribution, occupying a wide variety of habitats in a broad range of temperatures. Temperature annual range (Bio 7) was the bioclimatic variable with most influence in modeling the potential distribution of this species. Alouatta guariba clamitans was more restricted to rainy areas of mature forests at higher altitudes with low minimum temperatures. Mean temperature of coldest quarter (Bio 11) was the bioclimatic variable with the highest influence in this model. The predicted area of potential sympatry of both species was a relatively small area in the interior Atlantic Forest ecoregion, and a new syntopy locality occurred within the predicted area of sympatry. This narrow zone of overlap could be maintained, among other causes, by the role of the Paraná River as a natural barrier for dispersion, differences in niche requirements, potential interspecific competition, and hybridization.

Breeding biology and conservation of the Marsh Seedeater Sporophila palustris

Summary The Marsh Seedeater Sporophila palustris is one of the most endangered and least known of the capuchino seedeaters. Breeding populations are patchy, occurring in north-east Argentina, southern Brazil, and Uruguay. We present data on the breeding biology of the species, and describe nests and eggs, behaviour (including courtship, nesting, incubation and parental care), breeding sites and food items. Marsh Seedeaters breed in well-preserved grasslands with wet soils and tall vegetation. In general, these habitats are used for extensive livestock ranching. Main threats are overgrazing, widespread use of fire, conversion of grasslands to pastures of exotic grasses and rice fields, afforestation, and illegal trapping. Most breeding sites are located in Important Bird Areas, but only one in Brazil and one in Argentina are protected. We propose a series of actions to promote the conservation of Marsh Seedeaters and other endangered birds that coexist in grassland habitats. Resumen El Capuchino Pecho Blanco Sporophila palustris es uno de los capuchinos menos conocidos y uno de los mas amenazados. Sus poblaciones reproductivas son locales, fragmentadas y ocurren en el nordeste de Argentina, sudeste de Brasil y en Uruguay. Presentamos datos reproductivos describiendo nidos y huevos, comportamiento (incluyendo cortejo, nidificacion, incubacion y cuidado parental), sitios de anidacion y datos sobre alimentacion. El Capuchino Pecho Blanco nidifica en pastizales altos y humedos en buen estado de conservacion. Estos habitats en general se han convertido en areas ganaderas. Las principales amenazas son sobrepastoreo, uso generalizado del fuego, drenaje de humedales, reemplazo total del habitat por pasturas y forestaciones y captura ilegal. La mayoria de los sitios se localizan en AICAs, pero solo uno en Brasil y otro en Argentina se encuentran protegidos. Finalmente, proponemos una serie de medidas que contribuyen a la preservacion del Capuchino Pecho Blanco y de otras aves amenazadas que conviven con este.

Tiny Bird, Huge Mystery—The Possibly Extinct Hooded Seedeater (Sporophila melanops) Is a Capuchino with a Melanistic Cap

Known with certainty solely from a unique male specimen collected in central Brazil in the first quarter of the 19th century, the Critically Endangered (Possibly Extinct) Hooded Seedeater Sporophila melanops has been one of the great enigmas of Neotropical ornithology, arguably the only one of a host of long-lost species from Brazil to remain obstinately undiscovered. We reanalysed the morphology of the type specimen, as well as a female specimen postulated to represent the same taxon, and sequenced mitochondrial DNA (COI and Cyt-b) from both individuals. Furthermore, we visited the type locality, at the border between Goiás and Mato Grosso, and its environs on multiple occasions at different seasons, searching for birds with similar morphology to the type, without success. Novel genetic and morphological evidence clearly demonstrates that the type of S. melanops is not closely related to Yellow-bellied Seedeater S. nigricollis, as has been frequently postulated in the literature, but is in fact a representative of one of the so-called capuchinos, a clade of attractively plumaged seedeaters that breed mostly in the Southern Cone of South America. Our morphological analysis indicates that S. melanops has a hitherto unreported dark-coffee throat and that it is probably a Dark-throated Seedeater S. ruficollis collected within its wintering range, acquiring breeding plumage and showing melanism on the cap feathers. Alternatively, it may be a melanistic-capped individual of a local population of seedeaters known to breed in the Esteros del Iberá, Corrientes, Argentina, to which the name S. ruficollis might be applicable, whilst the name S. plumbeiceps might be available for what is currently known as S. ruficollis. A hybrid origin for S. melanops cannot be ruled out from the available data, but seems unlikely. The purported female specimen of S. melanops pertains either to S. nigricollis or to Double-collared Seedeater S. caerulescens based on genetic and morphological data, and thus cannot be a female of S. melanops. We conclude that Sporophila melanops is not typical of any natural population of seedeaters, appears to have been collected far from its breeding grounds while overwintering in central Brazil, and should not be afforded any conservation status.

Ontogeny of long-range vocalizations in a Neotropical fossorial rodent: the Anillaco Tuco-Tuco (Ctenomys sp.)

Tuco-tucos (Ctenomys spp.) are subterranean rodents that produce territorial, high intensity long-range vocalizations (LRVs) of broadband and low frequency that are essential for long-distance communication between individuals in different tunnel systems. Despite their importance, the development of LRVs remains poorly understood. In adult Anillaco Tuco-Tucos (Ctenomys sp.) the LRV is composed by two types of syllables (series and individual notes) that are repeated a variable number of times. We studied the development of the LRVs in eight juveniles of the Anillaco Tuco-Tuco ranging from 14–28 to 104–118 days after birth. We (1) tested whether the syllables followed any of three alternative developmental modes (retention of juvenile vocalizations, modification of juvenile precursors or de novo appearance in adults), (2) evaluated the development of structural and acoustic features of syllables, and (3) tested the prediction that juveniles should produce a greater proportion of atypical series in precursors of the LRV than adults, due to lack maturation and/or precise coupling of neuromuscular and anatomical structures. The LRV of the Anillaco Tuco-Tuco exhibited a mixed developmental mode: while series developed from juvenile precursors whose acoustic features gradually approached those of adults, individual notes appeared later in the ontogeny and de novo with acoustic features indistinguishable from those of adults. The number of series per vocalization increased through development and varied from one to 25 in juvenile males and from one to six in juvenile females. The structure of the most common series type (triad) did not exhibit ontogenetic changes and was present as such at the onset of the emission of vocalizations. On the contrary, acoustic features of juvenile triad notes changed with age in both sexes (duration 90% increased through development, while bandwidth 90% and peak frequency decreased). Furthermore, juveniles emitted a higher proportion of atypical series than adults (7.4% vs. 0.3%), as expected in the development of any complex behavior that requires practice to be mastered. The maturation of the LRV occurred well before the sexual maturation, presumably due to the protracted time needed to acquire or build a burrow system long before mating is possible. We propose that protracted vocal development is another component in the slow developmental strategy of Ctenomys and subterranean rodents in general.

Ecological segregation and vocal interactions in two sympatric Laterallus crakes

AbstractEcological segregation and interspecific territoriality can reduce exploitative competition in morphologically and ecologically very similar species allowing their coexistence. We studied habitat use and features, ecomorphology and homo- and heterospecific playback responses in the similar and sympatric Red-and-white Crake (Laterallus leucopyrrhus) and Rufous-sided Crake (Laterallus melanophaius) on the coast of the Río de la Plata, Argentina. We carried out playback sessions with stimuli of both crakes in four habitat types potentially used by them across the four seasons (coastal humid scrub, bulrush, floodable grassland and exotic yellow iris). Crakes were segregated year-round by habitat, with minor overlap: Red-and-white Crakes used bulrush, while Rufous-sided Crakes used coastal humid scrub. Patterns of habitat use were the same when using homo- or heterospecific playback stimuli, and both species responded similarly to homo- and heterospecific playback trials in their selected habitats. Crakes were morphologically distinct and some of their differences can be related to habitat features and resource exploitation: Red-and-white Crakes had longer tarsi and “blunt” bills and inhabited the deeper and denser bulrush, while Rufous-sided Crakes had shorter tarsi and “dagger” bills and inhabited the shallower and more open coastal humid scrub. Habitat use resulting in spatial segregation in these crakes seems to be more related to specific abilities to exploit different habitats than to interspecific competition or interspecific territoriality. Habitat adaptation would be more relevant within large patches of homogeneous and simple habitats selected by each Crake, while interspecific territoriality would gain importance at habitat boundaries with heterogeneous or intermediate conditions.ZusammenfassungÖkologische Trennung und vokale Interaktionen zweier sympatrischer Rallen (Laterallus) Ökologische Trennung und interspezifisches Territorialverhalten können ausbeuterische Konkurrenz bei morphologisch und ökologisch sehr ähnlichen Arten verringern und damit deren Koexistenz ermöglichen. Wir untersuchten die Habitat-Besonderheiten und dessen Nutzung, die Ökomorphologie und die homo- und hetero-spezifischen Playback-Antworten bei den sehr ähnlichen und sympatrischen Arten Weißbrustralle (Laterallus leucopyrrhus) und Rothalsralle (L. melanophaius) am Rio de la Plata, Argentinien. Dafür führten wir Playback-Sitzungen mit vokalen Stimuli beider Rallenarten und in denjenigen vier Habitat-Typen durch, die von den beiden Arten über die vier Jahreszeiten genutzt werden (feuchte Küsten-Macchia, Binsen und Schilf, regelmäßig überflutetes Grasland und Wasserschwertlilien). Die Rallen blieben rund ums Jahr mit nur kleinen Ausnahmen durch die Habitate voneinander getrennt: die Weißbrustrallen nutzten Binsen und Schilf, die Rothalsrallen die feuchte Küsten-Macchia. Die Art und Weise der Habitat-Nutzung blieb gleich, egal ob homo- oder heterospezifische Playback-Reize gegeben wurden, und beide Arten antworteten auf ähnliche Weise auf homo- und heterospezifische Playbacks in ihren jeweiligen Habitaten. Die Rallen sind morphologisch klar unterschiedlich, wobei einige Unterschiede auf die unterschiedlichen Habitat-Eigenschaften und Resourcen-Nutzung zurückgeführt werden können: die Weißbrustrallen haben längere Tarsi und stumpfe Schnäbel und leben im tieferen und dichteren Schilfdickicht, wohingegen die Rothalsrallen kürzere Tarsi und schärfere Schnäbel haben und die flachere und offenere Küsten-Macchia bewohnen. Ihre Habitat-Nutzung und die sich daraus ergebende räumliche Trennung scheinen bei beiden Rallen-Arten mehr von den jeweiligen Fähigkeiten abzuhängen, unterschiedliche Habitate zu nutzen als von interspezifischer Konkurrenz oder Territorialität. Eine Anpassung an ein Habitat wäre eher bei großen, zusammenhängenden Habitaten relevant, die sich jeweils eine Rallen-Art aussuchen würde, wohingegen interspezifisches Territorialverhalten dann eine Bedeutung hätte, wenn die Habitatgrenzen sehr heterogen wären oder es ausgeprägte Übergänge zwischen den Habitaten gäbe.

Mate recognition systems and species limits in a warbling-finch complex (Poospiza nigrorufa/whitii)

ABSTRACT Species limits in the Poospiza nigrorufa/whitii complex are not well understood. Three taxa formally described as species are now considered as subspecies (nigrorufa, whitii and wagneri) of a widespread species. The heavier nigrorufa has longer bill, tarsus and wings, is slightly dimorphic with males showing tawny rufous throat, breast and flanks, and brownish grey upper parts with a slate tinge, while females differ in the orange tinge of ventral parts and in the more olivaceous upper parts; inhabits shrubby open areas and wetlands with reeds and bulrushes in eastern southern South America, and gives a simple three-note pattern that repeats to form the song and diagnostic calls. The lighter whitii (including wagneri as a synonym) has a shorter bill, tarsus and wings, is highly dimorphic with males having dark chestnut throat, breast and flanks, and slate upper parts, while females exhibit tawny pale-orange ventral parts, and olivaceous light-brown upper parts; inhabits closed to semi-closed xerophytic to semi-humid scrub and woodlands in the western highlands, and has a complex multi-noted song and diagnostic calls. Reciprocal playback experiments indicate that both taxa are able to discriminate each other’s songs. Locality data and ecological niche modelling show that nigrorufa and whitii are narrowly allopatric or parapatric in central Córdoba province (Argentina).This integrative evidence and the ~2.5% divergence in mtDNA show that nigrorufa and whitii possess different Specific Mate Recognition Systems and should be afforded full species status under any species concept.

Mixing the waters: a linear hybrid zone between two riverine Neotropical cardinals (Paroaria baeri and P. gularis)

ABSTRACT Amazonian rivers have been more frequently conceptualised as barriers rather than as habitats for birds with their own ecological and biogeographic histories. However, many river-restricted bird species have differentiated within the formidable network formed by the Amazon and its tributaries. Here we demonstrate that the riverine-distributed Crimson-fronted Cardinal (Paroaria baeri) is narrowly distributed along the middle Rio Araguaia basin, where it comes into contact and hybridises with the geographically widespread Red-capped Cardinal (P. gularis). This one-dimensional hybrid zone, which is situated over ca.160 km along the Araguaia and Javaés Rivers, appears to be of recent origin. Admixed individuals between the non-sister P. baeri and P. gularis are phenotypically intermediate between the parental species, and superficially resemble the geographically disjunct and phylogenetically distant Masked Cardinal (P. nigrogenis). Two phenotypically admixed specimens were confirmed as such based on sequences of the mitochondrial Cytb and the Z-linked MUSK gene. Field observations and genetic data indicate that P. baeri × P. gularis hybrids are capable of producing viable offspring, but more data are necessary to confirm hybrid viability and fertility. The non-sister hybridising species P. baeri and P. gularis last shared a common ancestor 1.8–2.8 mya (uncorrected genetic p-distance of 4%), which corresponds closely to when the Araguaia/Tocantins river basin last discharged directly into the Amazon.