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The literature on mixed-species flocks references a wide variety of bird associations. These studies, however, have used an array of unstructured characteristics to describe flocks, ranging from the temporal occurrence of flocking to the identity and behavioural features of constituent members, with little consensus on which key traits define and characterize a mixed-species flock. Moreover, although most studies report species-specific roles, there is no clear consensus about what these roles signify nor how to define them. This lack of consistency limits our ability to compare flocks from different habitats, regions and species pools. To unify this sizable body of literature, we reviewed and synthesized 538 studies on mixed-species flocks. We propose 13 categories to classify mixed-species flocks using behavioural and physical traits at the flock and participant level, as well as the habitat where the flock occurs. Lastly, we discuss the historical terminology for different species roles and propose definitions to clarify and distinguish among nuclear, leader, sentinel, and flock-following species. We envision that these guidelines will provide a universal language for mixed-species flock research, paving the way for future comparisons and new insight between different regions and systems. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Mixed-species flocks of birds involve species with different roles and foraging strategies and are ubiquitous in forest environments. Species roles can broadly be categorized into leaders who attract other to form the flock, as well as lead the flock’s movement; and follower species. The diversity of foraging strategies occurring in a mixed flock reflects the diversity of participant species. One of the main benefits of participating in mixed-species flocks is increased foraging efficiency. However, feeding benefits remains under debate probably because not all participants receive this benefit in the same way. For instance, leaders and followers may benefit differentially, and particular foraging strategies might additionally influence feeding benefits. To identify leader species and evaluate foraging benefits in relation to species roles and foraging strategies, we conducted 375-h of surveys in subtropical Andean-foothill forests across three years. We recorded species leading the movement of the flocks and the foraging efficiency of the constituent birds. Because leader behaviour is related to the ability to attract other participants, we developed a standardized network analysis that helped us to identify them. We tested and compared whether behavioural leaders presented a higher topological position of dominance within the network. We found thirty-five species behaving like leaders; most could change from leaders to followers depending on the flock composition. The most frequent leader species had a higher topological dominance in the network. The foraging efficiency of leader and follower species inside mixed flocks increased compared to birds outside them. To some extent, the foraging efficiency of birds inside mixed flocks depended on their primary foraging strategy. Foliage Invertivore and Frugivore-Invertivore species tended to increase their foraging efficiency while Bark Invertivore, Aerial Invertivore, and Granivore-Invertivore species did not show changes in their foraging efficiency in flocks. Although the general trend among mixed flocks participants was to increase their foraging efficiency, exceptions suggest that other benefits come into play, such as predator avoidance or feeding on more profitable prey items. Our study indicates that benefits gained from foraging in mixed flocks depend on a complex combination of species roles, species-specific traits, and facilitation mechanisms linked to the primary foraging strategy of bird species. Mixed-species flocks of birds involve species with different roles and foraging strategies and are ubiquitous in forest environments. Species roles can broadly be categorized into leaders who attract other to form the flock, as well as lead the flock’s movement; and follower species. The diversity of foraging strategies occurring in a mixed flock reflects the diversity of participant species. One of the main benefits of participating in mixed-species flocks is increased foraging efficiency. However, feeding benefits remains under debate probably because not all participants receive this benefit in the same way. For instance, leaders and followers may benefit differentially, and particular foraging strategies might additionally influence feeding benefits. To identify leader species and evaluate foraging benefits in relation to species roles and foraging strategies, we conducted 375-h of surveys in subtropical Andean-foothill forests across three years. We recorded species leading the movement of the flocks and the foraging efficiency of the constituent birds. Because leader behaviour is related to the ability to attract other participants, we developed a standardized network analysis that helped us to identify them. We tested and compared whether behavioural leaders presented a higher topological position of dominance within the network. We found thirty-five species behaving like leaders; most could change from leaders to followers depending on the flock composition. The most frequent leader species had a higher topological dominance in the network. The foraging efficiency of leader and follower species inside mixed flocks increased compared to birds outside them. To some extent, the foraging efficiency of birds inside mixed flocks depended on their primary foraging strategy. Foliage Invertivore and Frugivore-Invertivore species tended to increase their foraging efficiency while Bark Invertivore, Aerial Invertivore, and Granivore-Invertivore species did not show changes in their foraging efficiency in flocks. Although the general trend among mixed flocks participants was to increase their foraging efficiency, exceptions suggest that other benefits come into play, such as predator avoidance or feeding on more profitable prey items. Our study indicates that benefits gained from foraging in mixed flocks depend on a complex combination of species roles, species-specific traits, and facilitation mechanisms linked to the primary foraging strategy of bird species.

The confusing taxonomic history of Rough-legged Tyrannulet (Phyllomyias burmeisteri) casts doubt on whether a nest and egg from Brazilian Atlantic Forest might instead belong to the Greenish Tyrannulet (Phyllomyias virescens). A nest of P. burmeisteri placed 7.6 m.-up on a horizontal fork in a secondary horizontal branch of Myroxylon peruiferum in late December 2013 in the Yungas of Argentina was a relatively large cup lined and covered with green "old-man's beard" in the upper outer rim, with abundant relatively large flakes of foliar lichens on the sides. Another nest found in early September 1995 in the Atlantic Forest of Paraguay was a cup made of twigs, roots and covered in lichen, placed c.20 m.-up on a horizontal bough. These nests resembled that reported by Ihering. Usage of cup-shaped nests to establish phylogenetic relationships is limited by their simplicity and the lack of detailed descriptions.

Este trabalho tem como objetivo avaliar como a geografia territorial da Rota de Integração Latino-Americana contribui para a construção e a formatação de roteiro para o turismo de observação de aves, com enaltecimento de paisagens, de práticas culturais, de territorialidades e da sociobiodiversidade como um todo representadas na Rota. A área de estudo envolve municípios brasileiros, paraguaios, argentinos e chilenos atingidos diretamente por esse Corredor Rodoviário. O território abarcado pela Rota de Integração Latino-Americana é contemplado por vários ambientes propícios para a prática do turismo de observação de aves, em especial aqueles contemplados por Áreas Protegidas e arredores. O roteiro proposto percorre diferentes topografias, ecorregiões e ecossistemas singulares da América do Sul, tais como: Cerrado, Pantanal, Mata Atlântica, Chaco (seco e úmido), Yungas, Deserto de Montanhas, Campos de Altitude, Puna, Lagoas Altoandinas, Deserto e Vales desérticos, Costa do Pacífico e Tamarugales. Em cada localidade a biodiversidade compõe o espaço junto das práticas culturais e de territorialidades singulares. Tamanha riqueza e diversidade projeta esse percurso como um excelente roteiro para o turismo de observação de aves, pronto a ser percorrido, contemplado e apreciado em suas múltiplas possibilidades.

A major barrier to advancing ornithology is the systemic exclusion of professionals from the Global South. A recent special feature, Advances in Neotropical Ornithology, and a shortfalls analysis therein, unintentionally followed a long-standing pattern of highlighting individuals, knowledge, and views from the Global North, while largely omitting the perspectives of people based within the Neotropics. Here, we review current strengths and opportunities in the practice of Neotropical ornithology. Further, we discuss problems with assessing the state of Neotropical ornithology through a northern lens, including discovery narratives, incomplete (and biased) understanding of history and advances, and the promotion of agendas that, while currently popular in the north, may not fit the needs and realities of Neotropical research. We argue that future advances in Neotropical ornithology will critically depend on identifying and addressing the systemic barriers that hold back ornithologists who live and work in the Neotropics: unreliable and limited funding, exclusion from international research leadership, restricted dissemination of knowledge (e.g., through language hegemony and citation bias), and logistical barriers. Moving forward, we must examine and acknowledge the colonial roots of our discipline, and explicitly promote anti-colonial agendas for research, training, and conservation. We invite our colleagues within and beyond the Neotropics to join us in creating new models of governance that establish research priorities with vigorous participation of ornithologists and communities within the Neotropical region. To include a diversity of perspectives, we must systemically address discrimination and bias rooted in the socioeconomic class system, anti-Blackness, anti-Brownness, anti-Indigeneity, misogyny, homophobia, tokenism, and ableism. Instead of seeking individual excellence and rewarding top-down leadership, institutions in the North and South can promote collective leadership. In adopting these approaches, we, ornithologists, will join a community of researchers across academia building new paradigms that can reconcile our relationships and transform science. Spanish and Portuguese translations are available in the Supplementary Material.

Made available in DSpace on 2022-04-28T17:23:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-02-21 Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina Sociedad de Ornitologia Neotropical - Fondo Francois Vuilleumier para la investigacion de aves neotropicales Lay Summary center dot The theoretical framework used to understand mixed-species flocks formation posits that birds benefit by increasing their foraging efficiency. center dot It follows that birds are more likely to join mixed-species flocks when arthropod abundance decreases. However, we asked, what is the effect of the difficulty in detecting arthropods? center dot We put two ideas into a competition, whether the arthropod abundance or instead their detectability triggers the formation of mixed-species flocks. center dot We have found that the formation of mixed-species flocks is more prone to occur when arthropods are more challenging to find and not necessarily when they are scarcer. center dot We add a new perspective on the drivers of mixed-species flocking, showing that mixed-species flocks' participants achieve higher foraging success and that the capacity to find and recognize prey items may have a more significant effect triggering sociality than prey abundance. Mixed-species flocks presumably provide birds with antipredator and foraging benefits. The foraging benefits hypothesis predicts that a reduction in arthropod abundance will trigger flocking activity; however, flocking activity may also be influenced by the difficulty of detecting arthropods, a seldom explored possibility. We found that environmental traits (temperature and foliage density) combined with arthropod abundance explained arthropod detection by birds in the Yungas foothill forest of NW Argentina. Prey detection was inversely related to ambient temperature and foliage density while positively associated with arthropod abundance. Based on this result, we built a structural equation model using a latent proxy variable for arthropod detectability, arthropod crypsis, integrating ambient temperature, foliage density, and proportion of immature arthropods. This model allowed us to compare the relative importance of arthropod abundance and the difficulty in detecting prey items as predictors of flocking propensity. After 2 yr of studying 129 mixed-species flocks, 1,351 bird foraging sequences, and 25,591 arthropod captures, we found that the flocking propensity of birds was only significantly correlated with arthropod detectability and not with arthropod abundance. Flocking propensity peaked when the arthropod community was comprised of proportionately more immature and non-flying arthropods, the temperature was low, and the foliage cover was denser; all factors are contributing to a low arthropod detectability. Finally, we evaluated whether joining mixed-species flocks provided foraging benefits such as increased foraging efficiency. Individuals benefited from joining flocks by an average increase of their prey-capture attempt rate of 40%, while the search rate increased by 16%. Our results add a new perspective on the drivers of mixed-species flocking by showing that the capacity to find prey items may have a more significant effect than prey abundance per se. Univ Nacl Tucuman UNT, CONICET, Inst Ecol Reg, San Miguel De Tucuman, Argentina UNESP, Dept Ecol, Campus Rio Claro, Rio Claro, SP, Brazil Consejo Nacl Invest Cient & Tecn, Inst Bio & Geociencias Noroeste Argentino, Lab Ecol Comportamiento & Sonidos Nat ECOSON, Salta, Argentina UNESP, Dept Ecol, Campus Rio Claro, Rio Claro, SP, Brazil

Mixed-species flocks of birds have been studied for more than a century, but investigation efforts are historically unbalanced towards certain types of habitats, such as woodlands and lowland forests. Here we provide a first glance of bird flocks' patterns across different gradients in recent studies conducted within the Neotropics. We summarize a symposium where a series of independent studies that approached the topic, some of them making use of techniques that were seldom applied in previous decades in Neotropical systems. We discuss bird flocks' patterns across a latitudinal gradient, social network patterns in bird flocks' across elevational gradients in local and regional scale, and, finally, patterns of flocking response to different levels of human disturbance. Altogether, these studies offer a larger and diverse panorama of possible patterns of response and diversity of mixed-species flocks of birds in the Neotropical region, and provide a rich ground where future studies with bird flocks in the Neotropics may rely on.

It is widely assumed that colonizing species thrive because they lack natural enemies in their new range, increasing their survival and reproductive success. Barn Swallows (Hirundo rustica) started to breed in South America around 1980 and since then have dramatically increased their population size and geographic range, in stark contrast to the decline of the source population in North America. The reasons behind the growth of the South American population are unknown. However, because this species had never bred in this area in recorded times, the lack of natural predators, parasites, or pathogens could lead to higher breeding success, as predicted by the enemy release hypothesis. Here, we test whether breeding success is higher in the newly colonized range than in the native range to test the enemy release hypothesis. We studied the breeding biology of South American Barn Swallows quantifying 7 breeding parameters: clutch size, overall breeding success, offspring mortality by predation and ectoparasites, number of fledglings per breeding attempt, number of breeding attempts per breeding season, and total number of fledglings produced per pair per breeding season. Additionally, we compared these parameters with published information from North American populations using meta-analyses. We found that, while clutch size did not differ between North and South American populations, the southern population overall had lower breeding success, with higher mortality from predation and ectoparasites. An egg laid in South America was 2.6 times more likely to fail than one laid in North America, which resulted on average in 1.1 fewer fledglings per pair per breeding season for the South American breeding population. These results, demonstrating lower breeding success in a newly colonized range, do not support the enemy release hypothesis, and indicate that the growth of the South American Barn Swallow population is most likely caused by other demographic factors. El éxito de colonización de las especies es facilitado por la falta de enemigos naturales en el área colonizada ya que aumenta su supervivencia y éxito reproductivo. Desde que Hirundo rustica ha colonizado Sudamérica alrededor del año 1980, se encuentra en expansión y crecimiento demográfico, en contraste con las tendencias declinantes en su población de origen en Norteamérica. Las razones del crecimiento de esta población son desconocidas. Sin embargo, debido a que la especie nunca antes había nidificado en esta área, la falta de depredadores, parásitos y patógenos naturales podría estar potenciando su éxito reproductivo bajo las predicciones de la Hipótesis de Liberación de Enemigos. En este trabajo testeamos esta hipótesis evaluando si el éxito reproductivo es mayor en el área recientemente colonizada que en la nativa. Estudiamos la biología reproductiva de Hirundo rustica cuantificando siete parámetros reproductivos: tamaño de puesta, éxito de la puesta, mortalidad por depredación, mortalidad por ectoparásitos, número de volantones por nidada, número de nidadas por pareja por temporada y número de volantones por pareja por temporada. Comparamos estos parámetros con los de la especie en Norteamérica utilizando meta-análisis. Encontramos que, a pesar de que ambas poblaciones tienen el mismo tamaño de puesta, la población sudamericana posee un menor éxito reproductivo, con mayor mortalidad por depredación y por ectoparásitos. Un huevo colocado en ésta población posee 2.6 veces la probabilidad de fracasar de uno colocado en la población norteamericana. Resultando en 1.1 menos volantones por pareja al año. Nuestros resultados no soportan la hipótesis de liberación de enemigos, sugiriendo que el crecimiento poblacional de Hirundo rustica en Sudamérica es causado por otro factor demográfico. Fil: Gandoy, Facundo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del Noroeste Argentino. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina Fil: Delhey, Johann Kaspar Valdemar. Monash University; Australia. Max Planck Institute für Ornithologie; Alemania Fil: Winkler, David Ward. Cornell University; Estados Unidos. Cellular Tracking Technologies; Estados Unidos. Conservation Science Global; Estados Unidos Fil: Mangini, Gabriela Giselle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del Noroeste Argentino. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina Fil: Areta, Juan Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del Noroeste Argentino. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina

According to both the predation avoidance and foraging efficiency hypotheses, birds within mixed flocks increase their foraging efficiency and/or can spend more time feeding and less time looking out for predators. These hypotheses predict that birds in mixed flocks obtain benefits. Thus, mixed flock formation could serve as a strategy to cope with difficult conditions imposed on birds such as climatic conditions that ultimately result in a change in predation pressure or food resources. We evaluate the hypotheses that forming part of a flock confers benefits to its members and the associated prediction that birds will take advantage of these benefits and flock more often under cold and dry weather conditions between and within seasons to cope with such conditions. We surveyed the presence of mixed flocks, flocking propensity, number of species and individuals in mixed flocks in the Subtropical Yungas foothill of Argentina, to examine seasonality, flocking behavior of birds and their responses to two climatic variables: temperature and humidity. Bird species presented a higher flocking propensity and mixed flocks occurred more frequently during the dry and cold seasons than during the more benign seasons, and lower values of temperature within seasons triggered the flocking behavior. Although effects between seasons were expected, birds also showed a short-term response to small changes in temperature within seasons. These results strengthen the ideas proposed by the foraging hypothesis. Although benefits derived from flocking have yet to be determined, whatever they are should be understood in the context of seasonal variation in life-history traits. Fil: Mangini, Gabriela Giselle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Areta, Juan Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina

The Alder (Empidonax alnorum) and Willow (E. trailli) flycatchers are cryptic species, and their distribution outside the breeding season is poorly known, owing mostly to identification difficulties. Our new records suggest that large numbers of Alder Flycatchers overwinter in rivers crossing the Chaco region and in the foothill forests of the Yungas of Argentina, significantly increasing their southern wintering range. Records in northern Argentina span 3 November to 23 March. Key habitat for overwintering Alder Flycatchers in Argentina included stands of palo bobo (Tessaria integrifolia) along the Rio Bermejo and tributaries, either in association with sparse shrubs of chilca (Baccharis salicifolia) or more rarely with canebrake (Gynerium sagittatum). Other habitats used were old shrubby ‘madrejones' with Tessaria scrub and sacha cafe (Sesbania virgata), very dense Baccharis salicifolia scrub next to flowing creeks in foothill Yungas and dry Chaco, and riparian forests dominated by palo flojo (...