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The availability of small, lightweight tracking devices enhances our ability to study birds during mobile phases of their lives. Tree Swallows Tachycineta bicolor, a model species of wild songbird, are well-studied during their breeding season; but our understanding of their biology at other times of the year, when they are not tied to the fixed location of a nest, is more limited. We developed a lightweight radio tag with no battery (solar nanotag) to study the movements of small animals, and we deployed it to explore the behavior of Tree Swallows after the end of their summer breeding season. We tagged 32 breeding adult swallows and 36 juveniles and monitored their presence and absence at the breeding site during the post-fledging period. Although our observations are based on very small sample sizes, the tags revealed previously unknown patterns in Tree Swallow behavior during the post-breeding season. Some Tree Swallow fledglings continued to visit the site repeatedly in the months following the nesting season, with the latest detection occurring on September 30th; by contrast, all adults had permanently departed by the end of July. These results inform future hypotheses about post-breeding movements in Tree Swallows. But, more generally, the detection of tagged swallows on their distant wintering grounds, seven months after tagging, indicates the potential of studying small passerine movements throughout their entire lifetimes, and suggests a rich array of applications for these \"Life Tags\" to study the movements of small animals world-wide.

We used high precision computed tomography (CT) and traditional radiography to study the nasal conchae, complex structures within the nasal cavity that condition air via countercurrent heat exchange. Air conditioning in the conchae assists thermoregulation and water balance, both of which pose challenges for many birds. We hypothesized that hot and water-limited environments would select for larger or more complex conchae to maximize moisture recapture during exhalation and in turn cause the evolution of deeper and wider bills. We provide the first intraspecific comparison of concha size and structure in birds based on CT scans of 15 individuals and radiographs of 39 individuals of 2 subspecies of Song Sparrow (Melospiza melodia) that inhabit climatically distinct habitats. CT scans revealed that middle and rostral conchae filled the nasal cavities and had larger surface areas in individuals with larger nasal cavities. The subspecies that inhabits hot and dry coastal dunes (M. m. atlantica) had relatively larger conchae and greater overlap of middle and rostral conchae than a nearby inland subspecies that inhabits moister environments (M. m. melodia). Radiographs revealed deeper and wider nasal cavities in the dune-endemic subspecies, further indicating they have larger conchae. Locations of maximum complexity of both conchae were more distal in the dune endemic subspecies. These anatomical differences suggest current or past divergent selection pressures on conchae; the larger conchae in the dune subspecies may allow greater water recapture while exhaling. The conchae and external bill are nested structures that were positively related in size and play functionally related roles in thermoregulation, therefore suggesting phenotypic integration. We hypothesize that the typically deeper and wider bill of the dune subspecies has evolved, at least in part, to accommodate larger conchae.

Nest predation has driven the evolution of specialized behaviors that decrease the probability that a predator encounters a nest. We collected descriptions from the literature of a behavior wherein male and female adults fly to their nest as a pair, with one bird flying onward or veering off while the other enters the nest. We suggest that the most likely function of this behavior is to decrease the risk of nest predation from visual nest predators. In this hypothesis, visual nest predators are distracted by the flying bird and thus fail to observe the bird arriving to the nest entrance (and the nest itself), although the putative adaptive value of this behavior remains to be confirmed. While this behavior has been sporadically noted in the natural history literature, few ornithologists are aware it is found across multiple taxa, especially in the Neotropics. We show that this behavior occurs in at least 28 species across 5 distinct families (and 11 genera) of passerines. We propose a classification scheme for this and similar behaviors and discuss factors hypothesized to promote the evolution of this behavior (e.g., mate guarding, building enclosed nests). We call this behavior “coordinated misdirection” (or “desvío coordinado” in Spanish) because it depends on the cooperation of at least 2 birds, and its presumed function is a visual misdirection—a ruse to draw the observers' attention away from the nest. Finally, we encourage future research so that the evolutionary history of the behavior can be explored and the behavior can be analyzed under a life history framework.

Common names of species are important for communicating with the general public. In principle, these names should provide an accessible way to engage with and identify species. The common names of species have historically been labile without standard guidelines, even within a language. Currently, there is no systematic assessment of how often common names communicate identifiable and biologically relevant characteristics about species. This is a particular issue in ornithology, where common names are used more often than scientific names for species of birds in written and spoken English, even by professional researchers. To gain a better understanding of the types of terminology used in the common names of bird species and their frequency of use, we used a crowdsourcing approach and recruited 85 professional ornithologists and non-professional participants to classify unique descriptors in the English-language common names of all recognized bird species from around the world. Each species' common name was assigned to one of ten categories associated with aspects of avian biology, ecology, or human culture. Across 10,906 species of birds, 89% have names describing the biology of the species, while the remaining 11% of species have names derived from human cultural references or local non-English languages. Species with common names based on features of avian biology are more likely to be related to each other or be from the same geographic region. The crowdsourced data collection also revealed that many common names contained specialized or historic terminology unknown to many of the data collectors, and this was documented in a glossary and gazetteer alongside the dataset. As the first comprehensive assessment of the state of terminology in English-language common names of birds, the AvianLexiconAtlas database sheds light on historical approaches to nomenclature and provides insight into how the general public currently engages with species through their names.Competing Interest StatementThe authors have declared no competing interest.Footnotes* The title, abstract, introduction, and conclusion have been updated to present the new dataset, glossary, and gazetteer produced during this research as a research database, now called the AvianLexiconAtlas. Researchers from across academic fields can use the resources in this database to study the history of English-language bird names from a quantitative perspective. In the text we clarify the utility of this database as a resource, but have not changed any of the methods, analyses, figures, or supplemental files.* https://github.com/ajshultz/AvianLexiconAtlas

Animals that engage in long-distance seasonal migration experience strong selective pressures on their metabolic performance and life history, with potential consequences for molecular evolution. Species with slow life histories typically show lower rates of synonymous substitution (dS) than “fast” species. Previous work has suggested that long-distance seasonal migrants have a slower life history strategy than short-distance migrants, raising the possibility that rates of molecular evolution may covary with migration distance. Additionally, long-distance migrants may face strong selection on metabolically important mitochondrial genes owing to their long-distance flights. Using over 1000 mitochondrial genomes, we assessed the relationship between migration distance and mitochondrial molecular evolution in 39 boreal-breeding migratory bird species. We show that migration distance correlates negatively with dS, suggesting that the slow life history associated with long-distance migration is reflected in rates of molecular evolution. Mitochondrial genes in every study species exhibited evidence of purifying selection, but the strength of selection was greater in short-distance migrants, contrary to our predictions. This result may indicate selection for cold tolerance on mitochondrial evolution among species overwintering at high latitudes. Our study demonstrates that the pervasive correlation between life history and molecular evolutionary rates exists in the context of differential adaptations to seasonality.