Sobre-veraneo de Calidris canutus rufa (Charadriiformes: Scolopacidae) en laguna La Picasa, Santa Fe, Argentina

Calidris canutus rufa es una ave playera que tiene su área de reproducción en el Ártico canadiense, y ha sufrido una drástica declinación desde principios de este milenio, con tendencia decreciente de su población. En el verano austral migra al sur de Sudamérica donde tiene una de las áreas principales de descanso no reproductivo, en la Isla Grande de Tierra del Fuego. Es conocido que la especie sobre veranea en las costas de la provincia de Buenos Aires, Argentina, sin reportes para el interior continental del país. A partir del avistamiento de Calidris canutus rufa en la laguna La Picasa, al sur de la provincia de Santa Fe, se realizaron muestreos semanales para registrar su presencia durante el invierno austral en este humedal. Se obtuvieron registros de la especie entre julio y septiembre de 2021 en la costa oeste de la laguna. Se trató de ejemplares con plumaje básico, con coloración gris cenicienta en dorso y blanca ventral, flancos barrados y patas verdosas. Este sería el primer registro de Calidris canutus rufa sobre veraneando en laguna La Picasa, humedal del interior continental de Argentina, en el invierno austral 2021.

Global flyway evolution in red knots Calidris canutus and genetic evidence for a Nearctic refugium

Present-day ecology and population structure are the legacies of past climate and habitat perturbations, and this is particularly true for species that are widely distributed at high latitudes. The red knot, Calidris canutus, is an arctic-breeding, long-distance migratory shorebird with six recognized subspecies defined by differences in morphology, migration behavior, and annual-cycle phenology, in a global distribution thought to have arisen just since the Last Glacial Maximum (LGM). We used nextRAD sequencing of 10,881 single-nucleotide polymorphisms (SNPs) to assess the neutral genetic structure and phylogeographic history of 172 red knots representing all known global breeding populations. Using population genetics approaches, including model-based scenario-testing in an approximate Bayesian computation (ABC) framework, we infer that red knots derive from two main lineages that diverged ca. 34,000 years ago, and thus persisted at the LGM in both Palearctic and Nearctic refugia, followed by at least two instances of secondary contact and admixture. In two flyways, we detected clear genetic structure between population pairs with similar migrations and substantial geographic overlap in the non-breeding season. Conversely, other populations were only weakly differentiated despite clearly divergent migratory phenotypes and little or no apparent contact throughout the annual cycle. In general, the magnitude of genetic differentiation did not match that of phenotypic differences among populations, suggesting that flyway-specific phenotypes developed quite rapidly and do not necessarily impose barriers to gene flow. Our results suggest that population structure and migratory phenotypes in red knots arose from a complex interplay among phylogeography, plasticity, and selective processes.

Insights into migratory connectivity and conservation concerns of Red Knots Calidris canutus in the austral Pacific coast of the Americas

Summary Migratory species rely on several distant sites during the annual cycle which makes their conservation more complex than that of non-migratory species. Even one of the most extensively studied migratory shorebirds - the Red Knot Calidris canutus - is currently ‘Near Threatened’ at the global level. Conflicting observations of migratory routes cast uncertainty on the subspecies classification and migratory connectivity of Red Knots in the Pacific coasts of the Americas. To fill essential information gaps, we present the first detailed population morphometrics of Red Knots during the non-breeding season in the southern Pacific coast, along with resightings of these birds throughout the Americas. We also estimated daily rate of weight gain during fuelling based on body mass at captures and known departure dates. Resightings demonstrate reliance on staging areas in both the Mid-continental and Atlantic flyways during the northward migration, and additionally in the Pacific Flyway during southward migration. In addition to the strong connection with several areas also used by C. c. rufa on the North American Atlantic coast, our results show morphometric differences within the ranges of both C. c. rufa and C. c. roselaari. Given the threats faced by Red Knots, the population in Chiloé Archipelago should be treated as a separate conservation unit within interhemispheric conservation programmes for endangered shorebirds within the Americas.

Red knots (Calidris canutus islandica) manage body mass with dieting and activity

ABSTRACTMass regulation in birds is well documented. For example, birds can increase body mass in response to lower availability and/or predictability of food and decrease body mass in response to increased predation danger. Birds also demonstrate an ability to maintain body mass across a range of food qualities. Although the adaptive significance of mass regulation has received a great deal of theoretical and empirical attention, the mechanisms by which birds achieve this have not. Several non-exclusive mechanisms could facilitate mass regulation in birds. Birds could regulate body mass by adjusting food intake (dieting), activity, baseline energetic requirements (basal metabolic rate), mitochondrial efficiency or assimilation efficiency. Here, we present the results of two experiments in captive red knots (Calidris canutus islandica) that assess three of these proposed mechanisms: dieting, activity and up- and down-regulation of metabolic rate. In the first experiment, knots were exposed to cues of predation risk that led them to exhibit presumably adaptive mass loss. In the second experiment, knots maintained constant body mass despite being fed alternating high- and low-quality diets. In both experiments, regulation of body mass was achieved through a combination of changes in food intake and activity. Both experiments also provide some evidence for a role of metabolic adjustments. Taken together, these two experiments demonstrate that fine-scale management of body mass in knots is achieved through multiple mechanisms acting simultaneously.