The major histocompatibility complex (MHC) is a genetic region in jawed vertebrates that contains key genes involved in the immune response. Associations between the MHC and avian malaria infections in wild birds have been observed and mainly explored in the Northern Hemisphere, while a general lack of information remains in the Southern Hemisphere. Here, we investigated the associations between the MHC genes and infections with Plasmodium and Haemoproteus blood parasites along a latitudinal gradient in South America. We sampled 93 rufous‐collared sparrows (Zonotrichia capensis) individuals from four countries, Colombia, Ecuador, Peru, and Chile, and estimated MHC‐I and MHC‐II allele diversity. We detected between 1–4 (MHC‐I) and 1–6 (MHC‐II) amino acidic alleles per individual, with signs of positive selection. We obtained generalized additive mixed models to explore the associations between MHC‐I and MHC‐II diversity and latitude. We also explored the relationship between infection status and latitude/biome. We found a non‐linear association between the MHC‐II amino acidic allele diversity and latitude. Individuals from north Chile presented a lower MHC genetic diversity than those from other locations. We also found an association between deserts and xeric shrublands and a lower prevalence of Haemoproteus parasites. Our results support a lower MHC genetic in arid or semi‐arid habitats in the region with the lower prevalence of Haemoproteus parasites.

The urban environment produces complex relationship among urban stressors that could change the levels of the steroid hormone, glucocorticoid (GCs). Studies that have evaluated baseline corticosterone (Cort) levels (the main GC in birds) and stress responses during development in urban and rural environments have obtained contrasting results. This ambiguity could partially be because the studies were carried out in altricial species, where parental care and sibling competition can affect Cort levels. Therefore, in this study, we compared levels of circulating baseline levels of CORT (blood sample obtained within 3 min of capture) and stress responses (blood sample obtained 30 min after capture) and the H/L ratio (an alternative method to measure stress) in chicks of a precocial bird, southern lapwings (Vanellus chilensis), from one rural (6 chicks), one urban low-polluted (13 chicks), and one urban high-polluted (10 chicks) site of Metropolitan Region of Santiago de Chile. We observed higher baseline Cort (2.41 ± 1.78 ng/mL) in the urban high-polluted site, a higher H/L ratio (0.51 ± 0.20) in the urban low-polluted site, and similar stress response across the three sites. We propose that the difference in stress physiology we observed within Santiago de Chile is because the two zones are at extremes in terms of stressors (noise, light, chemical, and human presence). It is unusual to find a precocious bird that lives in both urban and rural areas; therefore, the results of this study will advance our knowledge of the effect of the urban environment during the development of wildlife, which is relevant in terms of management and conservation.

Los virus de influenza aviar (VIA) son patógenos importantes en aves acuáticas silvestres a nivel mundial; sin embargo, su presencia en regiones subantárticas sigue siendo en gran medida desconocida. Para abordar esta brecha en el conocimiento, se presentan aquí datos de vigilancia obtenidos en la Reserva de la Biosfera Cabo de Hornos, en el extremo sur de Chile, durante las temporadas reproductivas australes de 2024-2025. En total, se recolectaron 352 muestras fecales de sitios costeros, islotes y aves paserinas en programas de monitoreo a largo plazo. Solo una muestra ambiental obtenida en Punta Gusano en enero de 2024 resultó positiva mediante RT-PCR en tiempo real (Ct 36,78), lo que corresponde a una tasa de detección del 0,625%, mientras que todas las muestras de paserinos y de la temporada 2025 fueron negativas. Este único resultado débilmente positivo sugiere introducciones virales ocasionales, pero no hay evidencia de circulación sostenida. El hallazgo coincide con informes previos que muestran una dinámica activa de VIA en el norte y centro de Chile, pero una actividad muy limitada en la Patagonia. Asimismo, concuerda con los pocos casos confirmados de influenza aviar altamente patogénica H5N1 del clado 2.3.4.4b registrados en el extremo sur de Chile durante el brote de 2023. En conjunto, estas observaciones sugieren que el extremo sur de Chile sigue estando mínimamente afectado por los VIA. No obstante, su proximidad a la Antártida y su ubicación en la intersección de importantes rutas migratorias resaltan la importancia de mantener la vigilancia en estos ecosistemas remotos.