Linking migratory performance to breeding phenology and productivity in an Afro-Palearctic long-distance migrant

Radar-measured passerine vertical speeds reveal a migratory switch near a major barrier

Successful accomplishment of long-distance migration necessitates optimal decision-making processes. Throughout their migration, birds need to constantly choose to fly or to stop. Passerine migrants integrate internal (e.g., lipid deposition) and external (e.g., prevailing winds) factors resulting in specific departure or landing times. We calculated individual departure and landing timing using vertical-looking radar in the Hula Valley, compiled nightly departure and landing ratios (departure and landing amounts relative to total migration flux), and explored how these are affected by meteorological conditions. Crosswind direction emerged as a key factor affecting departure and landing decisions during autumn migration in the area. Birds avoided drifting toward the Mediterranean Sea by landing and preferred taking off when winds blew away from the sea. Our findings represent an undescribed migration initiation and termination switch with implications for flight and stopover scheduling. The method extends the scope of aeroecological research for addressing individual-level migration behavior.

Molecular Changes in the Brain of the Wintering Calidris pusilla in the Mangroves of the Amazon River Estuary

Migrant birds prepare differently to fly north for breeding in the spring and for the flight to lower latitudes during autumn, avoiding the cold and food shortages of the Northern Hemisphere's harsh winter. The molecular events associated with these fundamental stages in the life history of migrants include the differential gene expression in different tissues. Semipalmated sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that migrate to the coast of South America during the non-breeding season. In a previous study, we demonstrated that between the beginning and the end of the wintering period, substantial glial changes and neurogenesis occur in the brain of C. pusilla. These changes follow the epic journey of the autumn migration when a 5-day non-stop transatlantic flight towards the coast of South America and the subsequent preparation for the long-distance flight of the spring migration takes place. Here, we tested the hypothesis that the differential gene expressions observed in the brains of individuals captured in the autumn and spring windows are consistent with the previously described cellular changes. We searched for differential gene expressions in the brain of the semipalmated sandpiper, of recently arrived birds (RA) from the autumnal migration, and that of individuals in the premigratory period (PM) in the spring. All individuals were collected in the tropical coastal of northern Brazil in the mangrove region of the Amazon River estuary. We generated a de novo neurotranscriptome for C. pusilla individuals and compared the gene expressions across libraries. To that end, we mapped an RNA-Seq that reads to the C. pusilla neurotranscriptome in four brain samples of each group and found that the differential gene expressions in newly arrived and premigratory birds were related with neurogenesis, metabolic pathways (ketone body biosynthetic and the catabolic and lipid biosynthetic processes), and glial changes (astrocyte-dopaminergic neuron signaling, astrocyte differentiation, astrocyte cell migration, and astrocyte activation involved in immune response), as well as genes related to the immune response to virus infections (Type I Interferons), inflammatory cytokines (IL-6, IL-1β, TNF, and NF-κB), NLRP3 inflammasome, anti-inflammatory cytokines (IL-10), and cell death pathways (pyroptosis- and caspase-related changes).