Data from: Comparative analysis of the plasma metabolome of migrating passerines: Novel insights into stopover metabolism

During long-distance migration, many birds experience periods of either
prolonged fasting (during endurance flights) or extensive feeding (during
stopovers). Despite decades of research on avian metabolism during
migration, many questions have remained unanswered, as such research
mainly focused on targeted metabolites and fat metabolism. Here, we
examined the plasma-metabolome of two migrating passerine species before
they crossed the Sahara Desert. Birds were sampled at two sites populated
by Pistacia trees bearing fat-rich fruits and at an additional site
dominated by blooming Eucalyptus trees. The blood samples were analyzed
using both GC-MS and LC-MS, using an untargeted approach. Examination of
metabolic pathways activated during stopovers indicated a crucial role for
cycling glucose through the Cori and Cahill cycles in resting and recovery
processes. This novel perspective, conducted on free-ranging birds,
suggests the evolution of avian insulin resistance due to factors such as
endurance exercise, fasting, and a preference for fatty acid oxidation
during migration, akin to cell trauma recovery. We detected significant
inter-site variations in birds' polar and lipophilic metabolic
profiles. We interpret the differences in the polar metabolites to be
associated with the physiological state of the birds, with birds that are
considered to have landed in the night prior to capture showing different
metabolic profiles compared to birds that have spent more time at the
stopover site. In contrast, distinctions in the lipophilic profiles of
birds were associated with variations in the primary food source that was
available to them in the different sites. This study underscores the
challenge of interpreting commonly used indicators for assessing migrating
birds' physiological state, which was predominantly derived from
lipid metabolism in complex ecological systems.