Assessing metabolite profiles of wild Swainson's thrushes (Catharus ustulatus) in different moult stages using a veterinary point of care device

Migration and moult are both energetically demanding and have conflicting physiological requirements, therefore usually separated in time. In some species, individuals may interrupt their migration to moult at discrete stopover locations outside of their breeding grounds (i.e., moult-migration) leading to competing physiological demands for moult and migration as protein is needed both for feather regeneration and efficient migration. Here, we examine the plasma metabolite profiles between moulting and post-moulting migrants by using a point-of-care analyzer providing real-time data in the field. Post-moulting birds, who were on shorter migration stopovers, had significantly higher concentrations of aspartate aminotransferase, calcium, sodium, phosphorous, and total protein than moulting birds, which is consistent with higher metabolic demands during migration and depletion of protein due to feather regeneration during moult. Additionally, uric acid, creatine kinase, total protein, aspartate aminotransferase, and potassium – all indicative of protein catabolism, muscle damage, and dehydration – were higher in lighter birds (below a scaled mass index of 7–7.5) regardless of moult status, which is consistent with lower energy reserves reflecting nutritional stress. Together, these metabolite profiles, measured in situ at a banding station, provide real-time insight into how birds mitigate the physiologically competing demands of moult and migration at a peri-urban stopover.