Heterophile/Lymphocyte Profiles are Associated with Mass Increase and Moulting in the Semipalmated Sandpiper Calidris pusilla at Wintering Sites in NE South America

Abstract. Leukocyte profiles, such as the heterophile/lymphocyte (H/L) ratio, are influenced by several ecological and ecophysiological factors and are generally considered to be independent and robust indicators of stress levels in birds. We tested the hypotheses that Semipalmated Sandpiper Calidris pusilla presents a positive association between physiological stress (H/L ratio) and molt, and that there should be a negative association between physiological stress (H/L ratio) and body condition (mass). During its annual cycle, Semipalmated Sandpiper performs long-distance migrations and often arrives in South America in September/October when it can undergo molting before its migration to the north. In May, while preparing to return to its reproductive sites, Semipalmated Sandpiper increases its body mass. The research was carried out on Restinga Island of the Rio Paraíba estuary in northeast Brazil. Data collection took place during the wintering of Semipalmated Sandpiper in October 2017 and February and May 2018. We found a positive association between the H/L ratio and the presence of molt in October and February, but a negative association between the H/L ratio and body mass in May. Our results support the hypotheses that the presence of molt should be positively associated with the H/L ratio due to the high energy and nutritional costs that molting requires and that the H/L ratio and body mass should be negatively associated due to the favorable nutritional status of Semipalmated Sandpiper during its preparation to migrate to its reproductive areas.