Francisco Santiago-Quesada

Long lengths of stay, large numbers, and trends of the Black-tailed Godwit Limosa limosa in rice fields during spring migration

Rice fields provide functional wetlands for declining shorebirds and other waterbirds around the world, but fundamental aspects of their stopover ecology in rice fields remain unknown. We estimated the length of stay of Black-tailed Godwits Limosa limosa migrating through rice fields, and showed the international importance of Extremadura’s rice fields (south-west Spain) for this Near Threatened shorebird species. Overall, large numbers of Black-tailed Godwits en route to their breeding grounds had long lengths of stay in the rice fields (34.7 ± 1.7, 14.4 ± 2.0 and 8.3 ± 1.2 days in godwits radio-tagged in late January, early February, and late February, respectively). The long lengths of stay of godwits in rice fields, together with some aspects of their feeding ecology, suggest that rice fields are suitable staging habitats, and therefore they could play an important role as buffer habitats against the loss or degradation of natural wetlands. Extremadura’s rice fields supported at least 14% of the declining Western European population of Black-tailed Godwit, and its increasing number in south-west Spain probably reflects a population shift towards the northern part of the winter range. We strongly suggest the inclusion of Extremadura’s rice fields as a Special Protection Area for birds under the European Union Directive on the conservation of wild birds.

Effects of Diet on Growth-Related Patterns of Energy and Macronutrient Assimilation Efficiency in a Semi-Precocial Bird, the Gull-Billed Tern Gelochelidon nilotica

Albano N., Masero J.A., Sánchez-Guzmán J.M., Villegas A. & Santiago-Quesada F. 2011. Effects of diet on growth-related patterns of energy and macronutrient assimilation efficiency in a semi-precocial bird, the Gull-billed Tern Gelochelidon nilotica. Ardea 99: 93–101. Despite the extensive literature on energy assimilation efficiency in birds, only a few studies have dealt specifically with offspring, and to our knowledge there is no information on macronutrient assimilation efficiencies during the growth period of chicks. We studied growth-related energy and macronutrient assimilation efficiencies of semi-precocial chicks of Gull-billed Terns Gelochelidon nilotica as a function of their diet. We experimentally evaluated several digestive parameters in chicks fed different diets — fish vs. insects — when 10, 15 and 22 days old. Gross daily energy intake was similar in the two groups throughout the growth period, but fish-fed chicks showed consistently higher energy and macronutrient assimilation efficiencies than chicks fed insects. Energy and macronutrient assimilation efficiencies varied with age, peaking at 15 days old. The only digestive parameter that did not decrease during the last phase of growth was the lipid assimilation efficiency. Fish-fed chicks grew significantly faster than those fed on insects, which showed delayed growth. We suggest that semi-precocial chicks could modulate energy and macronutrient assimilation efficiency according to their growth requirements and that such digestive parameters can help us to understand differences in chick growth rates and breeding success in a natural environment.

Plasma metabolites correlate with weekly body mass changes in migrating black-tailed Godwits Limosa limosa feeding on different diets

AbstractThe study of variations in plasma metabolite profiles has emerged as a useful physiological tool to assess fuel deposition rates from a single blood sample. Diet may be a key factor in the study of refueling patterns in long-distance migratory birds, but the potential confounding effect of diet on the conclusions drawn from plasma metabolites has rarely been considered. Here, we assessed whether plasma metabolite levels correlate with the weekly increase in body mass of migrating Black-tailed Godwits Limosa limosa, a medium–large shorebird, feeding on two natural diets (insectivorous vs. granivorous) during the refueling period. We found that glycerol and triglycerides successfully explained the weekly natural change in body mass of Black-tailed Godwits. Although the diet type contributed to the change in body mass, all interactions between plasma metabolites and diet treatment were non-significant. Our results support the use of plasma metabolite profiling to predict body mass changes on a long-term (weekly) scale in medium–large birds.ZusammenfassungPlasma-Metaboliten korrelieren mit wöchentlichen Körpermasse-Änderungen bei ziehenden Uferschnepfen (Limosa limosa) mit unterschiedlicher Ernährung Die Untersuchung von Unterschieden in den Profilen von Plasma-Metaboliten ist inzwischen ein nützliches physiologisches Werkzeug, um die Füllung der Energiespeicher aus einer einzigen Blutprobe abzuschätzen. Ernährung könnte ein Schlüsselfaktor sein in der Untersuchung von Mustern der Zwischenstopps für die Nahrungsaufnahme bei Langstreckenziehern, aber die möglichen Effekte der Ernährung auf die Schlussfolgerungen, die aus der Messung der Plasma-Metaboliten gezogen werden, wurde selten in Erwägung gezogen. Hier untersuchen wir, ob Plasma-Metabolitlevel mit der wöchentlichen Gewichtszunahme ziehender Uferschnepfen korrelieren, einer mittelgroßen Limikolenart, die sich auf Zwischenstopps entweder von Insekten oder von Körnern und Samen ernähren. Wir fanden, dass Plasma-Glycerin und Plasma-Triglyceride die natürliche wöchentliche Änderung im Körpergewicht von Uferschnepfen erfolgreich erklärten. Die Ernährungsweise hatte einen Einfluss auf die Änderung der Körpermasse bei Uferschnepfen, aber alle Interaktionen zwischen Plasma-Metaboliten und Ernährung waren nicht signifikant. Unsere Ergebnisse unterstützen den Einsatz des Plasma-Metabolit Profiling, um Änderungen des Körpergewichts bei mittelgroßen Vögeln in einem längeren Zeitraum (Woche) vorauszusagen.

Wetland salinity induces sex-dependent carry-over effects on the individual performance of a long-distance migrant

Salinization is having a major impact on wetlands and its biota worldwide. Specifically, many migratory animals that rely on wetlands are increasingly exposed to elevated salinity on their nonbreeding grounds. Experimental evidence suggests that physiological challenges associated with increasing salinity may disrupt self-maintenance processes in these species. Nonetheless, the potential role of salinity as a driver of ecological carry-over effects remains unstudied. Here, we investigated the extent to which the use of saline wetlands during winter – inferred from feather stable isotope values – induces residual effects that carry over and influence physiological traits relevant to fitness in black-tailed godwits Limosa limosa limosa on their northward migration. Overwintering males and females were segregated by wetland salinity in West Africa, with females mostly occupying freshwater wetlands. The use of these wetlands along a gradient of salinities was associated with differences in immune responsiveness to phytohaemagglutinin and sized-corrected body mass in godwits staging in southern Europe during northward migration – 3,000 km from the nonbreeding grounds – but in males only. These findings provide a window onto the processes by which wetland salinity can induce carry-over effects and can help predict how migratory species should respond to future climate-induced increases in salinity.