Auxiliadora Villegas

Blood chemistry and haematocrit of the black vulture (Aegypius monachus)

We determined the values of haematocrit and blood chemistry of the black vulture (Aegypius monachus) in Extremadura (Spain). We analysed 57 nestlings, five feral adults, seven captive individuals in their first year and five captive adults. Free-living adults had a higher haematocrit and lower calcium and alkaline phosphatases concentrations than captive birds. There were differences in haematocrit and in the concentrations of glucose, uric acid, total proteins, alkaline phosphatases, phosphorus and aspartate aminotransferase between nestlings and young in their first year and adults. The estimated age of the nestlings was significantly correlated with haematocrit, plasma glucose and total protein concentrations. The physical condition of nestlings was significantly correlated with plasma alkaline phosphatases levels.

Understanding the energetic costs of living in saline environments: effects of salinity on basal metabolic rate, body mass and daily energy consumption of a long-distance migratory shorebird

SUMMARY Many migratory vertebrates typically move between habitats with varying salinities during the annual cycle. These organisms clearly exhibit a remarkable phenotypic flexibility in their ‘osmoregulatory machinery’, but the metabolic consequences of salinity acclimatization are still not well understood. We investigated the effects of salinity on basal metabolic rate (BMR), body mass and daily energy consumption of a long-distance migratory shorebird, the dunlin (Calidris alpina), outside the breeding season. Mass-corrected BMR and daily energy consumption increased significantly by 17 and 20% between freshwater (0.3‰ NaCl) and saltwater (33.0–35.0‰ NaCl), respectively. Body mass in both captive and wild dunlins was lower (9–16%) in saline than in freshwater environments. These changes on BMR and body mass were quickly reversed by returning the birds to freshwater, suggesting that metabolic adjustment to saltwater and metabolic readjustment to freshwater are both processes that occur in a few days. Our findings support empirically that the processes of developing and maintaining an active osmoregulatory machinery are energetically expensive, and they could help to explain diet and/or habitat selection patterns along the flyway. Finally, we discuss whether body mass loss in saltwater may be a strategy to reduce maintenance cost in osmotically stressful conditions such as overwintering in marine habitats, and raise some methodological implications for studies of BMR-related outcomes using captive birds captured in saline environments.

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.

Immune response to an endotoxin challenge involves multiple immune parameters and is consistent among the annual-cycle stages of a free-living temperate zone bird

SUMMARY Trade-offs between immune function and other physiological and behavioural processes are central in ecoimmunology, but one important problem is how to distinguish a reallocation of resources away from the immune system from a reallocation or redistribution within the immune system. While variation in baseline values of individual immune parameters is well established, studies in wild animals on multiple parameters during an immune response are lacking. It also remains to be tested whether and how immune responses correlate with baseline values that vary, for example, over the course of an annual cycle. We studied immunological responses to an endotoxin challenge in skylarks (Alauda arvensis), a partial migrant bird breeding in temperate zones. We compared birds injected with the endotoxin LPS with un-injected controls, characterizing immunological responses with leukocyte profiles, titres of lytic enzymes and natural antibodies, and concentrations of haptoglobin and heat shock proteins. We did this in five annual-cycle stages to test whether the response varied throughout the year. The endotoxin challenge affected six of 10 measured parameters. Lysis titres and proportions of heterophils increased; haptoglobin concentrations and proportions of lymphocytes, basophils and eosinophils decreased. The variable effects on different immune components demonstrate the complexity of an immune response. We found no evidence that the response differed between annual-cycle stages. The response was independent of baseline measures taken directly upon capture in the field, indicating that birds were facing no immunological ceiling when mounting an immune response. Values of five parameters collected under field conditions were significantly related to values taken under standardized laboratory conditions. We conclude that multiple parts of the immune system are modulated during an immunological response and that responses are not re-organized throughout the annual cycle.

Blood values of Bald Ibis (Geronticus eremita) in captivity: comparative ranges and variability with age, sex and physical condition

The Bald Ibis (Geronticus eremita) is one of the world’s most threatened species of birds. The number of individuals in captivity is several times greater than the number of individuals in the wild, so that the re-introduction of individuals from captive breeding into their natural habitat may be vital for the recovery of the species. A knowledge of the health problems associated with the handling of captive individuals and the improvement of their veterinary care could have great importance in determining the success of these captive breeding programs. Haematology and blood chemistry are very useful complementary tools in the diagnosis and treatment of diseases in birds, and provide valuable information about the individual’s nutritional status and physical condition. The present work reports haematocrit and blood chemistry values for individuals belonging to a captive population of this species, and analyses their variability with respect to age, sex, and physical condition of the animals. Adults presented greater values of haematocrit, uric acid, total proteins, cholesterol, and aspartate amine transferase than the young. With respect to sex differences, adult female birds had higher concentrations of alkaline phosphatase than males, contrary to previous results for captive individuals of this species. The condition index of adults was positively correlated with triglycerides, glucose, and alkaline phosphatase levels, and negatively with urea and lactate dehydrogenase levels. These results may be very useful as a complementary diagnosis tool during the veterinary care of individuals of this species included in re-introduction programs.

International importance of Extremadura, Spain, for overwintering migratory dabbling ducks: a role for reservoirs.

Many migratory waterbird populations are in decline and loss of natural wetlands is one of the main causes.However, some speciesmay respondpositively to artificial wetland recreation. In Extremadura (south-west Europe), several large reservoirs were created for irrigation since the 1960s and some comparatively small reservoirs were built from the late 1990s onwards close to rice fields. Here we analyse the abundance of wintering dabbling ducks (Anas spp.) in Extremadura before (1991–1994) and after (2007–2010) the creation of these new reservoirs in order to address the current importance of the area for this guild within the East Atlantic Flyway (EAF). A mean of 25,277 dabbling ducks wintered in the study area during 1991–1994, increasing to 46,163 individuals during 2007–2010. After controlling for environmental variables, Northern Pintail Anas acuta, Common Teal A. crecca and Northern Shoveler A. clypeata experienced significant increases in the area between both periods, and only Eurasian Wigeon A. penelope suffered a significant decrease. Mallard A. platyrhynchos and Gadwall A. strepera populations did not show any significant trend. The large older reservoirs experienced overall population decreases between the two periods, with four new reservoirs holding more than 35,000 wintering dabbling ducks. Our results reflect an overall improvement in habitat conditions, driven by the creation of reservoirs near to rice fields that could have resulted in a partial redistribution of wintering dabbling ducks in the EAF. The area emerges as one of the most important wintering sites for dabbling ducks in southern Europe, regularly exceeding two of the Ramsar Convention criteria for the conservation of several populations. The protection of these new reservoirs by legal mechanisms would guarantee the existence of a large functional wetland area, which could also mitigate the loss of natural wetlands for populations using the EAF.

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.

Diet Plasticity of Cinereous Vulture Aegypius monachus in Different Colonies in the Extremadura (SW Spain)

The current feeding habits of the Cinereous Vulture Aegypius monachus remain largely unknown since most studies were carried out in the 1970s. To update the information, we studied the diet of the species in different colonies in Extremadura by analyzing the frequency of presence of 378 prey items observed in 283 pellets. In all colonies, sheep carcasses formed the staple food. Nevertheless, there were major differences between colonies in supplementary prey: farm poultry and swine in Sierra de Gata, swine and deer in Sierra de San Pedro and Granadilla. There were also variations between subcolonies within a colony and differences with colonies elsewhere in the Iberian Peninsula. In colonies situated in areas with a high abundance of lagomorphs and deer, such as Cabañeros and Sierra de Andujar, the diet is based on wild animal populations. In other colonies, the diet depends to a large extent on livestock farming: sheep in Sierra de Gata, Granadilla and Sierra de San Pedro, and swine and sheep in Sierra de Guadarrama. The Cinereous Vulture thus shows great trophic plasticity, taking advantage of new resources (such as carcasses of poultry from poultry farms) and responding to variations in prey availability in the area surrounding the colonies. These circumstances need to be taken into consideration for the conservation of the species, in particular when the vultures depend on human resources, which are prone to drastic changes in availability. The recent outbreaks of veterinary diseases (like BSE, foot-and-mouth disease, Rift Valley fever and bluetongue disease) and reforms related to the Common Agricultural Policy, are a point in case.

Time Course and Metabolic Costs of a Humoral Immune Response in the Little Ringed Plover Charadrius dubius

Despite host defense against parasites and pathogens being considered a costly life-history trait, relatively few studies have assessed the energetic cost of immune responsiveness. Knowledge of such energetic costs may help to understand the mechanisms by which trade-offs with other demanding activities occur. The time course and associated metabolic costs of mounting a primary and secondary humoral immune response was examined in little ringed plovers Charadrius dubius challenged with sheep red blood cells. As was expected, the injection with this antigen increased the production of specific antibodies significantly, with peaks 6 d postinjection in both primary and secondary responses. At the peak of secondary antibody response, the antibody production was 29% higher than that observed during the primary response, but the difference was nonsignificant. Mounting the primary response did not significantly increase the resting metabolic rate (RMR) of birds, whereas the secondary response did by 21%, suggesting that the latter was more costly in terms of RMR. In spite of the fact that the primary response did not involve an increase in RMR, birds significantly decreased their body mass. This could imply an internal energy reallocation strategy to cope with the induced immune challenge. Last, we found that RMR and antibody production peaks were not coupled, which could help to conciliate the variable results of previous studies. Collectively, the results of this study support the hypothesis that humoral immunity, especially the secondary response, entails energetic costs that may trade-off with other physiological activities.

Sex-specific vulnerability to breeding conditions in chicks of the sexually monomorphic Gull-billed Tern

AbstractEnvironmental conditions during early development may differentially affect male and female offspring, and the effects of this sex–environment interaction in chick performance may be exaggerated under harsh conditions. In birds, most of the currently available evidence on sex-biased environmental sensitivity in nestlings is derived from species that display sexual size dimorphism, while studies on monomorphic or slightly dimorphic species are less abundant and have produced inconsistent results. We have evaluated sex-specific vulnerability to breeding conditions in chicks of the Gull-billed Tern (Gelochelidon nilotica), a semiprecocial species with only low sexual size dimorphism. We compared male and female mass growth and fledgling physiological condition (measured through plasma metabolite levels) in several colonies that differed in reproductive parameters. Chicks of both sexes grew more slowly and fledged with lower mass and poorer nutritional state in the colony with the worst breeding conditions, i.e., with later phenology and lower clutch size and reproductive success. Contrary to our expectations, chick vulnerability to rearing conditions was more pronounced for female than male fledglings. While males grew faster than females during the middle phase of growth regardless of colony, this difference disappeared later in the fledging period in all but the worst colony, where females maintained a lower mass and worse nutritional condition than males. These results add to the evidence that, even in monomorphic species, the environmental sensitivity of nestlings during development may vary in a sex-specific way that may select for sex-biased allocation of parental resources and sex ratio adjustments under specific breeding conditions.ZusammenfassungGeschlechtsspezifische Anfälligkeit gegen Aufzuchtsbedingungen bei Küken eines sexuell monomorphen Vogels, der Lachseeschwalbe Die Umweltbedingungen während der frühen Entwicklung können männliche und weibliche Nachkommen unterschiedlich beeinflussen, und diese Geschlechts-Umwelt-Interaktion in der Kükenperformanz kann unter harschen Bedingungen verstärkt sein. Bei Vögeln stammen die meisten Belege für geschlechtsspezifische Umweltempfindlichkeit aus Arten mit sexuellem Größendimorphismus, während Untersuchungen an monomorphen oder nur leicht dimorphen Arten seltener sind und widersprüchliche Ergebnisse erbracht haben. Hier schätzen wir die geschlechtsspezifische Anfälligkeit gegen die Aufzuchtsbedingungen bei Küken der Lachseeschwalbe (Gelochelidon nilotica) ab, einer halb-nestflüchtenden Art mit nur geringem sexuellen Größendimorphismus. Wir haben den Körpermassezuwachs von Männchen und Weibchen und ihre physiologische Kondition als Flügglinge (gemessen über den Plasmametabolitspiegel) in mehreren Kolonien, die sich in Fortpflanzungsparametern unterschieden, verglichen. Küken beiden Geschlechts wuchsen langsamer und wiesen beim Ausfliegen eine geringere Körpermasse und einen schlechteren Ernährungszustand auf in der Kolonie mit den schlechtesten Brutbedingungen, d.h. mit späterer Phänologie, kleinerer Gelegegröße und niedrigerem Fortpflanzungserfolg. Entgegen unserer Erwartungen waren weibliche Küken empfindlicher gegen die Aufzuchtsbedingungen als männliche. Während Männchen in der mittleren Wachstumsphase schneller wuchsen als Weibchen, unabhängig von der Kolonie, verschwand dieser Unterschied später in der Ausflugsperiode in allen Kolonien außer der schlechtesten, wo Weibchen weiterhin eine geringere Körpermasse und einen schlechteren Ernährungszustand als Männchen aufwiesen. Diese Ergebnisse liefern weitere Belege, dass selbst bei monomorphen Arten die Umweltempfindlichkeit der Nestlinge während der Entwicklung geschlechtsspezifisch variieren kann, was unter bestimmten Brutbedingungen eine verstärkte Zuteilung elterlicher Ressourcen zu einem Geschlecht sowie eine Anpassung des Geschlechterverhältnisses der Nachkommen begünstigen kann.