Casimiro Corbacho

Patterns of structural complexity and human disturbance of riparian vegetation in agricultural landscapes of a Mediterranean area

Abstract Riparian corridors are valuable high diversity habitats in Mediterranean-type environments and mainly in agricultural landscapes. Following a ‘vegetation complexes’ approach along fluvial landscapes, the factors affecting structural complexity and human disturbance through agricultural areas in south-west (SW) Spain were analysed. Using principal component analysis and a stepwise multiple regression analysis three main results were obtained: (1) a successional vegetative gradient was noted from upper (pioneer herbaceous communities) to lower reaches of streams (closed-canopy forests) with a concomitant increase in both woody cover and habitat diversity; (2) land-use intensity associated with each of the agricultural production methods, which was mainly related to topographic irregularity, appeared to be the main cause of human disturbance in riparian areas. Thus, the closed-canopy forests located in flat landscapes of lower streams were removed, highly modified or extensively fragmented; in contrast, riparian complexes placed on wild and rough landscapes of upper streams appeared as undisturbed or near-natural; (3) nearly 50% of the natural riparian vegetation of the study area has been highly modified or has disappeared, in most cases replaced by non-natural formations which have today become dominant. The protection of the few existing well-preserved riparian corridors and the restoration of highly altered riparian areas in the lower reaches of streams has become a priority in maintaining biodiversity in these agricultural Mediterranean landscapes. The extensive and cost-effective method developed for this study would be easily applicable to other large areas to evaluate the effect of human disturbance on riparian corridors.

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.

Identifying new buffer areas for conserving waterbirds in the Mediterranean basin: the importance of the rice fields in Extremadura, Spain

The impact of wetland loss on migratory waterbirds can be mitigated by the presence of anthropogenic habitats such as rice fields. In the Mediterranean basin, wetlands have been drained and altered to such a degree that their very existence is threatened. It is, therefore, essential to identify key buffer areas in the basin to develop conservation strategies for migratory waterbirds. In Extremadura, continental SW Spain, 30,000xa0ha of new rice fields have created since the 1960s. The present study describes for the first time the waterbird community associated with these inland rice fields, and addresses the question of the potential value of this area in buffering the loss of natural wetlands for populations of waterbirds using the East Atlantic Flyway (EAF). The waterbird community studied consisted of 45 species, with population levels reaching values of international importance (>1% of the biogeographical population using EAF) for the Common Crane Grus grus (19%), Black-tailed Godwit Limosa limosa (1.2%), Black-winged Stilt Himantopus himantopus (1.2%), and Cattle Egret Bubulcus ibis (1%). The presence of these rice fields may be modifying the wintering and/or feeding sites of some waterbird species such as the Common Crane and Black-tailed Godwit. Unfortunately, there is no legal protection for this area. We propose the designation of these rice fields as a Special Protection Area for birds.

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.

Colony-site Tenacity and Egg Color Crypsis in the Gull-billed Tern

Abstract Colony-site tenacity commonly reflects the stability of nesting habitats. The match between nesting substrate and coloration pattern of the eggs in two reproductive groups of the Gull-billed Tern (Gelochelidon nilotica) in the south of Iberian Peninsula was investigated to tests the adaptiveness of colony-site tenacity. The terns showing high colony-site tenacity had 1) a closer match in color between the eggs and the nesting substrate and 2) a lower richness and diversity of egg colors and 3) a lower rate of egg loss from predation than the low colony-site tenacity ones. These results appear to be adaptive, resulting from a long-standing renesting in the same colony-site. However, such mimicry would be difficult to achieve for terns with low site-tenacity, where breeding occur in unstable habitats. These birds were frequently obliged to move from one location to another due to weather irregularity and water level in the reservoirs they bred. In addition, the occasional high predation pressures on both adults and chicks, manifested by the low-tenacity tern group studied, was also involved. The attainment of such egg-crypsis could be an important adaptive advantage favoring colony-site tenacity. In unstable habitats, however, there would be a trade-off between the benefits linked to colony-site tenacity and the negative effects of suboptimal reproduction. Additional experimental design and studies are, however, necessary to confirm these results and predictions.

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.

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.

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 Lachseeschwalben 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.

Status and trends of Gull-billed Tern Gelochelidon nilotica in Europe and Africa

Summary Gull-billed Tern Gelochelidon nilotica is classed as Endangered in Europe (Tucker and Heath 1994, Hagemeijer and Blair, 1997), but there have been no detailed studies of the trends in the different populations occurring in Europe and Africa. Here we study the status and trends of the species in Europe and north and north-east Africa. We estimate the total population at 10,500–12,900 breeding pairs, and recognize two biogeographical populations in this region. The western population, comprising colonies in northern Europe (Denmark, Netherlands, Germany), France, Italy, Spain, and north and north-east Africa, consists of at most 6,200 pairs, 1,800 of which are in African colonies. The eastern population, comprising colonies in the Balkan Peninsula, Greece, shores of the Black Sea and Sea of Azov, and Turkey, consists of at most 6,800 pairs. Two trends were observed: a first phase from 1900 up to the mid-1970s in which the northern European populations practically disappeared; and a second phase of stabilization, or even increase, in some of the western colonies, while the eastern population continued to decline. There is a marked concentration of the species in just a few localities in the countries of the Mediterranean basin.