Aplicaciones del estudio de la ultraestructura y composición de la cáscara de los huevos de quebrantahuesos ("Gypaetus barbatus") en la conservación de la especie

Abstract

The Bearded vulture (Gypaetus barbatus) is a long-lives threatened species with a European population of only 170 territories. The Spanish population, with 121 territories, is the largest European core, and conservation measures are being applied since 1985. However, in recent years, the population has been suffering from low rates of productivity and reproductive success which, in turn, are affecting the population dynamics and threatening its long-term viability. We evaluated the suitability of the study of eggshell using scanning electron microscopy in determining causes of breeding failure; eight samples from eggs collected prior to the massive use of pesticides were obtained from museums and allow us to characterize the normal ultrastructure of the Bearded vulture eggshell. The Bearded vulture eggshell is trilaminar and reticulate, with the calcified portion composed of three layers, as already described in other Falconiformes, and single pore channels and lacking the outer crystaline layer. All eggshell parameters showed higher range of variation than expected, suggesting that the Bearded vulture has a high capability for adaptation of different environmental conditions. From 1996 to 2013, in collaboration with the environmental authorities, 27 whole eggs and 90 eggshell fragments collected after breeding failure in nest of the Pyrenean population were studied. Levels of organochlorine pesticides and PCBs in whole eggs were also investigated. Toxicological analysis revealed low levels of contamination and, thus, that contamination with organochlorine pesticides was not the cause of breeding failure. Egg fertility was higher than expected in the studied sample and breeding failure was found to be mainly produced at the end of incubation or in the first days of the chick live. Fertile eggs were found to be longer, with thicker eggshells and higher Ratcliffe Index, thus showing better quality. From 2006 onwards, eggshell thickness and other eggshell parameters were decreasing. This lost of egg quality since 2006 was related to sanitary policies in the UE that caused sudden decrease in livestock carcasses and food shortages. Temporal changes in organochlorine levels also showed an increase since 2006, suggesting that the Bearded vultures are modifying their feeding and foraging strategies to exploit other food resources of lower quality and more contaminated, increasing the risk of consuming contaminated or poisoned preys.