Long-term demographic dynamics of a keystone scavenger disrupted by human-induced shifts in food availability

Age and sex differences in pharmaceutical contamination in a keystone scavenger

Pharmaceutical contaminants have a recognized negative impact on wildlife health. However, there are still many knowledge gaps on the factors influencing exposure and metabolic processing of compound mixtures as a function of season and individual characteristics such as age and sex. We evaluated age and sex differences in a set of seventeen compounds, including eleven antibiotics, five NSAIDs and caffeine, evaluated by HPLC-MS-TOF analysis in griffon vultures (Gyps fulvus) from central Spain. Pharmaceutical cocktails (up to 10 compounds simultaneously) were found in all individuals. Lincomycin was detected in all individuals, and fluoroquinolones were found at high frequencies, while NSAIDs were at low frequencies and concentrations, including flumixin meglumine, which can be lethal to vultures. A higher total number of compounds and sum of concentrations, as well as prevalence and concentration of several of the pharmaceuticals tested was found in females than in males for both nestlings and adults. This is the first study to present evidence of sex differences in the pharmacokinetics of dietary drug contaminants in a vulture species. Chronic exposure to "medications" in entire populations can potentially have sub-lethal health effects that affect fitness differently according to age and sex, with demographic implications for population viability. Specifically, if females have higher mortality after fledging due to high pharmaceutical contamination, this should be considered when modelling the population dynamic of this species for conservation purposes.

Interspecific differences in plasma carotenoid profiles in nestlings of three sympatric vulture species

Carotenoids are diet-based micronutrients important in health and coloration signaling. Related species with similar diets can differ in the kinds and levels of circulating carotenoids, which suggests specific physiological mechanisms to efficiently utilize these micronutrients, regardless of their availability. We explored whether diet and parental provisioning of unusual sources of carotenoids (fresh vegetal matter and vertebrate feces) can explain the occurrence and concentrations of carotenoids in the cinereous vulture Aegypius monachus, griffon vulture Gyps fulvus, and Egyptian vulture Neophron percnopterus nestlings, even when these pigments appear to not be deposited in their integumentary system. A greater diversity of wild prey in diet could be behind the profile of higher concentrations of carotenoids in the Egyptian vulture, the species with carotenoid-dependent coloration during adulthood, while differences in diet composition between cinereous and griffon vultures do not translate to different carotenoid profiles. The carotenoid profile appears to not be related to the ingestion of unusual matter rich in these compounds, although the infrequent occurrence of lycopene and unidentified γ-carotene-like compounds suggest that these vultures may be exploiting vegetal matter that left no identifiable unconsumed remains in the nest of Egyptian vultures. The consumption of green plant material by griffon vultures does not result in especially high levels of carotenoids when compared to the carotenoids found in cinereous vultures, which do not consume green plant material. Ungulate feces were not provisioned to Egyptian vulture nestlings, despite the fact they contain carotenoids that adults need for appropriate coloration. Overall, this study indicates that diet differences alone appear insufficient to explain contrasting interspecific carotenoid profiles, especially since all types of food consumed are considered to be poor in carotenoids, except vegetable matter. We suggest that nestling Egyptian vultures are comparatively efficient in uptaking carotenoids present in low concentrations in food when these compounds are not deposited in their integument, which suggests allocation to other functions.

Age-Specific Demographic Response of a Long-Lived Scavenger Species to Reduction of Organic Matter in a Landfill

Food availability shapes demographic parameters and population dynamics. Certain species have adapted to predictable anthropogenic food resources like landfills. However, abrupt shifts in food availability can negatively impact such populations. While changes in survival are expected, the age-related effects remain poorly understood, particularly in long-lived scavenger species. We investigated the age-specific demographic response of a Griffon vulture (Gyps fulvus) population to a reduction in organic matter in a landfill and analyzed apparent survival and the probability of transience after initial capture using a Bayesian Cormack-Jolly-Seber model on data from 2012-2022. The proportion of transients among newly captured immatures and adults increased after the reduction in food. Juvenile apparent survival declined, increased in immature residents, and decreased in adult residents. These results suggest that there was a greater likelihood of permanent emigration due to intensified intraspecific competition following the reduction in food. Interestingly, resident immatures showed the opposite trend, suggesting the persistence of high-quality individuals despite the food scarcity. Although the reasons behind the reduced apparent survival of resident adults in the final four years of the study remain unclear, non-natural mortality potentially plays a part. In Europe landfill closure regulations are being implemented and pose a threat to avian scavenger populations, which underlines the need for research on food scarcity scenarios and proper conservation measures.

Insularity determines nestling sex ratio variation in Egyptian vulture populations

Variation in offspring sex ratio, particularly in birds, has been frequently studied over the last century, although seldom using long-term monitoring data. In raptors, the cost of raising males and females is not equal, and several variables have been found to have significant effects on sex ratio, including food availability, parental age, and hatching order. Sex ratio differences between island populations and their mainland counterparts have been poorly documented, despite broad scientific literature on the island syndrome reporting substantial differences in population demography and ecology. Here, we assessed individual and environmental factors potentially affecting the secondary sex ratio of the long-lived Egyptian vulture Neophron percnopterus. We used data collected from Spanish mainland and island populations over a ca. 30-year period (1995-2021) to assess the effects of insularity, parental age, breeding phenology, brood size, hatching order, type of breeding unit (pairs vs. trios), and spatial and temporal variability on offspring sex ratio. No sex bias was found at the population level, but two opposite trends were observed between mainland and island populations consistent with the island syndrome. Offspring sex ratio was nonsignificantly female-biased in mainland Spain (0.47, n = 1112) but significantly male-biased in the Canary Islands (0.55, n = 499), where a male-biased mortality among immatures could be compensating for offspring biases and maintaining a paired adult sex ratio. Temporal and spatial variation in food availability might also have some influence on sex ratio, although the difficulties in quantifying them preclude us from determining the magnitude of such influence. This study shows that insularity influences the offspring sex ratio of the Egyptian vulture through several processes that can affect island and mainland populations differentially. Our research contributes to improving our understanding of sex allocation theory by investigating whether sex ratio deviations from parity are possible as a response to changing environments comprised by multiple and complexly interrelated factors.

Admission Causes, Morbidity, and Outcomes in Scavenger Birds in the North of Portugal (2005-2022)

Portugal is the habitat of three species of vultures. According to the IUCN Red List of Threatened Species, Neophron percnopterus is an Endangered species, Aegypius monachus is nearly Threatened, and Gyps fulvus is of Least Concern. This study aims to investigate the admission causes, morbidity, and outcomes of vultures admitted to a wildlife rehabilitation centre and necropsy service in Northern Portugal. Over 17 years (2005-2022), 84 animals were admitted: 10 A. monachus, 69 G. fulvus, and 5 N. percnopterus. The main causes of admission to the centre were 80% (n = 63) unknown cause, 13% (n = 10) found debilitated, 6 % (n = 5) vehicle collision, 4% (n = 3) captivity, 1% (n = 1) gunshot, and 1% (n = 1) electrocution. Most animals were admitted during the summer (45.2%) and autumn (36.9%). Analysis of outcome data showed that 73% (n = 58) of the animals that arrived alive at the centre could be rehabilitated and released back into the wild. Thirteen animals died during treatment and five were found dead. This is the first time that such a lengthy study of results and mortality has been carried out for these species in Portugal. Although the data are limited, they can already provide some information about these populations, particularly for the endangered species that are so rare to observe.

Nestling sex ratio is unaffected by individual and population traits in the griffon vulture

Variation in offspring sex ratios is a central topic in animal demography and population dynamics. Most studies have focused on bird species with marked sexual dimorphism and multiple-nestling broods, where the offspring sex ratio is often biased due to different individual or environmental variables. However, biases in offspring sex ratios have been far less investigated in monomorphic and single-egg laying species, and few studies have evaluated long-term and large-scale variations in the sex ratio of nestling vultures. Here, we explore individual and environmental factors potentially affecting the secondary sex ratio of the monomorphic griffon vulture Gyps fulvus. We used information collected at three breeding nuclei from central Spain over a 30-year period (1990-2020) to analyse the effects of nestling age, parental age, breeding phenology, conspecific density, population reproductive parameters, and spatial and temporal variability on nestling sex. Sex ratio did not differ from parity either at the population or the nuclei level. No significant between-year differences were detected, even under highly changing conditions of food availability associated with the mad-cow crisis. We found that tree nesting breeders tend to have more sons than daughters, but as this nesting behavior is rare and we consequently have a small sample size, this issue would require additional examination. Whereas further research is needed to assess the potential effect of breeder identity on nestling sex ratio, this study contributes to understanding the basic ecology and population dynamics of Griffon Vultures, a long-lived species with deferred maturity and low fecundity, whose minor deviations in the offspring sex ratio might imply major changes at the population level.

Insights on the best release strategy from post-release movements and mortality patterns in an avian scavenger

Conservation translocations involving vultures rely either on soft- or hard-release strategies. To investigate whether these strategies affect home range stability and survival, we compared the spatial behavior and mortality of 38 Griffon vultures (Gyps fulvus) released in Sardinia. Griffons were released after no acclimatization or after 3 (short) or 15 (long acclimatization) months in an aviary. In the two years that followed their release, griffons without acclimatization did not stabilize their home range size, while those subjected to long acclimatization stabilized it in the second year. Short-acclimatized griffons always had a large home range, soon after their release. The number of individuals that reached sexual maturity was higher (71.4%) in long-acclimatized griffons than in short-acclimatized ones (40%) or in griffons that were hard released (28.6%). Soft release with a long acclimatization period seems to be the most successful method to ensure stable home ranges and the survival of griffon vultures.

Large-scale movement patterns in a social vulture are influenced by seasonality, sex, and breeding region

Quantifying space use and segregation, as well as the extrinsic and intrinsic factors affecting them, is crucial to increase our knowledge of species-specific movement ecology and to design effective management and conservation measures. This is particularly relevant in the case of species that are highly mobile and dependent on sparse and unpredictable trophic resources, such as vultures. Here, we used the GPS-tagged data of 127 adult Griffon Vultures Gyps fulvus captured at five different breeding regions in Spain to describe the movement patterns (home-range size and fidelity, and monthly cumulative distance). We also examined how individual sex, season, and breeding region determined the cumulative distance traveled and the size and overlap between consecutive monthly home-ranges. Overall, Griffon Vultures exhibited very large annual home-range sizes of 5027 ± 2123 km2, mean monthly cumulative distances of 1776 ± 1497 km, and showed a monthly home-range fidelity of 67.8 ± 25.5%. However, individuals from northern breeding regions showed smaller home-ranges and traveled shorter monthly distances than those from southern ones. In all cases, home-ranges were larger in spring and summer than in winter and autumn, which could be related to difference in flying conditions and food requirements associated with reproduction. Moreover, females showed larger home-ranges and less monthly fidelity than males, indicating that the latter tended to use the similar areas throughout the year. Overall, our results indicate that both extrinsic and intrinsic factors modulate the home-range of the Griffon Vulture and that spatial segregation depends on sex and season at the individual level, without relevant differences between breeding regions in individual site fidelity. These results have important implications for conservation, such as identifying key threat factors necessary to improve management actions and policy decisions.