Assessing the applicability of stable isotope analysis to determine the contribution of landfills to vultures' diet - PubMed (original) (raw)

Assessing the applicability of stable isotope analysis to determine the contribution of landfills to vultures' diet

Helena Tauler-Ametller et al. PLoS One. 2018.

Abstract

Human activities cause changes to occur in the environment that affect resource availability for wildlife. The increase in the human population of cities has led to a rise in the amount of waste deposited in landfills, installations that have become a new food resource for both pest and threatened species such as vultures. In this study we used stable isotope analysis (SIA) and conventional identification of food remains from Egyptian Vultures (Neophron percnopterus) to assess the applicability of SIA as a new tool for determining the composition of the diets of vultures, a group of avian scavengers that is threatened worldwide. We focused on an expanding Egyptian Vulture population in NE Iberian Peninsula to determine the part played by landfills and livestock in the diet of these species, and aimed to reduce the biases associated with conventional ways of identifying food remains. We compared proportions of diet composition obtained with isotope mixing models and conventional analysis for five main prey. The greatest agreement between the two methods was in the categories 'landfills' and 'birds' and the greatest differences between the results from the two methods were in the categories 'livestock', 'carnivores' and 'wild herbivores'. Despite uncertainty associated to SIA, our results showed that stable isotope analysis can help to distinguish between animals that rely on waste and so present enriched levels of δ 13C than those that feed on the countryside. Indeed, a high proportion of food derived from landfills (nearly 50%) was detected in some breeding pairs. Furthermore we performed GLMM analyses that showed that high values of δ 13C in Egyptian Vulture feathers (a proxy of feeding in landfills) are related with high levels of humanization of territories. This method has the potential to be applied to other threatened vulture species for which there is a lack of information regarding resources they are consuming, being especially important as the main causes of vultures decline worldwide are related to the consumption and availability of food resources.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Distribution of breeding pairs (yellow circles) and landfills (green symbols) located inside our study area and considered for diet analysis.

Grey gradient represent altitudes from 0 m (white) to 3000 m (black). Two important cities are also represented.

Fig 2. Proportion of diet of Egyptian Vulture represented by main prey categories obtained by stable isotope analysis and conventional identification of food remains.

Medians, quartiles and outliers of each prey category are represented in the boxplot.

Fig 3. Isotopic values (δ 13C and δ 15N) of Egyptian Vulture nestlings in Catalonia (n = 60) and main sources of food (mean ± SD).

Same symbols correspond to the isotopic values of nestlings from the same territory but different years.

Fig 4. Percentage of the contribution of landfills in the diet of Egyptian Vulture nestlings estimated with Bayesian mixing models (SIMMR).

Data of each territorial pair but different year is represented with the same number. Boxes represent the credible interval of 50% and error bars the credible interval of 95% obtained with SIMMR.

Fig 5. Results of comparison of conventional methods and isotope analysis for the diet of Egyptian Vulture in Catalonia during the period 2012–2014.

(a) Probability of difference below 0 between stable isotope analysis and conventional analysis for main prey of Egyptian Vulture. (b) Mean differences between stable isotope analysis and conventional methods in estimates of the main prey of Egyptian Vulture. Standard errors of the differences are represented.

References

1. Foley JA, DeFries R, Asner GP, Barford C, Bonan G, Carpenter SR, et al. Global Consequences of Land Use. Science (80-). 2005;309: 570–574. doi: 10.1126/science.1111772 -DOI -PubMed
1. Donazar JA, Negro JJ, Hiraldo F, Hiraldo F. Foraging habitat selection, land-use changes and population decline in the lesser kestrel Falco naumanni. J Appl Ecol. 1993;30: 515–522. doi: 10.2307/2404191 -DOI
1. Blanco G, Tella JL, Torre I. for habitats and key foraging farming Traditional in a conservation pyrrhocorax chough Pyrrhocorax landscape Spanish pseudosteppe. J Appl Ecol. 1998;35: 232–239.
1. Laiolo P, Dondero F, Ciliento E, Rolando A. Consequences of Pastoral Abandonment for the Structure and Diversity of the Alpine Avifauna Published by: British Ecological Society Consequences of pastoral abandonment for the structure and diversity of the alpine avifauna. J Appl Ecol. 2004;41: 294–304.
1. Oro D, Genovart M, Tavecchia G, Fowler MS, Martínez-Abraín A. Ecological and evolutionary implications of food subsidies from humans. Ecol Lett. 2013;16: 1501–1514. doi: 10.1111/ele.12187 -DOI -PubMed

Assessing the applicability of stable isotope analysis to determine the contribution of landfills to vultures' diet - PubMed (original) (raw)