Effects of exposure to toxic elements on nightjars in areas contaminated by mining

    Exposure to toxic elements, the response of certain physiological parameters and their relationship with physical condition show that contamination could be a threat to nightjar populations in mining areas.


    The nighthawk (Order Caprimulgiformes), also called deceive shepherds, are a group of insectivorous birds that owe their peculiar name to the false popular belief that they went out at night to "suck" the goats' milk. Far from the old superstitions, the truth is that these are birds little known to science, probably due to their nocturnal habits, their cryptic plumage, and their elusive behavior.

    For example, while nightjars are thought to be able to tolerate disturbances to their natural habitats by human activities well, the effect that many environmental impacts could have on their conservation is unknown, especially when it comes to emission-related impacts. of chemical contaminants, As the metals.

    Thanks to a research project funded by the Seneca Foundation, a multidisciplinary team of scientists has evaluated the effects of exposure to certain non-essential metals – such as lead (Pb), cadmium (Cd), arsenic (As) and mercury (Hg), which are known to be toxic – on the physiology and physical condition of nightjars, using the red-necked nightjar as a study model (Caprimulgus ruficollis).

     

    The red-necked nightjar (Caprimulgus ruficollis) is a long-range migrant that winters in Africa, probably in areas west of the Sahara, traveling to the temperate regions of the Iberian Peninsula and North Africa during spring and summer to breed (Photo: Jose Manuel Zamora).

    The work was developed with the participation of the Research Groups in Toxicology, riding a Basic and Applied Zoology to Management and Conservation, And in Mediterranean ecosystems from the University of Murcia, the "Ulula" Association for Monitoring Night Birds, the Banding Group of the ANSE AssociationCluster "Effects of air pollution on birds" from the University of Turku (Finland) and the Research Group in Wildlife Toxicology of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM).

    The scientists studied specimens of nightjars exposed to three well-differentiated metal contamination scenarios depending on the human uses of the habitats they occupy during their summer stay in the Region of Murcia, in order to be able to establish comparisons. One of the scenarios was represented by habitats affected by the old metallurgical mining district "Cartagena-La Unión", which is currently abandoned and has never been restored or rehabilitated; another was characterized as a agricultural-urban area next to an industrial park; and a third scenario was represented by a natural space relatively free of anthropic pressure and environmental contamination, in order to be used as reference zone.

    In each one of the environmental scenarios several specimens of red-necked nightjars were captured, and for each one information was collected regarding their size and physical condition. Finally, before releasing them, the scientists took blood samples to analyze various biomarkers, which are "measurements" of certain physiological parameters that indicate the level of exposure of nightjars to environmental contamination (biomarkers of exposure) and/or whether said exposure is associated with negative repercussions on their health (biomarkers of effect).

     

    After collecting the blood samples and taking the morphometric data necessary for the investigation, the captured nightjars were returned to their natural environment (Photos: Silvia Espín).

    As expected, nightjars in the area affected by mining contamination had higher levels of As, Pb and Cd in their blood than the nightjars of the agricultural-urban zone and those of the reference zone. These exposure biomarkers indicate that abandoned mining waste in the former “Cartagena-La Unión” mining district, which was closed decades ago, remains a major source of environmental contamination today.

    In addition, various biomarkers of effect, such as blood levels of retinol (better known as vitamin A), uric acid y albumin, were lower in nightjars from the mining area compared to those from the other areas studied.

    If we take into account that vitamin A and uric acid are antioxidant substances, and that toxic elements such as Pb, Cd and As owe a good part of their harmful effects on health to the generation of oxidative stress –a physiological disorder that occurs when damaging free radicals win the battle against antioxidants–, the observed decrease in these parameters could be associated with metabolic and/or physiological alterations caused by exposure to high levels of environmental contamination.

    On the other hand, it must be considered that the decrease in albumin blood levels could indicate a diet lower in protein, which would be in accordance with the fact that the richness and/or abundance of insects –the nightjars' food– could be lower in the mining area due to metal contamination.

    To all this must be added the fact that the blood load of polluting metals was negatively related to physical condition nightjars in the mining area, an indicator that warns about their chances of survival. This negative relationship could be due both to the physiological wear and tear that nightjars in the mining area have to face to "detoxify" and to the fact that contaminated habitats might not be able to provide them with an adequate diet, either in quantity or quality. .

    Although more research is needed, the results of this scientific study as a whole seem to indicate that metal contamination could be a threat to conservation of the mysterious deceive shepherds in old mining areas.

    The scientific publication of this research is available at: