Lack of shelter and the large amount of food available from crops in the mid-valley of the Ebro reflect primarily how human beings influence the landscape, and the demography and reproduction of wild boar. Wild boar living in the Ebro Valley do not survive for as long as those living in the Pyrenees. These are the conclusions of a study carried out by a team of Spanish ecologists.
In the Aragonese Pyrenees the population of wild boar (Sus scrofa) live in large, continuous areas of forest, where food sources are unpredictable. However, the population of wild boar in the mid-valley of the Ebro lives in a system of intensive farming that has been transformed by humans, and is characterised by thickets where there are few areas for shelter but large amounts of food, basically consisting of crops.
This is what has led Juan Herrero, a teacher from the University of Alcalá, Madrid, and his team, to carry out a study to prove that the presence of humans can change a species’ demography.
In order to carry out the study, which has been published in the journal entitled Acta Theriologica, the researchers have relied on the help of groups of hunters and financial support from the Aragón Government. The team analysed the populations of wild boar from1990 to 1993 in the Pyrenees, and from 1994 to 2006 in the Ebro valley. Herrero points out an important detail to SINC: “The animals that have been hunted have enabled us to deduce that to a great extent the structure and reproduction of the populations depend on us”.
Food and shelter are key parameters
In the mid-valley of the Ebro where there are few options for shelter and food is plentiful, the animals have a low life expectancy of 6 years, whereas in the Pyrenees this is 10 years. The female wild boar reproduces at the end of the first year of life, that is to say one year before the others. “In populations that depend on very small areas of shelter, such as the Ebro Valley, hunting makes an impact” explains the scientist.
Hunting does not interfere specifically in the reproduction of wild boar in the Ebro valley, but the conditions in which the wild boar populations live do have an influence. There are very few areas for shelter in the Reserva Natural de Los Galachos in Zaragoza, and they are surrounded by an area of intensive farming. “The animals protect themselves in the thickets but come out to feed among the crops”, adds Herrero.
Although in the Reserva Natural de Los Galachos hunting is prohibited in particular, damage to crops has made it essential to carry out population checks over the last several years. As there are few areas for shelter “although only a few wild boar are hunted, overall the pressure from hunting is great”, emphasises Herrero.
The high availability of food in the mid-valley of the Ebro engenders “a very exceptional situation for a natural population”. According to the researcher, “it seems completely artificial, as if we were giving them unlimited amounts of food”. Added to this is the absence of shelter, which prevent the animals from coming up against hunters who alter their rise in numbers, productivity and life expectancy.
Setting up and implementing this research has not been an easy task. Herrero states that it is difficult to set up monitoring programmes and studies for the species that are abundant and do not seem to have any problems, “because the species that are threatened are more important”. The researcher states that “there always has to be a very specific problem for anything to be done”.
Although Aragón is the region of Spain where higher numbers of wild boar are killed during the hunting season (nearly 25,000 every year) and millions are hunted in Europe, there does not seem to be a reduction in population.
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