This is an unpublished study. It shows, from the observation of birds in the wild, that those who live near organic farming fields are in better health than those living in conventional farming landscapes.
The article, titled Organic farming has a positive effect on the vitality of passerines in agricultural landscapeswas published at the end of May in the journal Agriculture, Ecosystems & Environment.
According to its authors, their study stands out in two ways. “ Most of the studies that compare organic and conventional are mainly biodiversity analyses: we see that there are fewer different species and less density of individuals of each species depending on the area. »explains to Reporterre Jérôme Moreau, researcher at the Biogeosciences laboratory of the University of Burgundy and first author of the study. Otherwise, “ the vast majority of studies on the effects of pesticides on wildlife are pure toxicology, animal models in captivity are used to assess the effects of certain substances »completes its co-author Vincent Bretagnolle, researcher at the Chizé laboratory (Deux-Sèvres) of CNRS.
In the laboratory, a particular substance is tested in very high doses. There, it is the exposure of birds to pesticides in real conditions that has been observed: the doses are much lower, but the molecules are much more numerous. “ In our area, we have identified 300 different pesticide moleculescontinues Vincent Bretagnolle. We do not find which molecule is incriminated. But we measure the real effect of exposure to a cocktail of pesticides. »
Birds “ apathetic, amorphous »
This research in the natural environment was possible thanks to a particular device, the “ Zone Atelier Plaine and Val de Sèvre ». This large territory south of Niort (Deux-Sèvres), where there are 435 farms in particular, has been documented for almost thirty years by scientists from the Chizé laboratory, who work with farmers. “ Everything is inventoried: if the field is organic or conventional, what types of pesticides are used and in what quantities they are applied », explains Jérôme Moreau. This precision made it possible to determine 10 hedges in the middle of mainly organic fields, and 10 hedges in a predominantly conventional landscape.
The researchers then placed nets to capture the birds. They were to spend no more than ten minutes in the net, with an experimenter quickly arriving to perform a series of four simple tests. Only observations made on the six most caught species  were selected in order to have a significant sample.
“ It is a systemic problem, linked to the environment. »
The result was clean. “ Escape attempts, aggressiveness, pecking and cries of distress during capture […] were all higher in birds captured in organic hedgerows than in those captured in conventional landscapes »note the researchers in their paper. “ It was as if birds taken from conventional fields were apathetic, amorphous »says Jérôme Moreau.
Such clarity of observations surprised the researchers themselves. “ We are a priori on very low doses of pesticidesnotes Vincent Bretagnolle, on passerines which live for a very short time, one or two years. And many of which belong to migratory species, exposed for only three months. I did not expect that we would find a difference on all species and practically all parameters. The signal is very strong. » “ Our study observes almost the same result in all the species on which we have workedadds Jérôme Moreau. This shows that it is a systemic problem, linked to the environment. »
“ An early warning signal »
Scientists rule out that the difference in behavior can be attributed to different availability of food in different landscapes, “ because the body condition [des oiseaux] was identical in both contexts », says the article. They also began to identify and quantify pesticides in the blood of birds, to clarify the link of cause and effect.
To explain the poor health of birds living in conventional landscapes, Vincent Moreau puts forward several hypotheses. “ First, the birds are much less alert and detect the predator later. We can imagine nervous problems, because we know that certain molecules of pesticides have this type of effect. The other hypothesis is that the energy put into detoxifying pesticides is not put into running away from the predator. »
- Among the species studied: blackcaps. Flickr/CC BY–CN–n/a 2.0/eng298
These results reinforce those published by the same team a year ago. She had then studied caged birds, partridges, half fed with cereals from conventional agriculture, and the other from organic farming. They had already noticed “ spectacular effects ». For example, partridges fed conventional grain laid fewer eggs and smaller eggs. The males had less visible attributes of seduction during the mating period. They had also shown a weakening of the immune defenses, therefore a probably greater difficulty in reacting to predators.
The results of these two studies “ open a field of research on the sublethal effects of pesticidesbelieves Vincent Bretagnolle. There are important consequences on the behavior, physiology and ecology of these species. It would be necessary to look in humans, the studies have not yet been done ».
The idea is to continue to carry out research in real conditions, at the scale of the ecosystem, in this “ workshop area » of Deux-Sevres. “ We will compare the exposure to pesticides of inhabitants in villages surrounded by organic or conventional agriculture. », he said. The health of the birds will also be observed.
Jérôme Moreau believes that our winged companions could be a “ early warning signal » environmental degradation in agricultural areas. Changes in bird behavior are observed even at very low doses of pesticides. It is therefore a very sensitive indicator. “ Measuring bird behavior, as we have done, is quite simple. We could do it in many other environments in France, which would allow us to say if they can also be dangerous for humans. »