Migratory birds suffer from pesticides and insect decline
Neonicotinoids take a toll not only on insects, but also on birds. A study shows that migratory birds that ingest these pesticides are significantly weakened.
Migratory birds are under pressure. Climate change is shifting the seasonal availability of food, so that it no longer aligns with their travel schedule. Stopover sites are disappearing due to land use changes or are being altered by climate change. Migratory birds are also hunted, particularly in the Mediterranean region (read more about it here). And the massive use of pesticides in agriculture is causing insect populations to decline — insects that represent an important food source for many birds.
On top of all these problems, there appear to be direct health effects caused by pesticides from the class of neonicotinoids. Neonicotinoids are highly potent pesticides. When songbirds eat seeds treated with these pesticides, it impairs their migratory behaviour and, in the worst cases, even their survival. The neonicotinoid imidacloprid suppresses the birds' appetite and extends their stopover duration by several days. This makes songbirds more vulnerable to predators, and they also arrive at their destination late, potentially finding no mate.
Weight loss and delayed departure
The ingestion of realistic quantities of the insecticide caused the birds to eat less, lose weight, and depart later from their stopover sites — all within just a few hours — factors that impair their chances of reproduction and survival. In particular, birds exposed to the higher dose departed up to several days later, the researchers report in the journal «Science».
The administered quantities — 1.2 or 3.9 milligrams per kilogram of body weight — correspond to approximately 0.03 and 0.1 milligrams for a white-throated sparrow. «One treated maize kernel contains 1 milligram, and one rapeseed contains 0.17 milligrams of neonicotinoids», explains Livio Rey of the Swiss Ornithological Institute in Sempach. A seed-eater such as the white-throated sparrow would therefore have ingested the quantity used in the study very quickly.
The study underscores the importance of non-directly lethal effects of neonicotinoids on animal groups other than insects, Rey commented. The animals do not die directly from the amounts of insecticide ingested, but their organism is weakened by the poison and is therefore less well prepared for other challenges.
Earlier studies had already shown that these pesticides, which act as nerve agents, affect far more than just insects — they also affect birds and fish. Primarily because of their negative effects on pollinating insects such as bees, three plant protection products containing neonicotinoids are banned in Switzerland, including imidacloprid.
Long-lasting residues
However, the water-soluble insecticides are largely carried away as dust or by rain, entering soils and bodies of water far from the site of application. These substances are very persistent in such environments, as shown by a study conducted by the Swiss Ornithological Institute in Sempach and the University of Neuchâtel, among others.
For this purpose, they examined 100 cultivation areas and 69 biodiversity promotion areas (BFF) in the Swiss Plateau, managed conventionally (22 farms), according to IP-Suisse standards (20), or organically (20). All conventionally farmed areas showed residues of neonicotinoids. Even more concerning was the finding that all IP-Suisse-certified areas, 93% of organic areas, and over 80% of BFF were also contaminated with neonicotinoids, albeit at significantly lower concentrations. The contamination presumably originated from windblown dust or drift from conventional areas, or was carried in via ground or surface water.
Even on biodiversity promotion areas and on agricultural land that has been farmed organically for over ten years, neonicotinoid residues are found in the soil. There, insects, spiders, and worms were chronically exposed to pesticides. How great the damage from the direct health effects of neonicotinoids on bird populations is would be difficult to estimate, said Rey. The decline in insects and thus the loss of food also plays an important role. Given the challenges facing migratory birds in particular, however, the sublethal effects of neonicotinoids demonstrated in the study can also have a decisive impact.
«Given the growing body of evidence of the harmful effects of neonicotinoids on bees, fish, birds, and the environment in general, the central question is how the Federal Office for Agriculture could have approved such harmful pesticides in the first place», says Rey. «TheIn the past, it was the insecticide DDT that caused health damage far beyond insects. Today it is neonicotinoids, and after they are banned there will probably be new pesticides that also bring unwanted side effects.» He therefore advocates critically reviewing the approval processes for new plant protection products and tightening them if necessary.
