This is the result of an analysis, the results of which the scientists led by Ryan Shipley from the water research institute Eawag report in the journal “Current Biology”. For more than two decades, he and his team studied the insect abundance and breeding season of seven species of songbirds and migratory birds that feed insects to their offspring in the northeastern United States.
Unlike insects that live on land, aquatic insects are rich in long-chain omega-3 polyunsaturated fatty acids. They are therefore a particularly valuable source of food for young birds. However, the period when there is an abundant supply of aquatic insects has shortened and the breeding season has been brought forward, said ornithologist Shipley, according to an Eawag statement. Global warming is to blame.
The data showed that aquatic insects appear about a week earlier in spring than they did in the 1990s, and for terrestrial insects it is almost two weeks. Bird species that do not start breeding until mid-May therefore almost exclusively find terrestrial insects on the buffet. Only: Birds, which depend on healthy aquatic insects to meet their nutritional needs, cannot simply switch to terrestrial insects.
The postponed availability of food was reflected in the number of birds because they could not move their breeding season forward enough. Early breeders like the blue-throated warbler now appear to be benefiting. Their population has increased in the study area since 1966, as Eawag explained. Unlike the marsh martins that breed later. Their number has decreased.
The results cannot be transferred one-to-one to other areas. According to the experts, however, it is likely that insect development and bird breeding seasons have also shifted and decoupled in Central Europe. To explore this more closely, Shipley is now planning a larger-scale study with data from Europe, Russia and Japan.
https://www.cell.com/current-biology/fulltext/S0960-9822(22)00119-1