The United States is seeing a rapid decline in bird biodiversity with the bird population decreasing by 29 per cent since 1970, according to a new report.
In the paper published in Nature Sustainability, the researchers said that the population of grassland birds in the US has declined by 53 per cent.
Madhu Kanna, professor in Agriculture and Consumer Economics at University of Illinois and co-author of the paper was quoted as saying that the likely reasons for the rapid decline includes intensified agricultural production, conversion of grassland to agricultural land, use of pesticides and climate change.
Khanna said that several studies have shown neonicotinoids (nicotine-based pesticides) have negative effects on wild bees, butterflies and honey bees. However, large scale studies on the pesticide’s impact on birds have been limited.
She said that the study was the first comprehensive study at a national scale that took over seven years. The data from hundreds of bird species in four different categories – grassland birds, non-grassland birds, insectivores, and non-insectivores were looked into.
She said that there was much evidence of the negative impact of neonicotinoids, especially in grassland birds and to some extent on insectivore birds. The researchers analyzed bird populations from 2008 to 2014 with respect to changes in pesticide use and agricultural crop acreage.
They said in the paper that an increase of 100 kg in neonicotinoid usage per county (12 per cent increase on average) led to a 2.2 per cent decline in populations of grassland birds and 1.6 per cent in insectivorous birds. Meanwhile, the use of 100 kg of non-neonicotinoid pesticides led to a 0.05 per cent decline in grassland birds and a 0.03 per cent decline in non-grassland birds, insectivorous birds, and non-insectivorous birds.
The researchers noted that their findings showed that neonicotinoid use has a relatively large effect on declines of birds and that these impacts grew over time. They also noted that the impacts on bird populations were concentrated in Southern California, Midwest and Northern Great Plains.
The study showed that the effect of neonicotinoids could result directly from birds consuming treated crop seeds and indirectly by affecting the insect populations they feed on. They said that the consumption of a few seeds was enough to cause long term damage to the birds’ reproduction and development. Neonicotinoids are more toxic to insects and persist longer in the environment, the researchers note.
With respect to intensified agricultural production and conversion of grassland to agricultural land, the researchers pointed out that it also contributed to the decline. While the use of other pesticides has been flat or declining, neonicotinoid usage has grown exponentially over the past two decades.