Scientists said that the mass death of thousands of birds, including flycatchers, swallows and warblers in the South-western US was caused by starvation, which became worse due to the cold weather probably linked to climate change.
These birds fell from the sky in September and many people found the carcasses in the regions like New Mexico, Texas, Arizona, Colorado and Nebraska. But after conducting the necropsy by the USGS National Wildlife Health Center, 80 percent of the specimens showed signs of long-term starvation. However, the rest 20 percent of the dead birds were not in a good condition to conduct proper tests.
According to the scientists, it was also noticed that muscles controlling the birds' wings were shrunken, they also lost overall body fat, kidney failure and blood was found in the intestinal tract.
Jonathan Sleeman, director of the USGS National Wildlife Health Center in Madison, Wisconsin, said that "it looks like the immediate cause of death in these birds was emaciation as a result of starvation". According to him, it is possible that the weather event forced these birds to migrate when they were not ready, or maybe "impacted their access to food sources during their migration".
Most of the birds died between September 9 and 10. Many birds appeared lethargic and were congregating in groups before dying. Some birds were found to be disoriented, flying into cars and buildings. Martha Desmond, a professor in the biology department at New Mexico State University (NMSU), who collected carcasses, said her team was not talking about short-term starvation, but this is "a longer-term starvation." He explained these birds became so emaciated that they actually had to turn to wasting their major flight muscles and this doesn't happen overnight.
Desmond said that the birds probably began migrating when they were in poor health condition and that could be related to the mega-drought in the southwest of the US. The expert added that since they are expecting to have more dry years in New Mexico, "it appears that a change in climate is playing a role in this and that we can expect to see more of this in the future". Even though Sleeman could not confirm whether this long-term starvation is directly related to climate change, he said that the dramatic environmental changes are making extreme weather events more likely.
However, Desmond's team is hoping to get funding to support more research into such alarming incidents involving birds so that they can better monitor what is happening. Sleeman said large-scale mass mortality wildlife events were frequent and it is something that needs to keep track of.