Over 200 million red-winged blackbirds are believed to live in the US
Mass animal deaths have been in the news the past week or two and the specific cause of many remains a mystery.
But most naturalists are not ready to press the panic button.
It’s an unfortunate fact that mass animal deaths often occur in nature, particularly during stressful periods such as cold snaps or natural disasters. To most experts following the news, the numbers in recent reports are not particularly alarming. As a frame of reference, there are probably 20 billion (estimates vary widely) wild birds in the United States and ornithologists estimate that bird mortality exceeds 5 billion birds annually. Given those numbers, most of the reported incidents appear modest in scale and are consistent with previously observed events.
A typical Atlantic hurricane may cause the deaths of hundreds of thousands of birds. While it’s not a particularly pleasant statistic, that’s the way nature works.
Several recent incidences of groups of red-winged blackbirds being found dead appear to have been caused by the birds encountering obstacles while flying in the dark, which they don’t normally do. Reported mass deaths of blackbirds in Arkansas and Lousiana were noticed immediately after holiday fireworks displays. It’s entirely possible that the birds were startled by the fireworks, flying off into the night and into trees, power lines and other birds. Necropsies (autopsies on animals) performed on the birds found in Arkansas showed extensive blunt force trauma to the birds, consistent with them flying into objects.
On a side note, collisions with objects such as buildings, power lines and radio antennae are a leading cause of bird mortality. Toronto’s Fatal Light Awareness Program (FLAP) estimates over one million birds perish annually from hitting the city’s skyscrapers while flying.
There have also been several fish kills reported in the past few weeks as well. In these instances, the cause is most likely winter’s cold. The East in particular has been experiencing a colder than normal winter to date. One large fish die-off was reported in the upper Chesapeake Bay and was primarily of spot, a species known to be sensitive to cold. There have been large die-offs of spot reported during previous cold winters on the Chesapeake.
A similar episode has recently come to light in Lake Michigan near Chicago as well, this time with Grizzard shad. As with the Chesapeake’s spot, this species of shad is known to be more sensitive to cold than many other fish species.
So it’s most likely a combination of timing and unusual press coverage that’s brought these recent die-offs to the public’s attention. There’s no shortage of threats to wildlife, so naturalists and state wildlife officials are always keeping an eye on our wildlife populations and continue to look for unusual trends in wildlife mortality.
And we’ll keep you informed here at eNature as we learn more.
Updated Wednesday, 1/2/10 with additional external links.