From ABC News
TV and radio towers, blamed for nearly 7 million bird deaths each year in North America are doing the most damage to species that can hardly afford the loss, according to a new study published in Biological Conservation.
In the United States and Canada, at least 97% of the birds that crash into the towers, or the guy wires that hold them up, are the tiny songbirds – mostly warblers – that are considered “birds of conservation concern”.
The latest study comes from the same researchers, members of the Los Angeles-based Urban Wildlands Group, that warned last year of the spiralling mortality of birds that are attracted to the lights, usually red, atop the towers. The lights are required by the USA’s Federal Aviation Administration (FAA) for any tower over 200 feet tall, and there are thousands in North America that are more than 10 times that height.
The deaths usually occur during the nocturnal migration of songbirds, especially when the cloud ceiling is low and there is fog or rain. The lights create an illuminated area around the tower and it is thought the birds become confused, switch off their night navigation and begin to spiral around the tower. Some run into the support cables, or into each other, and plunge to the ground.
Travis Longcore, from the University of Southern California and lead author of the current study, said his group wanted to look beyond the sheer numbers and focus on which types of birds were suffering the greatest loses, based chiefly on the number of deaths compared to the overall population estimate of each species.
“Many bird species are killed at towers disproportionate to their abundance,” the study says.
“This lets us look at this (the tower deaths) as a factor in the trajectory of the population”. The study indicates that towers are a very significant factor for a number of species, especially small songbirds, some of which are declining in numbers overall. The researchers found that 58% of the birds killed each year are warblers, including Swainson’s warbler Limnothlypis swainsonii, which loses 8.9% of its population each year, and the black-throated blue warbler Dendroica caerulescens loses 5.6%. It’s not just songbirds though, each year yellow rail Coturnicops noveboracensis loses about 9% of its total population because of communications towers, many of which are taller than the Empire State Building.
In addition to communications towers, however, the birds have to fend off cats and other predators, and many are killed when they crash into windows, as urban dwellers know so well. So towers are only part of the problem, but this study suggests they may be more significant than had been thought, at least for certain species.
Some recent experiments have shown that a flashing (blinking) light attracts fewer birds than a light that remains on. The FAA recently ruled that tower operators may switch to blinking lights, and some have done so. It could be too that when a steady light is replaced by a blinking light, the birds simply leave. This is not an expensive modification but the results may be immediate.
This research is, of course, based on estimates, some of which wildly disagree with estimates from other researchers, and that may be partly because the situation varies so dramatically across the country. And just simply collecting the data is difficult. Longcore pointed out that a dead bird doesn’t hang around very long.
“Scavengers and predators and decomposers are incredibly effective,” he said. In one case an owl was spotted as it zipped through the night sky and grabbed small birds before they even hit the ground.
However, sometimes it’s easier to find how many birds have died. Scientists found that an estimated 5,000 to 10,000 birds, mostly Lapland Longspurs, were killed on Jan. 22, 1998, near a 420-foot tower in western Kansas. It happened, as is often the case, during a heavy snowstorm. See bibliography of bird kills in USA here
And the number of kills from towers still lags far behind the estimated number of deaths caused by birds hitting windows. And still, the estimates vary widely. One group of researchers, for example, estimated that the number of window-kills was somewhere between 97.6 million to 976 million annually.
Longcore said he believes that if most towers are modified, just by switching to flashing lights, many more songbirds will be around to serenade us in our gardens.
The situation with tall masts in the Channel Islands is unclear. However, there are such things such as those on the north coast of Jersey and this may be an area for future research.