Almost seven million birds perish at communication towers in North America each year

Every year nearly 7 million birds die as they migrate from the United States and Canada to Central and South America, according to a new USC study published on April 25 in the journal PLoS ONE.

The birds are killed by the 84,000 communication towers that dot North America and can rise nearly 2,000 feet into the sky, according to the authors of "An Estimate of Avian Mortality at Communication Towers in the United States and Canada."

Placing that figure in context, the Exxon Valdez oil spill killed 250,000 birds and the Empire State building is 1,250 feet high.

"This is a tragedy that does not have to be," said lead author Travis Longcore, associate professor in the USC Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences.

The taller the tower the greater the threat, the study found. The 1,000 or so towers above 900 feet accounted for only 1.6 percent of the total number of towers. Yet these skyscraper towers killed 70 percent of the birds, about 4.5 million a year, Longcore said.

Most of the birds spent winter in places like the Bahamas and summer in Canada. With names like the Common Yellowthroat and the Tennessee Warbler, they could fit in the palm of one's hand.

"These birds eat insects and keep our forests healthy," Longcore said. "They are quite beautiful. We have a long history of appreciating birds. Millions of people watch birds."

However, the birds are not generally killed by running into the tower itself but the dozens of cables, known as guy wires, that prop up the thin, freestanding structure, Longcore said.

During bad weather, the birds were pushed down by cloud cover and flew at lower altitudes. The clouds also removed navigation cues, such as stars, leaving only the blinking or static red lights of towers.

The blinking did not fool the birds, but towers with a static red light resulted in more dead birds.

Estimated annual avian mortality from communication towers by Bird Conservation Region. High mortality estimates in Peninsular Florida and Southeastern Coastal Plain reflect the more numerous and taller communication towers in these regions.

"In the presence of the solid red lights, the birds are unable to get out of their spell," Longcore said. "They circle the tower and run into the big cables holding it up."

Longcore estimated that changing the steady-burning lights on the 4,500 towers greater than 490 feet tall (about 6 percent of the total) could reduce mortality about 45 percent, or about 2.5 million birds. The study also recommended that businesses share towers to reduce their number and build more freestanding towers to reduce the need for guy wires.

In 2005, Longcore and his colleagues started collecting and analyzing data from field studies that counted the number of bird kills at communication towers across the United States. The team only used findings that documented bird kills for at least a year and in some cases for several decades.

The numbers were scrutinized to find the average bird mortality based on height, the guy wires and the types of lights affixed to the tower.

The team then matched up tower types, sizes and attributes of 38 tower studies, applying those findings to the 84,000 towers across Canada and the United States in preparation for the new publication, which also was submitted to the Federal Communications Commission.

"One of the things this country has been great about is saying we care about not losing species on our watch," Longcore said. "With these towers, we are killing birds in an unnatural way. This is senseless."

The study, which does not include shorter towers that typically are used for mobile telephone transmission, focused on towers taller than 180 feet, which typically provide TV and radio frequencies.

The study's authors included Catherine Rich and Beau MacDonald of The Urban Wildlands Group, Pierre Mineau, Daniel G. Bert and Erin Mutrie of Environment Canada, Lauren M. Sullivan of UCLA, Sidney A. Gauthreaux of Clemson University, Michael Avery of the U.S. Department of Agriculture/Wildlife Services, Albert M. Manville of U.S. Fish and Wildlife Service, Emilie Travis and David Drake of the University of Wisconsin and independent scholar Robert L. Crawford.

The study was funded in part by The Urban Wildlands Group, Environment Canada, the American Bird Conservancy and Defenders of Wildlife.

Shrinking helped dinosaurs and birds to keep evolving

Although most dinosaurs went extinct 65 million years ago, one dinosaur lineage survived and lives on today as a major evolutionary success story -- the birds.

An Oxford University-led team studied how dinosaurs evolved into a huge range of shapes and sizes over 170 million years. Shrinking their bodies may have helped the group that became birds to continue exploiting new ecological niches throughout their evolution.

A study that has 'weighed' hundreds of dinosaurs suggests that shrinking their bodies may have helped the group that became birds to continue exploiting new ecological niches throughout their evolution, and become hugely successful today.

An international team, led by scientists at Oxford University and the Royal Ontario Museum, estimated the body mass of 426 dinosaur species based on the thickness of their leg bones. The team found that dinosaurs showed rapid rates of body size evolution shortly after their origins, around 220 million years ago. However, these soon slowed: only the evolutionary line leading to birds continued to change size at this rate, and continued to do so for 170 million years, producing new ecological diversity not seen in other dinosaurs.

A report of the research is published in PLOS Biology.

'Dinosaurs aren't extinct; there are about 10,000 species alive today in the form of birds. We wanted to understand the evolutionary links between this exceptional living group, and their Mesozoic relatives, including well-known extinct species like T. rex, Triceratops, and Stegosaurus,' said Dr Roger Benson of Oxford University's Department of Earth Sciences, who led the study. 'We found exceptional body mass variation in the dinosaur line leading to birds, especially in the feathered dinosaurs called maniraptorans. These include Jurassic Park's Velociraptor, birds, and a huge range of other forms, weighing anything from 15 grams to 3 tonnes, and eating meat, plants, and more omnivorous diets.'

The team believes that small body size might have been key to maintaining evolutionary potential in birds, which broke the lower body size limit of around 1 kilogram seen in other dinosaurs.

'How do you weigh a dinosaur? You can do it by measuring the thickness of its leg bones, like the femur. This is quite reliable,' said Dr Nicolás Campione, of the Uppsala University, a member of the team. 'This shows that the biggest dinosaurArgentinosaurus, at 90 tonnes, was 6 million times the weight of the smallest Mesozoic dinosaur, a sparrow-sized bird called Qiliania, weighing 15 grams. Clearly, the dinosaur body plan was extremely versatile.'

The team examined rates of body size evolution on the entire family tree of dinosaurs, sampled throughout their first 160 million years on Earth. If close relatives are fairly similar in size, then evolution was probably quite slow. But if they are very different in size, then evolution must have been fast.

'What we found was striking. Dinosaur body size evolved very rapidly in early forms, likely associated with the invasion of new ecological niches. In general, rates slowed down as these lineages continued to diversify,' said Dr David Evans at the Royal Ontario Museum, who co-devised the project. 'But it's the sustained high rates of evolution in the feathered maniraptoran dinosaur lineage that led to birds -- the second great evolutionary radiation of dinosaurs.'

The evolutionary line leading to birds kept experimenting with different, often radically smaller, body sizes -- enabling new body 'designs' and adaptations to arise more rapidly than among larger dinosaurs. Other dinosaur groups failed to do this, got locked in to narrow ecological niches, and ultimately went extinct. This suggest that important living groups such as birds might result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years, which could not be observed without fossils.

'The fact that dinosaurs evolved to huge sizes is iconic,' said team member Dr Matthew Carrano of the Smithsonian Institution's National Museum of Natural History. 'And yet we've understood very little about how size was related to their overall evolutionary history. This makes it clear that evolving different sizes was important to the success of dinosaurs.'