Orange balls

Everytime I drive I-89, I notice those bright orange balls attached to the power lines that cross the interstate to the Bolton Falls Hydro Station (map). It seems an odd marker as there are plenty of other places where power lines cross the interstate or other major roads but aren’t adorned with these plastic orange ornaments. Not surprisingly, the visually obvious orange balls, called power line marker balls, are intended to make power lines visually obvious to pilots, particularly in places where airplanes and helicopters tend to fly at low altitudes (like around airports, mountain passes, deep valleys, or even on larger bodies of water where a float planes might land). The balls were invented in the early 1970s by Arkansas governor, Winthrop Rockefeller, who noticed their potential danger during the landing of a flight with Arkansas’ head of the Department of Aeronautics. 

Bird Balls on I-89 near Bolton Falls

The FAA specifies the dimensions (36” diameter over lakes, canyons, and rivers, 20” when close to an airport or on lines lower than 50’), color (orange, yellow, or white), and spacing (200’ intervals or 30-50’ when near the end of a runway) of marker balls. And they’re not cheap either. The basic models run anywhere from around $200-1000 each, with more advanced models that come equipped with lights running upwards of $2,000 each (here’s a catalog in case you’re looking to decorate your tree with something extra gaudy this year).

Bird ball attached to a powerline (from Wikimedia)

Birds and Powerlines

Marker balls may have been invented to protect pilots from power line collisions, but avian aviators have also benefited as power lines can be fatal to birds passing through or over them. So while a bird can perch on a wire without problem (link), problems arise when their wings connect the voltage running through two different wires, causing electric to shoot through the bird’s body. At the species level, bird-power line collisions might not be a significant contributor to total death rate, but collisions are not an uncommon occurrence and on a local level can be a significant source of mortality.

Gray catbird perched on an electrical wire (Rock Point, Burlington)

Larger birds like cranes, pelicans, flamingos, and waterfowl are disproportionately affected because their wings can span the gap between lines (source, here’s a video snow geese flying into a power line, viewer discretion advised). During migration, death rates at unmarked lines can be as high as 21 deaths for every 100,000 birds flying among or over power lines. This can add up for something like snow geese whose total population exceeds 15 million birds. In one study (source), power line collisions were the #1 cause of mortality for fledged whooping cranes, accounting for over a third of all deaths! 

These collisions, which are almost always fatal to the birds, regularly cause power disruptions. Entergy, a utility company in the south, estimates that more than 22,000 of its outages in Mississippi were caused by animals; 1,200 of these were attributed to birds (link). And there are countless news stories about avian-caused outages, like one back in September where a great blue heron flew into a power line in Greeneville, CT and knocked out power for 12,000 people for two hours (link). Markers of various sorts (the marker balls used for pilots aren’t the only types of deterrents power companies use) can greatly reduce the risk to birds. A study in South Africa found that markers reduced mortality by 50-60% (source), which was consistent with other studies (e.g. this one on migratory birds in Spain: source). Most powerlines are not marked, partly because this would be cost-prohibitive. So on behalf of the birds, thanks to those power lines that are equipped with markers and to Winthrop Rockefeller who invented the humble yet mighty orange power line marker ball!

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