For the first time ever scientists have charted the genome of the golden eagle, and what they've found may shoot down one proposed way of making wind turbines safer for the huge birds of prey.
In a paper published Wednesday in the journal PLOS ONE, researchers described their work mapping the genetic makeup of a male golden eagle captured in the Tehachapi Mountains above the Kern County community of Caliente in December 2012. Researchers took a blood sample and fitted the eagle with a tracking collar, then released him.
When they sequenced the genetic material from the eagle's blood sample, the biologists learned that a commonly-held assumption about golden eagles' vision may not actually be true, a finding that might undermine one proposed method of warning off eagles from wind turbines.
For a number of years, some biologists have suspected that the golden eagle, Aquila chrysaetos, may be able to see wavelengths of ultraviolet light (UV) not visible to humans. This suspected ability would allow the raptors to hunt by looking for ultraviolet light reflected by mammal urine. That's led some to suggest that eagle mortalities could be reduced at wind facilities by coating turbine blades in paint that reflects ultraviolet light, which would in theory make them more prominently visible to the raptors.
A 2000 study published by the National Renewable Energy Laboratory (NREL) suggested that UV paint didn't make all that much difference in raptor mortality, but discussion has continued. This week's paper may offer an explanation for the 2000 NREL results.
The authors of the PLOS ONE study, led by biologist Jacqueline M. Doyle of Purdue University, found that the Caliente eagle didn't have a set of genes associated with the ability to see UV light. In birds and other vertebrates, an animal's range of color vision at the violet end of the spectrum is determined by a gene called the short-wavelength sensitive opsin gene, abbreviated SWS1. That gene controls the production of visual pigments that detect light with short wavelengths, in other words blue and violet.
Just as the gene that determines your blood type can have different varieties, called "alleles," that determine whether you have blood of type A, B, AB, or O, the SWS1 gene has different alleles that determine just how far into the UV end of the spectrum an animal can see.
Doyle and her colleagues found that the golden eagle's SWS1 opsin gene was of the allele that codes for visual pigments that can't register light with wavelengths shorter than 400 nanometers. That's about where human vision cuts off as well, which means that assuming the Caliente eagle's SWS1 opsin gene is typical of his species, which is quite likely, golden eagles can't see UV any better than we can.
That's bad news for wind turbine operators who were hoping to avoid violating the Bald and Golden eagle Protection Act by slapping UV paint on their turbine blades.
But as Doyle and her colleagues point out, it may be good news for smaller, UV-sensitive birds, who may well be able to signal each other with feather patches that reflect different shades of UV, giving them a visual language that's invisible to their golden eagle predators, and to us.
The eagle's genome also confirmed that the golden eagle is a relatively recent species, sharing common ancestors with other raptor species such as the peregrine falcon as recently as the Pliocene.
Oh, and that tracking collar? It revealed that once the eagle trapped in Caliente in 2012 recovered from its blood draw, it covered a huge swath of the state in its travels. The eagle's more than 400 square mile territory ranged from the Kern National Wildlife Refuge near Wasco to Tehachapi and Taft.