Bird species have evolved all sorts of specialized beaks for their respective dietary niches, but not birds of prey.

According to new research out of England, raptors, eagles and hawks have missed out on the perks of a specialized pecker.

Of course, the beaks of these skilled predators are capable of doing their job -- tearing apart the flesh of fresh prey. They have simply benefited from the arms race in the manner that other species have.

The proof, researchers say, is in the patterns of evolution and adaptation.

Birds that fish or pry insects out of tree holes have evolved beaks independent of skull shape and size. Models cannot predict most bird species' beak shape and size based on other anatomical features. The same can't be said for birds of prey.

"Our results show that in birds of prey such as eagles and falcons, the shapes of the skulls change in a predictable way as species increase or decrease in size," Jen Bright, a researcher at the University of Sheffield, said in a news release. "The shape of the beak is linked to the shape of the skull, and these birds can't change one without changing the other."

Bright is the lead author of a new paper on the subject, published this week in the journal PNAS.

"We think that being able to break this constraint -- letting the beak evolve independently from the braincase, may have been a key factor in enabling the rapid and explosive evolution of the thousands of species of songbirds such as Darwin's finches and Hawaiian honeycreepers," added Bright.

The findings don't discredit Darwin's theories on evolution. Bird of prey benefit from adaptation, but the evolution of their beaks have been constrained.

"Basically, if you're a bird of prey and you're small, you look like a tiny falcon, and if you're a bird of prey and you're large, your skull looks like a vulture," explained study co-author Jesus Marugan-Lobon, a researcher at the Autonomous University of Madrid.