A Curious Commensalism: The Screech Owl and the Texas Blindsnake
It may be small, but the eastern screech owl is a formidable hunter. Its prey – whether rodent, bird or reptile – rarely survives the raptor's strike.
But in the mid-1980s, two Texas biologists found an exception. Owls were carrying live snakes to their nests – Texas blindsnakes, to be specific.
Why would a screech owl want a blindsnake as a house guest? Scientists suspect an unusual symbiosis between the two species.
The eastern screech owl is found across the eastern half of the United States. The Llano Estacado is at the western limit of its range. The small, agile predator – standing at less than 10 inches high – nests in trees and can thrive in West Texas cities and in the countryside.
And the Texas blindsnake? It's found across the American Southwest and northern Mexico. But this curious serpent escapes the notice of most of us.
The blindsnake is “fossorial” – meaning it lives most of its life underground, Michael Nickell, museum scientist at the Sibley Nature Center in Midland, said.
“They feed underground, and they mostly live underground,” Nickell said. “But when it does rain they will come to the surface, and at night they will come to the surface, looking for the type of insects they feed on – which is usually the larvae of ants and termites and other soft-bodied insects.”
The blindsnake is gray and slender, up to 8 inches long. You could mistake it for a shiny earthworm. As its name suggests, the snake is essentially blind, with tiny, vestigial eyes. Its tightly connected scales armor it for assaults on ant colonies.
In the 1970s and 80s, Baylor University researchers Fred Gehlbach and Robert Baldridge were studying screech owl nesting ecology near Waco, Texas. Screech owls are known to prey on blindsnakes. But the two scientists saw the owls were carrying live blindsnakes to their nests.
The researchers were studying the owls in more than 70 experimental nest boxes. They found that 14 of those nests contained live blindsnakes. In some nests, there were as many as 15 snakes living among the owl chicks.
“The snakes would slither down into the lower realms of the nest,” Nickell said, “where all the gunk was, the fecal matter, the decaying meat – that was harboring flesh-eating flies, things that are nest parasites and could adversely affect the health of the developing owlets. It turns out these snakes were feeding on that stuff.”
Had the screech owls simply failed to finish off the snakes as prey, or did they let them live in the nests for a reason? Whatever the reason, these live-in housekeepers benefited the owls.
“It turns out that the owlets from the nest that had the snakes in them, they grew faster, they grew bigger, and they were healthier than the ones without the snakes,” Nickell said. “Once the owls fledged and flew off, the snakes found their way back to the ground.”
In nests with blindsnakes, owlets were 25 percent more likely to survive. Some of these baby owls grew as much as 50 percent faster.
The observations suggest a form of symbiosis known as as “commensalism” – in which one party is benefited, while the other is unaffected.
“What did the snakes get out of it?” Nickell said. “Well, they weren't harmed, but they really weren't benefited either – so this could possibly be a commensal-type relationship between the eastern screech owl and Texas blindsnakes.”
The Baylor researchers have been the only ones to study this apparent symbiosis. How widespread is it? Both species are at home on the Llano Estacado – do they cohabit here?
Could the relationship exist between blindsnakes and western screech owls, which are found in the Trans-Pecos? And what cues or instincts allow an owl to identify a blindsnake as beneficial?
“For every question you answer in science, it raises 10 others,” Nickell said. “There's so much out there yet to be discovered in this world.”
One thing is certain: The relationships among the wildlife that surround us are more complex than we imagine.