When birds molt, they shed old, worn feathers and replace them with new ones. While studying dozens of Great Gray Owls in Wyoming, TRC Field Biologist Katherine Gura documented something unusual about how these birds molt: instead of replacing their tail feathers gradually like most birds do, Great Gray Owls lose their whole tail at once. Katherine Gura studied dozens of Great Gray Owls to identify tail molting patterns and published her findings in the Journal of Raptor Research. Great Gray Owls molt their tail feathers rapidly over a few days, either in no particular order or from the center feather outwards, in a process called synchronous molting. This means that a Great Gray Owl can appear tail-less for up to a few weeks while the new feathers grow in! Katherine found that most Great Gray Owls molt their tails between late June and early August. No individual studied had tail feathers more than one year old, indicating that most Great Gray Owls molt their entire tail every year. If you see an adult Great Gray Owl that appears to have no tail feathers, there is no need to worry about the bird; you are witnessing the natural molting process.
The advantages and implications of synchronous tail molt in large owls are not well understood. Great Gray Owls likely can afford a synchronous tail molt because they employ a perch-and-pounce hunting strategy that requires minimal use of their tail for maneuvering. We anecdotally observed no obvious flight impairment by an owl that had molted all of its tail feathers. Other studies have shown little or no loss of maneuverability in Northern Spotted Owls and Burrowing Owls that molted all of their tail feathers at once. Great Gray Owls probably molt between late June and early August because northern pocket gophers are most abundant at this time. Growing new feathers requires a lot of energy, so it is advantageous for owls to molt when they can easily find a lot of prey. Northern pocket gopher populations vary less from year to year than other prey species, such as voles, so Great Gray Owls molt their tails when they can rely on pocket gophers to be abundant.