For owls, what goes down must come up

Rappahannock News - - NATURE - PAM OWEN wil­ © 2018 Pam Owen

With not a lot of wildlife or plant ac­tiv­ity go­ing on this time of year, I of­ten look to the de­tri­tus on the to see if some­thing in­ter­est­ing catches my eye. Not long ago I came across an oval-shaped wad of fur that I’ve wanted to come across for years — an owl pel­let.

The wad of hair was about two inches long and oval. On closer in­spec­tion, I could see a bone frag­ments mixed in with the hair. If it is in­deed an owl pel­let, it prob­a­bly came from an east­ern screech-owl (Me­gas­cop­sasio) that’s been do­ing its dis­tinc­tive whin­ny­ing call down in that area for months.

Rap­tors, such as owls, and a few other bird species deal with the nondi­gestible parts of their prey — in­clud­ing bone, teeth, hair, feath­ers and ex­oskele­tons — dif­fer­ently from most birds. Most birds, in­clud­ing other rap­tors, also have a crop, which is a food-stor­ing pouch that is cre­ated by the ex­pan­sions of mus­cles in the esoph­a­gus, owls do not. But east­ern screech-owls can cache food in tree holes for as long as four days, ac­cord­ing to All About Birds (­cree­chowl), a Cor­nell Lab of Or­nithol­ogy web­site.

With owls, the food goes di­rectly to the giz­zard, at the rear of the stom­ach, which is an organ unique to birds. There di­ges­tive flu­ids, mixed with hard, rough ma­te­ri­als such as small stones the bird has picked up, dis­solve and grind up the food. The soft tis­sue is then sent to the in­testines to be fur­ther bro­ken down and the nu­tri­ents ab­sorbed. Small amounts of tis­sue that is not ab­sorbed, along with other bod­ily waste, is ex­creted through the owl’s vent, in its rear end.

The larger in­di­gestible parts of the prey are formed into a slimy pel­let, which through strong con­trac­tions in the giz­zard, the owl ex­pels out of its mouth. This process is known as “eges­tion,” which is unique to birds. It dif­fers from the re­gur­gi­ta­tion process of mam­mals, which comes from the con­trac­tion of ab­dom­i­nal mus­cles. Owls gen­er­ally feed early in the evening and ex­pel a sin­gle pel­let about 20 hours later.

While the process does not sound pretty, the pel­lets are like lit­tle trea­sure chests for the na­ture-cu­ri­ous and ster­il­ized pel­lets are used in schools to teach kids about what owls eat. Al­though most bones are usu­ally pre­served, they are of­ten mixed with parts of other prey.

With east­ern-screech-owls, the diet is quite di­verse, ac­cord­ing to All About Birds: Most kinds of small an­i­mals, in­clud­ing mam­mals such as rats, mice, squir­rels, moles, and rab­bits and even bats are on the menu. Other prey in­clude small birds, such fly­catch­ers, swal­lows, thrushes, waxwings, and finches, as well as larger species, in­clud­ing jays, grouse, doves, shore­birds and wood­peck­ers, some­times strip­ping off feath­ers be­fore con­sum­ing the rest. Even iden­ti­fi­ca­tion bands for birds have been found in owl pel­lets.

East­ern screech-owls also eat “sur­pris­ingly large numbers” of cray­fish, frogs and tad­poles, lizards, along with in­sects, earth­worms and other small in­ver­te­brates, ac­cord­ing to All About Birds. In fact, “data from pel­lets may un­der­es­ti­mate the num­ber of soft-bod­ied an­i­mals, like worms and in­sects, the owl has eaten.”

This screech-owl is small (6-10 inches) and quick. It of­ten sits silently on low tree limbs watch­ing for prey or roost­ing there. On sev­eral of my wan­der­ings through forests, I’ve been sur­prised to turn and find my­self star­ing into the eyes of a screech-owl sit­ting on a branch just a few yards away. They al­ways seem un­ruf­fled, usu­ally just blink­ing and star­ing back.

Screech-owls of­ten nest near hu­mans, per­haps hop­ing to pick off small birds at feed­ers, or the ro­dents that come af­ter seed that falls from them, as one was ap­par­ently do­ing on my deck one evening last year. The east­ern scree­chowl’s sense of hear­ing is “so acute that it can even lo­cate mam­mals un­der heavy veg­e­ta­tion or snow,” All About Birds adds.

When I fi­nally got around to open­ing my present, I didn’t find what I’d hoped to find — a com­plete set of ro­dent bones — but rather a mix of tiny bones, bone frag­ments and some other uniden­ti­fied de­tri­tus, per­haps from in­ver­te­brates. Owl pel­lets some­times do have few bones, or none, but I’d love to find one with a com­plete skele­ton to re­assem­ble and, to that end, I keep check­ing out the area where I found the first pel­let.


An east­ern screech-owl lays back its pointed ear tufts, of­fer­ing a less dis­tinc­tive sil­hou­ette.


An east­ern screech-owl snoozes in a tree cav­ity.

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