Owl Pellet

Introduction

The heart and core of this scientific paper is to critically examine the owl pellet. In this scientific paper we will overview the common barn owl (Tyto alba), one of nature's most efficient rodent predators, frequently swallows its prey whole. They digest all the fleshy parts of the prey, leaving bones, fur, and chitinous body remains undigested. Such remains are regurgitated (spit-up, to put it bluntly) in the form of a compressed pellet. Pellets are actually formed in the stomach, and are coughed out the beak, usually at the owl's nest or favorite roosting perch. Barn owls typically regurgitate 2-3 pellets per day. By examining recognizable bones and other identifiable remains within a pellet, the barn owl's diet may be determined.

Figure 1. Two sleepy barn owls nearly ready to fledge sit in the rafters of a barn.

Eating Habits of Barn Owls

Barn owls feed primarily on small rodents. These include: rats, mice, moles, voles, gophers, and shrews. They will occasionally feed on somewhat larger prey, such as rabbits or squirrels, but this is less common. Barn owls will also feed on prey other than rodents, such as other birds, bats, lizards, small snakes, large insects, frogs, toads, and very infrequently, fish. Barn owls have voracious appetites and a grown barn owl may routinely devour ½ to its full weight in prey per day when food is abundant. Growing chicks, as seen in Figure 1 below, may even eat more, reportedly up to 1 ½ times their weight in prey per day.

Figure 2. Barn owl chicks 4-5 weeks-old can eat up to 1 ½ times their own weight in prey per day.

Methods and Materials

Collecting pellets

The barn owl pellets that you have received from the South Florida Barn Owl Program were collected from roosting and nesting sites within the Everglades Agricultural Area (EAA). Located just south of Lake Okeechobee, the area is primarily agricultural lands, consisting of sugarcane, vegetables, rice, and sod. Sugarcane is the main crop of this area, supporting abundant rodent populations that live in the fields and on surrounding ditch banks. It has been estimated that rodents cause more than $30 million annually in damage and yield losses to sugarcane alone.

Figure 3. Map of south Florida, showing the 700,000-acre Everglades Agricultural Area south of Lake Okeechobee.

The EAA is a nearly flat, tree-less landscape and there are few natural nesting sites available for barn owls. For this reason, barn owls take readily to nesting in old farm structures (pump houses, pole sheds, storage buildings, abandoned warehouses) and nesting boxes positioned in and around fields. Most of the pellets distributed by ourbarn owl program were collected from these man-made nesting areas. A glance at a barn owl nesting site reveals that they are literally “rodent graveyards, containing tens-of-thousands of rodent bones that have accumulated over the years from regurgitated pellets and uneaten prey.

Figure 4. A barn owl nesting site is literally a rodent graveyard. Note the bones and fur beneath these eggs and days-old chicks at a nest.

Safety during Experiment

The pellets ...