Who Did the Owl Eat?
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WHO DID THE OWL EAT? Overview: Through the dissection of owl pellets, students will learn how owls fit into the salt marsh habitat, which animals live in the owls' habitat (by observing what animals the owls have eaten) and about the skeletal bones of the prey. Content Standards Correlations: Science, p. 292 Grades: K-6 SUPPORTING INFORMATION FOR THIS ACTIVITY Key Concepts: Owls have • Owls are found all over the world. The Barn Owl has 17 specific adaptations that subspecies located throughout the world. enable them to be superb • Owls range in size from 4 '/a inches (least pygmy) to 2 !/2 feet hunters. These adaptations (great grey). include: superb hearing, • An adaptation is a change in a living thing that helps it survive. eyesight, wings, and talons. • Owls have very unique adaptations that make them superb night By studying owl pellets we can hunters. Their facial disks aid hearing - the round area of feathers learn more about the animals that inhabit the salt marsh on the face directs sound to the ears. (Try cupping your hands habitat and about the salt around your ears - it's the same idea!) marsh food chain. • A Bam Owl can hear a mouse chewing grass seeds or moving around 40 feet away. Objectives: • One ear is higher on the head than the other so that the owl can Students will be able to: move their head around too find the exact location of their prey. • define several adaptations of • Since an owl's eyes are found on the front of the head (like owls • identify rodent and bird people) they have binocular vision. bones • Owls eyes are large in order to allow a lot of light to enter. Their • name one thing they can eyes are so big that they have no room to move up, down or learn about the salt marsh sideways. The owl must keep turning its head to follow a moving habitat by studying owl object. Owls have 14 bones in their neck so they can turn their pellets neck 180 degrees each direction. (An owl can turn its neck so far 'and so fast, it sometimes looks as though the head is spinning 360 Materials: degrees!) • Who Did the Owl Eat? Video checked out from the • The feathers on the owl's wing have soft edges that make their Refuge flight silent - another sign of a good hunter. • owl pellets (1 for every • Once the owl has located its prey, it swoops down and grabs it with student or 1 for every 2 its very sharp "claws" or talons. Owls have four talons at the ends students - provided by the of their feathered legs - two face forward and one backward, teachers) while the one the outside can face forward or backward, so they • newspaper or other can have opposing pairs of talons. Once an animal is in the owl's protective covering grasp, it rarely escapes. • quartered Petri dishes or other containers • They swallow their prey head first. • tweezers • The prey goes into the first stomach, a wide place in the • hand Lenses esophagus, where digestion is started. Later it moves down into a • food Web Poster p. 167 second stomach, called the gizzard. All of the meat is digested and • Bone identification chart passed through a tiny opening in the gut. The non-digestible items p. 168 (1 copy for every left in the second stomach are formed into a compact clump of student) bones and fur or feathers (shaped somewhat like egg) which is regurgitated by the owl. This is an owl pellet. Time: 50 minutes Post-Visit Classroom Activities- Birds and Migration Studies 163 • Indigestible animal parts found in pellets include: Ask mammal bones, beaks, claws and bones of birds; ? What is an owl pellet? (Take different bones of reptile and amphibians; hard portions of answers.) insects; and seed husks or other coarse vegetable materials from the stomachs of the prey. Read • Digestion requires 12 to 22 hours. "We are now going to watch video called Who Did • One meal may include a mouse and a bird or two the Owl Eat? to leam more about owls and their owl to three rodents. The marshes around the Don pellets." Edwards San Francisco Bay National Wildlife Refuge have five mouse-sized animals including: Do voles (Microtus califonicus), house mouse (Mus Show the 13 minute video Who Did the Owl Eat? musculus), white-footed deer mouse (Peromyscus maniculatus), salt marsh harvest mouse Ask (Reithrodontomys raviventris), and the wandering ? What do owls eat? (Small mammals and shrew (Sorex vagrans). The red-winged black occasionally small birds.) bird is another important prey item that is ? What is an owl pellet? (Undigested remains of commonly found in owl pellets. what an owl ate. It is the bones, fur and feathers • Owls help keep the rodent population in check. which the owl collects in its stomach and clumps up • Pellets are often associated with birds of prey, into an egg shaped owl pellet, which it then regurgi- however, 330 species of from more than 60 birds tates.) families produce pellets. These families include: ? What does adaptation mean? (A change in a robins, starling, king fishers and tree swallows as living thing that helps it survive.) well as owls, hawks and eagles. ? What types of adaptations would an owl need TEACHING METHOD to be able to hunt at night? (Take many different answers- improved hearing, eyesight, etc.) Preparing for the Activity Do ? Do you think owls are the only type of bird 3 weeks prior to conducting this activity check out the that regurgitates pellets? (No. Pellets are often Who Did the Owl Eat? Video from the Environmen- associated with birds of prey, however, 330 species of tal Education Staff at the Don Edwards San from more than 60 birds families produce pellets. Francisco Bay National Wildlife Refuge (510) 792- These families include: robins, starling, king fishers 0222. and tree swallows as well as owls, hawks and eagles.) Conducting the Activity Do Read Cover the students desks or work tables with "Scientists dissect owl pellets to look a the different newspaper or other protective covering. bones, fur, or feathers that are inside." Read Ask "Owls are found all around the world. They range in ? As scientists, what can we learn from owl size from 4 !/2 inches (least pygmy) to 2 Vi feet (great pellets? (A scientist might want to study owl pellets grey) long. There are a few different types of owls to learn how owls fit into the food web, to find what found throughout the San Francisco Bay including, animals live in the owls habitat, and to learn about the burrowing owls, short eared owls, and barn owls. skeletal bones of their prey.) Today, we are going to be studying owls by dissecting owl pellets." Read "Today we are going to become scientists to find out what species of animals these owls have eaten." 164 Post Visit Classroom Activities- Birds and Migration Studies Do premolars, unlike the deer mouse (above). Pull a Pass out the owl pellets (1 per student or 1 to a pair molar and note the roots on the tooth. of student), the quartered petri dishes or other containers, tweezers, and hand lenses. Salt marsh harvest mouse: You may never see one of • Have the students break the pellets apart by these (they hide very well and are not easily captured grasping each end and then slowly and gently by owls; in addition they are not found in owl pellets pulling the ends apart. from geographic areas outside of the San Francisco • Continue to pull mats of fur or feathers apart Bay), but if you do, remember that the upper incisors looking for skulls and bones. (Tweezers are (front teeth) are orange and have a vertical groove in available for removing stubborn fur.) each tooth. • The bones from each pellet can be separated by type in the quartered petri dish. Roof rat: These are larger than any of the rodents listed above. The teeth have roots, but not on the • Give each student a copy of the bone identification mount of sample skulls that the parietal bone in the chart on p. 168. Have the students place the rear part of the skull is shaped differently between bones in the appropriate places on the chart. the roof rat and Norwegian rat. Holding the skull • Circulate around to the students and help them facing away from you, note that the parietal of the identify the bones. Bones found in pellets can be roof is wider and more narrow, like the roof of a from rodents, shrews, and birds. Note: The salt house. Whereas, the parietal of the Norwegian rat is marsh harvest mouse is found in the salt higher in relation to width. marshes of the San Francisco Bay, but will not seen in pellets that are ordered since they come Norwegian rat: See above. A parietal bone is wider from a different geographic location. If you than that of the Roof rat. This rat also has roots on have owl pellets from the San Francisco Bay the molars. Area they still probably will not be seen because this mouse stays under cover and can Gopher: The skull is much larger than that of the rat not ordinarily be caught by an owl. or mouse, with sturdy molars that have no roots. Identification of Some Common Prey Types Order Insectivora are small mammals that eat Order Rodentia consists of small to medium sized insects. These include shrews, moles, and bats. mammals, including squirrels, marmots, mice, and Below is a list of mammals from order Insectivora rats.