NAME Owl Pellet Dissection A Study of Food Chains & Food Webs INTRODUCTION: Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals preyed upon by raptors, or birds of prey. Pellets are produced and regurgitated not only by owls, but by hawks, eagles and other raptors that swallow their prey whole of in small pieces. Owls feed early in the evening and regurgitate a single pellet approximately 20 hours after eating. Predatory mammals such as bobcats and wolves have teeth to grind up bones and claws, and, a digestive tract adapted to pass these ground parts. Owls, on the other hand, do not have teeth for grinding and cannot pass whole bone and claws through their digestive tract safely. The protein enzymes and strong acids that occur in the digestive tract of raptors do not digest the entire meal. The relatively weak stomach muscles of the bird form the undigested fur, bones, feather etc. into a bolus (or wet slimy pellets). Depending upon the prey eaten, the undigested portions may include beaks, claws, scales, or insect exoskeletons. This type of material has little nutritional value and must be passed from the body. In this process even the most fragile bones are usually preserved unbroken. Scientists take advantage of this adaptation by collecting these pellets and examining their contents. Since owls are not very selective feeders, these pellets be used to estimate the diversity of available prey. The contents are also a direct indicator of what an owl has fed on; information that is crucial for species management and protection. The owl pellets that you will be examining in this lab have been collected and fumigated from common barn owls (Tyto alba). Owl pellets themselves are ecosystems, providing food and shelter for communities that may include clothes moths, carpet beetles and fungi. Clothes moth larvae are frequently abundant in pellets, feeding on fur and feathers. The black spheres about the size of periods (.) that are found in the pellets are the droppings of the caterpillars. The larvae metamorphose near the surface of a pellet in cocoons made of fur. MATERIALS: 1 owl pellet (wrapped in aluminum foil) forceps dissecting needle/toothpick dissecting pan/tray several sheets of white paper electronic balance ruler magnifying glass water paper towel latex gloves (pair for each partner)
PROCEDURE: 1) Unwrap and examine the outside of the owl pellet. Describe the external features. Measure and record its length and width in centimeters. Measure and record the owl pellet mass in grams using the electronic balance. Put all data and observations on the Data, Observations, & Analysis page. 2) To investigate the interior of the pellet you must soften it by soaking it in water. Fill your bowl 3/4 full with tap water. Submerge the pellet in the bowl for approximately 30 seconds then remove the pellet and place it in the dissecting tray. 3) Begin picking at the bones, teeth, insect parts, and any other prey evidence out of the fur and place all prey evidence (except skulls) on a piece of white paper. Place the skulls on a second sheet of white paper. Use probes and forceps as necessary, but proceed carefully to avoid crushing any small bones. Discard the fur and other soft matter as you search for bones. 4) Partners that are not dissecting should attempt to identify each of the bones, using Figure 2. Totals should be recorded on the Data, Observations, & Analysis page in the table under question #3. Use the magnifying lens to occasionally identify small bones and separate the occasional litter (i.e. small stone, cartilage, etc.) from the prey matter. The last column in the table is to calculate the percent of the total that the number of each group of bones represents. For example, if there were 5 scapulae out of a total of 55 bones, the % of the total column for scapula would read: 9.09%. Make these calculations once all bones have been identified. 5) Another lab partner should use the dichotomous key below this step and Figure 1 below the key to identify the prey species by skull..(note: You may not always need to locate the mandible (lower jaw) of the skulls to identify the prey specimen. If you have more than one skull, identify each.) Does the animal have... 1. a) 3 or fewer teeth on each side of its upper jaw? b) 4 or more teeth on each side of its upper jaw? 2. a) 2 biting teeth on its upper jaw? b) 4 biting teeth on its upper jaw? 3. a) a skull length of 23 mm or less and brown teeth? b) a skull length of more than 23mm and approx. 44 teeth 4. a) the roof of its mouth extending past the last molar? b) the roof of its mouth not extending past the last molar? 5. a) a skull length of 22 mm or less? b) a skull length of more than 22 mm? 6. a) flat molars? b) rounded molars? Then... go to 2. go to 3. go to 4. it's a rabbit. it's a shrew. it's a mole. go to 5. go to 6. it's a house mouse. it's a rat. it's a meadow vole. it's a deer mouse.
NOTE: Any skull found without teeth AND a prominent ridge of bone forming and eye socket should be identified as a BIRD. Figure 1 (Rodent Skulls): 6) Once all bones have been identified carefully clean each bone as thoroughly as you can. Make sure to remove as much of the debris as possible. 7) The next step will be to recreate at least one of the animals found in your pellet. You will do this by using a piece of white paper, glue and skeletal charts provided. 8) Finish the activity by answering questions #4 & #5 the Data, Observations, & Analysis section. Data, Observations, & Analysis: 1) Qualitative Observations (External Features):
2) Quantitative Data (Descriptive Stats): a. Pellet Mass (g): b. Pellet Length (cm): c. Pellet Width (cm): d. Total Bone Number: Figure 2 (Principal Rodent Anatomy):
3) Bone Tally Table: Bone Tally Number % of Total Bone Tally Number % of Total 4) Discuss how the Bone Tally Table could help a scientist determine the region your owl pellet originated from? 5) Use the information from the table below to draw a Food Web that is representative of your pellet. Prey Mouse Mole Shrew Rat Bird Diet It eats a wide variety of plant and animal matter depending on what is available, including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant products. A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes, millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and millipedes. Shrews also eat small birds, mice, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots, and other vegetable matter are also eaten by some species of shrews. The rat's diet typically includes seeds, nuts, grains, vegetables, fruits, meats and invertebrates. They consume about one-third of their weight in food every 24 hours. Because of their inability to vomit, rats are very hesitant to try new foods that may be poisonous. They will take a small nibble and wait to see if they feel sick and, if so, will avoid that food in the future. insects; terrestrial non-insect arthropods, seeds, grains, and nuts; fruit Draw and label the owl as the top consumer. (Tertiary Consumer) Draw and label all prey found in the pellet as the next level of consumer. (Secondary Consumer) Draw and label any consumers eaten by the prey (use the table above for help). (Primary Consumer) Draw and label any producers eaten by prey or any producers eaten by consumers eaten by prey (use the table above for help). (Producers) Draw energy arrows from victim towards consumer.
From each producer towards each primary consumer that eats that producer. Repeat for each level towards the owl. At the end explain the 10% rule as demonstrated by your food web. OR you can draw an energy pyramid using these organisms to help in your explanation. FOOD WEB