Method: Students examine owl pellets, reconstruct prey skeletons, and draw a food chain based on the contents. 方法：学生观察猫头鹰粪便，重建猎物骨骼，并根据内容绘制食物链。
Materials: Owl pellets (see information in the “Background” section), dissecting tools such as toothpicks or tweezers, one copy per group of the Owl Pellet Data Sheet, paper plates (one per student), reference materials. OPTIONAL: magnifying lens, gloves, cardstock, glue. 材料：猫头鹰粪便（参见“背景”部分的信息），解剖工具如牙签或镊子，每组一份猫头鹰粪便数据表，每个学生一个纸盘，参考资料。可选：放大镜，手套，卡纸，胶水。
Activity Time: one 30- to 60-minute session 活动时间：一次 30 至 60 分钟的课程
People Power: groups of two or three students 人力：两人或三人的小组
The Ecosystem Concept and Project WILD, Field Ethics, Using Local Resources 生态系统概念与 WILD 项目，田野伦理，利用地方资源
Unlocking the secrets of a food chain.... 揭开食物链的秘密……
Objectives 目标
Students will (1) analyze owl pellets and reconstruct skeletons of prey animals; (2) construct a simple food chain; and (3) identify the trophic levels associated with the organisms in the food chain. 学生将（1）分析鹰粪并重建猎物动物的骨骼；（2）构建一个简单的食物链；（3）识别食物链中生物所属的生态位。
Background 背景
It is late spring and you are a female barn owl. You have been courted by your mate, found a suitable nest site, and have laid six eggs. The conditions are good this year, and you went into breeding season at a healthy weight. Because of this, all six of your eggs have hatched. Now the real work starts. Immediately upon hatching, your young chicks are hungry. Between you and your mate, you must catch four mice per chick every night. That amounts to 24 mice every night, not including the six mice you and your mate each need to survive. So, between you, your mate, and your young, your family will need 36 mice-every day! Just imagine: this same scene is carried out in barns, abandoned buildings, and roosting sites across the world. A large number of mice and other prey are required to sustain these owl families. 现在是晚春，你是一只雌性草鸮。你的伴侣已经向你求偶，你找到了一个合适的巢穴，并产下了六个蛋。今年的条件很好，你以健康的体重进入了繁殖季节。因此，你的六个蛋都孵化了。现在真正的工作开始了。刚孵化时，你的幼雏们就饿了。你和你的伴侣必须每晚为每只幼雏捕捉四只老鼠。这意味着每晚需要捕捉 24 只老鼠，还不包括你和你的伴侣各自需要生存的六只老鼠。所以，你和你的伴侣以及你的幼雏们，你的家庭每天需要 36 只老鼠！想象一下：这个相同的场景在世界各地的谷仓、废弃建筑和栖息地中上演。维持这些鸮的家庭需要大量的老鼠和其他猎物。
This idea can be easily illustrated with a trophic level pyramid. The pyramid, sometimes referred to as an energy or biomass pyramid, shows the producers at the bottom, largest level. This level consists of plants and all organisms that create their own food, most of which use the sun’s energy through photosynthesis. The next, smaller level represents the primary consumers-those animals which eat the producers. The third, even smaller level represents the secondary consumers-those animals which eat either the primary consumers or the primary consumers and producers. And, finally, the top, smallest level represents the tertiary consumers-those animals which are top predators and eat the primary and secondary consumers. 这个概念可以用营养级金字塔轻松说明。这个金字塔有时被称为能量金字塔或生物量金字塔，底部是最大的层级，显示的是生产者。这个层级由植物和所有能自己制造食物的生物组成，其中大部分通过光合作用利用太阳能。下一个较小的层级代表初级消费者——那些吃生产者的动物。第三个更小的层级代表次级消费者——那些吃初级消费者或初级消费者和生产者的动物。最后，最顶层、最小的层级代表三级消费者——那些是顶级捕食者并吃初级和次级消费者的动物。
For the barn owl in our example to have enough mice to eat, the population at the primary consumer level (mice) needs to be much larger than the population at the tertiary consumer level (owl). Similarly, for the mice to have enough food, the producer 为了使我们的例子中的猫头鹰有足够的田鼠吃，初级消费者层级（田鼠）的种群需要比三级消费者层级（猫头鹰）的种群大得多。同样，为了让田鼠有足够的食物，生产者
level must contain the greatest number of organisms of all the levels. Thus, the amount of energy and biomass is greatest at the lowest level, decreasing incrementally with each higher level. If the diagram were a cube rather than a pyramid, the organisms at top levels would eventually run out of food. 每个层级必须包含所有层级中数量最多的生物。因此，能量和生物量在最低层级最大，随着层级的升高而逐级减少。如果这个图示是一个立方体而不是金字塔，那么顶层生物最终会耗尽食物。
North America is home to 19 species of owls. All owls are carnivores, but their preferred prey depends on size. Smaller owls such as screech owls will eat insects and small rodents. Larger owls like the barred owl will eat larger rodents and rabbits. The largest owls such as the great horned owl will eat large rodents and mediumsized mammals such as skunks. When an owl captures is prey, it usually consumes the entire animal-the head, tail, brains, intestines, bones, and even fur. However, the owl is only able to digest certain parts of the prey animal. The soft tissue, including the muscles, organs, and skin, provides nutrients to the owl and is passed through the digestive system. The bones and fur or feathers, however, cannot be digested by the owl. These indigestible parts go into the owl’s gizzard, a muscular pouch located between the neck and intestines. A few hours after an owl eats its meal, the bones and fur are compacted by the gizzard into a pellet. Before the owl eats again, it will regurgitate (cast) the pellet. (NOTE: Owls do not vomit the pellet; they simply lean forward, flex their muscles, and cast the pellet.) Owls are not the only birds that cast pellets. More than 300 species of birds cast pellets-from large eagles and hawks to smaller birds like robins and tree sparrows. 北美洲有 19 种猫头鹰。所有猫头鹰都是肉食性动物，但它们偏好的猎物取决于体型。较小的猫头鹰，如夜鹰，会吃昆虫和小型啮齿动物。较大的猫头鹰，如条纹猫头鹰，会吃较大的啮齿动物和兔子。最大的猫头鹰，如大角猫头鹰，会吃大型啮齿动物和中型哺乳动物，如臭鼬。当猫头鹰捕获猎物时，它通常会吃掉整个动物——包括头、尾巴、大脑、内脏、骨头，甚至毛皮。然而，猫头鹰只能消化猎物动物的一部分。柔软的组织，包括肌肉、器官和皮肤，为猫头鹰提供营养，并通过消化系统排出。骨头和毛皮或羽毛，但猫头鹰无法消化。这些无法消化的部分进入猫头鹰的砂囊，这是一个位于颈部和肠道之间的肌肉囊。猫头鹰进食几小时后，砂囊会将骨头和毛皮压实成一个小球。在猫头鹰再次进食之前，它会反胃（吐出）这个小球。（注：猫头鹰不会呕吐小球；它们只需向前倾斜，收缩肌肉，并吐出小球。）不是只有猫头鹰会吐出小球。 超过 300 种鸟类会吐出粪便——从大型鹰隼到像知更鸟和树雀这样的小型鸟类。
Owl pellets are clean of all flesh and virtually odorless. Once the bones are separated from the fur, they can be readily identified. Owl pellets have been used for scientific study of small mammals and their distribution. With owls doing the collecting, the scientist must simply locate the owl roost to obtain skulls and bones of the small prey living in the area. From those parts, the prey species can be identified. 猫头鹰粪便不含任何肉，几乎无味。一旦将骨头从毛皮中分离出来，它们就可以被轻易识别。猫头鹰粪便已被用于科学研究中小型哺乳动物及其分布情况。由于猫头鹰负责收集，科学家只需找到猫头鹰的巢穴，就能获取该地区小型猎物的头骨和骨头。从这些部分中，可以识别出猎物种类。
Owl pellets help map the areas occupied by certain small creatures that might otherwise have escaped detection. Scientists can then estimate the rodent population in an area and use the data to better understand the availability of habitat components in an ecosystem. 猫头鹰粪便有助于绘制某些小型生物占据的区域，这些生物可能原本难以被发现。科学家们可以据此估算某一地区的啮齿动物种群数量，并利用这些数据更好地理解生态系统中栖息地组成成分的可用性。
NOTE: To complete this activity, educators will need to purchase owl pellets from a scientific supply company or distributor (e.g. pellet.com, pelletsinc.com, pelletlab.com, carolina.com, acornnaturalists.com). These pellets are heat-sanitized and are safe to use with students. 注意：要完成此活动，教育工作者需要从科学供应公司或分销商处购买猫头鹰粪便（例如 pellet.com、pelletsinc.com、pelletlab.com、carolina.com、acornnaturalists.com）。这些粪便经过热消毒，可以安全地用于学生。
Read the first paragraph of the “Background” section aloud to students, and describe how owl pellets are formed. Explain to students that they will be dissecting owl pellets to investigate what owls eat. After identifying the prey in the pellets, students will then find out what those prey animals eat and construct a food chain. Visit www.projectwild.org for a video link of an owl casting a pellet. 向学生朗读“背景”部分的第一段，并描述猫头鹰粪便的形成过程。向学生解释他们将解剖猫头鹰粪便，以调查猫头鹰吃什么。在识别粪便中的猎物后，学生将找出这些猎物动物吃什么，并构建食物链。访问 www.projectwild.org 获取猫头鹰排出粪便的视频链接。
Divide students into groups of two or three. Review safe lab procedures, including the need to wash hands after doing the activity and the importance of not eating or drinking during the activity. Give each team an owl pellet, tools for dissection, and an Owl Pellet Data Sheet. Give each student a paper plate to serve as his or her workspace. 将学生分成两人或三人的小组。复习安全实验室程序，包括活动结束后需要洗手以及活动期间不能吃东西或喝水的注意事项。给每个小组一个猫头鹰粪便、解剖工具和一份猫头鹰粪便数据表。给每个学生一个纸盘作为其工作区域。
Have the groups carefully divide the owl pellet into two or three segments depending on the number of students in the group. Next, inform the students that their job is to separate the bones from the fur and feathers. Remind students to keep their owl pellets, the bones, and the fur or feathers on the paper plate to ease cleanup. Where possible, identify the skulls, jaws, and all bones of the prey species. Use the bone chart on the Owl Pellet Data Sheet as a guide. (Some pellet providers may also include a bone chart with the pellets.) Consider using a hand lens or magnifying glass to look at the teeth. Look at the shape of the teeth and how they are arranged. Would the prey’s teeth work best at tearing flesh, grinding seeds, or eating plants? Using the teeth as a guide, indicate what kinds of food the prey species most likely ate. Consult Internet or library resources to find out the animal’s typical diet. 让各小组仔细将猫头鹰粪分成两到三段，具体数量取决于组内学生人数。接下来，告知学生他们的任务是分离骨头和毛羽。提醒学生将猫头鹰粪、骨头以及毛羽放在纸盘上，以便于清理。尽可能识别猎物的头骨、颚骨和所有骨头。使用猫头鹰粪数据表上的骨骼图作为参考。（有些猫头鹰粪提供者可能会随猫头鹰粪附赠骨骼图。）考虑使用放大镜或手持放大镜观察牙齿。观察牙齿的形状以及它们的排列方式。猎物的牙齿最适合撕裂肉、磨碎种子还是食用植物？根据牙齿的特征，推断猎物最可能食用的食物种类。查阅互联网或图书馆资源，了解该动物的典型食谱。
Ask students to determine if there are bones from more than one animal in the pellet. If there are, determine how many different animals and species are represented in one pellet. Have students record their data on the Owl Pellet-Data Sheet. 请学生判断猫头鹰粪中是否含有多种动物的骨头。如果有，确定一个猫头鹰粪中代表了多少种不同的动物和物种。让学生将他们的数据记录在猫头鹰粪数据表上。
Instruct students to lay out the bones to form as many complete skeletons as possible. Skeletons may be glued to card stock paper for display and labeling. 指导学生摆放骨头，尽可能多地组成完整的骨骼。骨骼可以粘在卡纸板上进行展示和标注。
From the evidence suggested by the skeletons, discuss a variety of possible food chains that include the owl, its prey, and what the prey eats. The owl pellets reveal what the owl has consumed; what might consume the owl pellets? (Decomposers and detritivores.) 根据骨骼提供的证据，讨论包含猫头鹰、其猎物以及猎物所吃的食物的各种可能的食物链。猫头鹰的粪便揭示了猫头鹰所吃的食物；什么可能会吃猫头鹰的粪便？（分解者和食碎屑动物。）
Have a classroom discussion about trophic levels. Identify where producers, primary consumers, secondary consumers, and tertiary consumers fall on the pyramid. Explain to students that organisms at each level obtain energy from organisms at lower 在课堂上讨论营养级。确定生产者、初级消费者、次级消费者和三级消费者在金字塔中的位置。向学生解释，每个级别的生物都从较低级别的生物那里获取能量。
