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PACIFIC LIFE WHALE EDUCATION KIT - LESSON 5
Echolocation and the Web of Life
Goals/Objectives:
Students will:
- Learn about echolocation and how whales use it to find food.
- Discover how important the web of life is to each member of the food chain.
Teacher Overview:
Students engage in activities that demonstrate two of the many adaptations whales have for hunting. They will also participate in a demonstration of the delicate balances between species that exist in ocean ecosystems.
Time: 45-50 minutes
Setting: Indoors and Outdoors
Subject: Science, Visual Arts
Key Words: Bubble-net feeding, Food web, Diatoms, Primary Producers, Zooplankton
Background information:
In Lesson Four we explained how whales utilize echolocation to hunt and locate prey, to choose the right direction in which to find a companion and to navigate their way across the open seas. Just as a ship steaming through a fog-covered sea uses radar to see other ships and islands through the mist, whales use sound and their extremely acute sense of hearing to see the ocean world beyond their narrow field of vision. Based on the returning echoes whales receive from the sounds they create, they can tell many things about their surroundings and about objects both near and far. One of the basic pieces of information that can be obtained using echolocation is the position of an object relative to the echolocator. The Whale-Shrimp activity in this lesson will help illustrate this idea.
Obtaining enough food and water is necessary for all life. Many of the adaptations we have learned are related to locating and catching food. Whales have unique food-related adaptations such as echolocation to locate prey, baleen and teeth to catch it and blubber to use as fuel for getting through periods of starvation between long periods of fasting.
A fascinating and unexpected strategy for catching fish is employed by humpback whales (a type of baleen whale).The behavior is called cooperative bubble-net feeding. and only occurs in one location - Alaska. A group of whales start by forming a circle. The whales submerge and simultaneously create a ring of bubbles while swimming in a circle. One of them shrieks an eerie sound (Individual whales and even larger groups also employ this technique.) The fish move close together and will not cross the bubbles net. The rising bubbles literally act as a corral to contain the fish. The whales, now positioned on their sides in a vertical position, move up through the middle of the bubble-net and surface with their mouths wide open, taking in huge gulps of fish-filled water. Almost in unison, the entire group of whales come up in a synchronized upward lunge. The whales almost appear to be playing positions on a coordinated team.
With such complicated strategies for finding food and communicating with one another to synchronize themselves, the natural question is, are whales intelligent? It is hard to know what constitutes intelligence in an animal like a whale that is so different from a human. There are factors that point to it, but inconclusively things such as the size and formation of the brain, complex social behaviors and the practice of what seems to be unselfish concern for the welfare of others in their pod and even other species. These seem to be indicators of greater intelligence than animals lacking such features.
Whales have large, highly structured brains. The sperm whale has the largest brain of any animal, weighing in at around 20 pounds! Whales also live in complex social systems (though we still have a lot to learn about the social systems of baleen whales). Mothers and calves form long-lasting bonds during which the calf must learn important strategies for coping. Whales also appear to display emotions such as grief when a companion dies. They may stop eating and/or withdraw from social activities.
There is also evidence that whales use sound to communicate. Sperm whales make strings of distinct clicks, called codas, that may contain important information. In addition to their echolocating chirps, dolphins may use signature whistles the way we use names to recognize each other. Humpback whales compose rhythmic songs that they change. They learn from each other. Perhaps the most impressive indication of intelligence is when whales help each other unselfishly.
All of earth's creatures, including plants, rely on the delicate balance of nature to provide a secure habitat for growth, nutrition and survival. As the planet is mostly covered by water, it is critical that we learn to preserve aquatic ecosystems.
The food web or food chain is one way of demonstrating how each group of plants and animals are interconnected. Imagine a pyramid; at the bottom you have plants and the smallest of creatures, the primary producers in the ocean, which are called diatoms (microscopic algae). (Primary producers are the basis of the food chain and supply hundreds of millions of tons of food to animals.) The pyramid ascends with larger and larger kinds of zooplankton creatures. These provide tens of millions of tons of food to the larger animals above them such as fish and squid. At the top of the pyramid eating fish and squid, are toothed whales, like dolphins, as well as birds and even humans! There is a higher level that includes a few orcas and large sharks which sometimes eat dolphins and seals. About two-thirds of the way up this pyramid is krill. Feeding on the krill are seals, penguins, other bird species, some fish species and baleen whales. (For more information, read Southern Ocean Food Web, The Natural History of Whales and Dolphins, Evans, P., Facts on File, Inc. New York, 1987, pp. 246.)
All levels of every food pyramid require that each level remain intact to support the level above. This means if you remove the zooplankton you starve the krill, which will mean no food for larger animals. If you remove squid, there might not be enough other types of food for squid-eating sperm whales. If you remove all the fish, there will be an overabundance of plankton, yet not enough food for birds, seals, whales and yes, for us seafood-loving humans.
In many ways nature can take care of itself, as seen in habitat recoveries after oil spills and natural disasters. Humans have introduced chemicals such as dioxins (substances found in hundreds of synthetic products) into the environment. When the chemicals get into the oceans and the food pyramids, the organisms in which they end up have no way to get rid of them. These chemicals interfere with normal reproduction and development. Strict measures must be put in place to stop dangerous chemicals from getting into the oceans. The responsibility to care for the delicate balance of life on earth will soon be in the hands of today's students. It is today's ecologically responsible teacher who will empower them to understand and accept this responsibility and to act upon it.
The Web of Life Activity at the end of this lesson will show your students the importance of this concept and will give students a sense of the fragile ecological balance of nature. Lesson Six will offer solutions and actions that help take care of the environment.
Materials:
- 4 Blindfolds
- Small ball of yarn or string
Before Class:
- Have yarn and blindfolds ready.
During Class:
This activity demonstrates how some whales use echolocation to locate and capture their food. It can be played in a large open room or outside. If you have a large class, you may want to break into two groups.
Whale-Shrimp Activity:
Have your class form a circle. The circle represents the ocean boundaries and is responsible for keeping all ocean life in the circle during this activity.
Choose two students and blindfold them in the middle. Put four or five other students in the center and give them names like rock, seaweed, boat, surface and sea floor.
One student is the whale and the other is a shrimp. The whale calls in a deep voice, "whale," and the shrimp must answer in its tiniest, highest voice, "shrimp." (This is played like Marco Polo, but out of water.)
The students forming the ocean boundary circle put their hands up, palms inward, to stop the whale and shrimp from going out of the circle if necessary. They should not push.
The students in the circle with names other than shrimp also call out every time the whale calls out but they should all call back in the same or softer tones than the whale is using.
The whale tries to tag the shrimp. When tagged, two more students come into the center to be blindfolded and become the whale and shrimp.
Discuss:
- How is this similar to the way toothed whales find their food? (Echoes come from many things in their environment, not just food. Whales must pick out different types of objects without being able to see them.)
- How is it different? (Whales receive MANY more echoes back at one time, plus all of the noise in the ocean, wind, waves, other animals, boats, geologic sounds, surf and much more. They can filter through all of this extraneous sound to 'see' their prey in enough detail to catch it.)
- Do you think that when whales are echolocating they send out a few sounds or lots? (Whales continually send out sounds into their surroundings, just the way humans spend their waking hours with their eyes open.)
One of the reasons scientists are so interested in studying whales is that whales possess what appear to be especially complex brains. The question of whether whales are intelligent in the same sense that we apply that word to ourselves has been the subject of much discussion. In spite of our efforts we still have no real idea of what it is that whales do with their complex brains.
We assume whales are intelligent. They often display behavior which is hard to call anything but elaborate play (including holding their tails aloft to catch a breeze and sailing downwind).They sing complex songs which they continually change (a thing that is very rare among animal singers).These songs sometimes contain rhyme (unique to humpback whales). Some toothed whales support and help dying comrades to breathe. They sometimes push drowning human swimmers towards shore (we would of course, never hear from a drowning swimmer that got pushed away from shore).They cooperate to catch whole schools of fish by creating nets made of bubbles, then rising en masse in a consistent, fixed formation inside the bubble net up through the huddled school of fish so that fish which escape the open mouth of one whale get caught by the whale trailing just behind and on its flank. All of these things point to a brain that may be capable of sophisticated things such as strategizing or generalizing, even of recognizing problems and solving them.
The big question is whether whales are capable of language. Everyone seems to hope that we will soon be able to chat with a whale about its world. Even though it has been demonstrated that whales can handle simple sentences with subjects, verbs and objects, the kinds of interactions we long to have with them has escaped us. We have just begun to be able to demonstrate that whales communicate by any but the simplest and most obvious means. In this sense, we know far more about the language of dancing bees than we do about whales. It is quite possible that whales use their large brains for sophisticated forms of acoustic processing so they can coax more information out of the echoes that are returning from the things around them. A whale might from a single sound in a dark ocean, determine the contours of the bottom, the fish that are swimming by and the other predators that are awaiting their turn to catch those fish. However, this is guesswork and though we know something about the ways that whales echolocate, we must be content with the thought that they represent an intelligence on earth that is not like ours, but perhaps just as advanced. Perhaps one of the children in your class may someday provide answers to the question of what whales are doing with their enormous brains.
Activity: Web of Life
- Have students form a circle and explain that they are going to be creating a food web.
- Select a student to begin the food web. Take a ball of string and hand the start of the ball to the first person. Unravel the ball, handing an equal portion to each successive student until all students form a web, interconnected with the string.
- Ask the first student to name the first level of the food web starting with producers (plants). (See Food Web Diagram for more information.) Explain to the students that the producers, at the start of the web, are in turn eaten by another animal higher up on the food chain and so on until the top is reached. i.e.,orca or great white shark.
- Repeat the question of naming something in the food web from the ocean that might have a relationship or connection with the previous answer.
- While the student continue to hold the web, ask the students if any parts of the circle are more important than any other parts?
- If something happens to one part of the web, how does it effect the web as a whole? What if large amounts of krill were killed due to a chemical or oil spill? In real life, they would be affected by the die-off of krill.
- Go to one person in the web and give the string a gentle twang. How many students could felt it? Have each student who felt the twang gently pull on his or her segment of string. When a student feels a gentle tug, have them give a gentle tug in return.
This example of a food web represents the interconnection of all creatures.
- Is there any part of the web that doesn't eventually feel the effects of the krill die-off?
- Should humans be represented in the web? Why or why not?
- What sort of benefits to humans might we reap with the study of whales?
Think of a spider web. The spider sits in the middle of the web waiting for prey to come along. It takes only the slightest touch of any part of the web to alert the spider to prey or an intruder. Where might humans be in a web like this? Might we be able to perceive problems in our living world by paying attention to this web of life?
Extension Idea:
Have students illustrate an ocean food chain starting with marine plants, moving up through herbivores, carnivores, and top carnivores. Challenge them to see how long they can make their food chain. The longest food chains on earth are in the ocean.
Teacher Wrap Up:
As we've learned, whales possess high level abilities to communicate with each other and assess their surroundings. Discovering these traits in whales, scientists are led to believe that these animals also possess an intelligence not like ours but perhaps more complex.
When we think of reasons to study and protect whales, one of the most compelling is to understand this intelligence in the ocean.
When we stretched the Web of Life across this classroom we saw a model for the larger cycles that bring our planet to life. The most important idea to take from this activity is a sense of how fragile the balance of life is and how the decisions we make everyday can pull the cords of this web.
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