One Species at a Time Podcast: 5:30
1) Listening Guide
Biologists studying killer whales face the challenge of studying organisms that spend the majority of their time underwater. This story and accompanying materials and lessons explore the difficulty of studying killer whales and emphasizes the reasons that scientists are willing to work so hard to study them. In addition, the story discusses adaptations that different populations of killer whales have evolved to capture prey.
2) Listening Prompts for Students
a. Why do the researchers enjoy studying killer whales?
b. Where do killer whales live? Why does that it make it difficult for biologists to study killer whales?
c. What do killer whales eat? Are there differences in the diets of killer whales living in different places?
d. How does the feeding behavior of killer whales feeding on fish differ from that of killer whales feeding on seals and porpoises? What is the reason for that difference?
e. How do the researchers in the podcast locate dolphins in order to study them?
f. Do you think you have the patience required to be a killer whale biologist?
3) Play the One Species at a Time Story
4) Reading Guide
Killer whales, orcas, are the largest member of the dolphin family. They are highly social animals that live in groups and rely on heavily on sound to locate their prey and communicate with other killer whales. Killer whales eat a wide range of prey and use different strategies to capture different types of prey.
5) Reading Prompts for Students
a. What do scientists call a group of killer whales? How many individuals typically live in a group?
b. What types of sounds, or vocalizations, do killer whales use? What is the purpose of each type of call?
c. What types of food do killer whales eat? What is a hunting strategy that killer whales use to capture fish? What is a hunting strategy used by killer whales to capture marine mammals?
d. How does the pod size vary between killer whales hunting for fish and killer whales hunting for marine mammals?
6) Read the Encyclopedia of Earth Article (focus on the sections on Behavior and Food habits)
7) Watch Video (38 sec)
Nothern Resident Orca vocalizations.WWF Canada.
Total lesson time: 90 minutes
Listening time: 5:30
1. What would it be like being a biologist that studies killer whales?
Put students in small groups of 2 – 3. Have each group discuss the good aspects and bad aspects of studying killer whales. Have each group come up with a list of three good things and three bad things about studying killer whales. Have each student write a paragraph answering the question- “Would you like to study killer whales? Why or why not?”
2. How do killer whales capture their food?
Killer whales are social hunters (hunt in groups) and their hunting strategy varies depending on the type of food they are eating.
Have students discuss how killer whales use vocalizations to capture their prey. What is the purpose of “clicks”? What is the purpose of making other calls when hunting prey? Why would killer whales feeding on fish benefit from using clicks, calls, and whistles? Why wouldn’t killer whales feeding on dolphins and whales make sounds while hunting? What other senses could killer whales feeding on seals and dolphins rely on? Discuss other adaptations killer whales have to catch food. Have students write a paragraph discussing feeding adaptations of killer whales.
Have students discuss the costs and benefits of hunting in groups. What are some examples of animals that hunt in groups and what are examples of animals that hunt alone? Discuss reasons these differences in hunting strategy. How can killer whales benefit from feeding in groups? Why might killer whales choose to feed in different sizes of groups when feeding on different types of prey?
Researchers studying killer whales around Vancouver Island in British Columbia, Canada have observed that transient pods may break up into smaller groups while hunting marine mammals. When they discovered a group of killer whales, scientists followed them for as long as they could and documented the number of times that the killer whales successfully captured food. Note: the scientists were unable to spend the same amount of time observing pods of different sizes.
This data was taken from the article “Ecological and social determinants of group size in transient killer whales”. By Robin W. Baird and Lawrence M. Dill. Published in Behavioral Ecology Volume 7, pages 408-416. http://www.cascadiaresearch.org/robin/BehavEco.pdf
Group Size Time Observed (hours) Observed Number of Successful Prey Captures
1 31.9 2
2 41.9 12
3 111.4 53
4 65.8 15
5 51.6 9
6 42.4 18
8 15.6 3
9 13.2 0
Looking at the Data
1. Draw the graph that shows how the length of time scientists spent observing a group varied with pod size. (hint: think about what type of graph is most appropriate to display this information)
Graph Interpretation Question: What pod size was observed for the longest period of time?
Biology Question: If pods of different sizes were equally successful at catching prey, then which pod size should have been observed to catch the most prey? Why?
2. Draw the graph that shows how the number of successful feeding attempts depended on pod size?
Graph Interpretation Question: Which pod size had the most successful captures?
Biology Question: What are two possible reasons that scientists observed pods with three members capturing food more than any other pod size? Think about how to distinguish between these two possibilities.
Hint: If killer whales are equally effective at capturing prey regardless of the size of the hunting group then we might expect to observe the most captures by the group size that we had observed the longest. To determine which group size is best for catching prey then we would have to figure out which groups caught prey at the highest rate (that is, the number of successful captures/time observed).
3. Calculate the rate of successful captures per foraging time by dividing # captures by the observation time. Draw the graph that shows how the rate of successful captures depends on pod size.
Graph Interpretation Question: What size of pods had the highest rate of successful food capture?
Biology Question: The capture rate of pods with 3 and 6 members were very similar. Do you think that it matters to the dolphin whether they are feeding in a pod of 3 or 6 members? Which pod size do you think would be best? Why? How would you try to test your ideas?
4. Using a fairly complicated formula, the scientists estimated the average amount of energy gained per day (measured as Kcal/kg/day) by killer whales feeding in groups of different sizes.
Group Size Average Energy Intake
(# ind) (Kcal/kg/day)
Draw the graph that shows how average energy intake depended on pod size?
Graph Interpretation Question: Which pod size had the highest average energy intake?
Biology Question: Which is the best group size for hunting marine mammals in this environment? Write one paragraph discussing your answer.