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Darwin's Eden

Evolving Beaks

Lizards of the Sea

Masked Killers

Paradise Lost?

Viewer Challenge

Letter from Alan Alda

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in the classroom

Voyage to the Galapagos:
"Masked Killers"

Biologist Dave Anderson has been trying to comprehend the baffling realities of masked booby behavior by studying these intriguing Galápagos avian residents for nearly 20 years. Life among the masked boobies of Española has given him unique access to the daily struggles that drive evolution. And, he says, it isn't a pretty sight.

Curriculum Links
National Science Education Standards
Activity: Wild Adaptations



birds, ethology, evolution







(Please visit the Subject-Area Search feature on this website for related Frontiers shows and activities!)


5-8: Structure and Function in Living Systems; Reproduction and Heredity; Regulation and Behavior; Populations and Ecosystems; Diversity and Adaptations of Organisms
9-12: Biological Evolution; Interdependence of Organisms; Behavior of Organisms
5-8: Populations, Resources and Environments
9-12: Population Growth; Natural Resources
Nature of Science/Scientific Knowledge


Biologist Dave Anderson's long-term studies have given him unique insights into masked booby behavior. In masked boobies, the first hatched chick always kills the second, and the parents do nothing to stop it. The practice, called "obligate siblicide," is just one of the harsh realities of booby life on these islands.

Anderson realizes this seemingly cruel behavior is a normal pattern of booby life. And although the behavior may seem counterintuitive in Darwinian terms, Anderson views the behavior as an evolutionary strategy that enables the masked booby to survive as a species.

All living things have evolved adaptations that enable them to survive successfully in their environment. In the isolated archipelago of the Galápagos, plants, reptiles, mammals, birds and insects have had a few million years to evolve adaptations to the unique ecosystem. Here are some examples of Galápagos wildlife, unique to these islands:

  • The 13 finch species in the Galápagos have evolved specialized beak sizes and shapes.

  • Marine iguanas, the world's only seagoing lizards and "lords of the seashore" here, have specialized salt glands to change sea water into potable drinking water.

  • Shells of the subspecies of Galápagos tortoise vary in shape depending on where they live and what they eat.

  • Galápagos penguins have had to adapt to two environments, the hot land and the cool ocean.

  • Over the millennia, other endemic bird species became flightless living here.

Like wildlife on other isolated oceanic islands, wildlife here evolved an amazing diversity and variation. Its isolation also has made it a true living lab for scientists since Darwin's The Origin of the Species was published in 1859.

Take a look at some of the other unique inhabitants of the Galápagos and their adaptations. Consider what the selective advantage might be for their physiology and behavior as you ponder and research these questions:

  • Why does the blue-footed booby have blue feet?

  • Why does one subspecies of giant tortoise have a saddle-backed shell?

  • Why do so many varieties of birds inhabit these islands, but comparably few insects?

  • Why don't penguins fly?

  • Why do sea turtles stay in the water, while tortoises live on land?

  • Obtain samples of different bird foods from supermarkets or pet stores. Choose seeds of varying sizes and shapes. What features do you think would make a bird beak the most effective tool for eating each of the different seeds? Write down a list of helpful features and then design and draw a beak that incorporates those features. Next, find out which birds the seeds are supposed to attract, and see if the beaks you designed match the real bird beaks. Try designing beaks for other functions -- digging grubs out of logs or worms out of the earth.

  • For more details on finch beak design, go to the Destination: Galápagos Islands website, where you'll find sketches of finch beaks, and how they figure into taxonomic keys.

  • Darwin's finches illustrate how one species can diverge and occupy different niches in an ecology. How many different bird species can you find in your environment? Observe birds feeding in your backyard or in a nearby park or aviary. Find examples of different sizes and shapes of bird beaks. Some birds are ground feeders; others will not feed on the ground. Some birds eat seeds; others eat only insects or worms. See if you can determine a relationship between the shape of a bird's beak and what it eats. This activity can also be done by studying illustrations of different birds and comparing their beak shapes and sizes with their preferred food.

You'll find much more information that will help you explore these questions about the wildlife of the Galápagos on the Destination: Galápagos Islands website.

Animals more familiar to us (like cats and dogs) have also evolved adaptations in physiology and behavior that enable them to successfully survive. Practice observation skills on your pets or pets of your friends, and consider such questions as: Why do cats keep themselves so clean? Why don't dogs have sweat glands? Why do dogs prefer human company, while cats are more solitary creatures? What is the advantage to a reptile of being ectothermic? Why don't snakes have eyelids?

Good science begins with observation, and observations of wildlife can be made just about anywhere. Try looking at plants and animals the way an evolutionary biologist would and ask questions: Why do some plant seeds have such thick coatings? Why are roaches, fleas, ticks and other pests so successful? Your questions might be the beginning of a lifelong quest and career! Darwin's real work began when he started asking questions about mysteries of life in the Galápagos.


  1. Design a field guide to the Galápagos that includes photos or drawings of its endemic species. Include both the common and scientific names of the wildlife. Many images can be found online. Add your class studies and projects to your school's website. Or, you might use photos and images to create a scrapbook as though you had been a tourist on these islands. Keep a journal of what you see on the show and find on the Web or through other research.

  2. Choose two or three species, one each from bird, mammal, reptile and plant life, and prepare taxonomic charts that include kingdom, phylum, subphylum, class, order, family, genus, species.


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