Chapter 1: Animal Communication

1. Name three scientific fields that are helpful to our studies of animal communication. What tools and perspectives do they lend to these studies.

2. Is communication necessary for animal reproduction? Why or why not? 3. Animal communication is referred to as a multi-dimensional transfer of information from

a sender to a receiver. Name three sensory modalities and how a particular animal could use them to transfer information?

4. What are the two requirements of “true” communication? How do these requirements provide testable hypotheses for how selection shapes communication?

5. Male sage grouse (book cover) and male cardinals have some similarities and some differences in their display. Likely you have seen and heard male cardinals searching for mates. I showed a video of the male sage grouse display on the first day of class. What are the benefits and what are the costs to each of these displays. In your opinion, which is more costly?

Chapter 2: Sound

1. What is the difference between refraction and reflection? How are sound waves altered as they pass through different media with varying acoustic impedances?

2. How does impedance affect sound production and reception in air versus in water? 3. What is a decibel and what does it measure? How do decibels vary as pressure or sound

intensity is increased by a factor of 10 or a factor of 100? 4. Puffins are sea birds that can fly and swim. They also build their nests inside burrows

that are 2-3 feet long. Let’s say a puffin squawks at 378 Hz. What is the wavelength of their sound wave in the air, water, and the ground where their nests are?

5. Assume a puffin made that squawk in either air, water, or next to the ground. In which of the three substances would the sound travel the farthest? Why?

6. Imagine an organism living on the fictional planet Densor. Planet Densor has a very dense atmosphere, about 0.5 g/cm3, but the speed of sound in this atmosphere is 2.9x104 cm/s. In contrast, on Earth the air’s density is 0.00118 g/cm3, and the speed of sound is 3.4x104 cm/s. How would sound impedance differ on Densor vs on Earth? Show your calculation.

7. A common beetle of the genus Hemicoelus, also known as the death watch beetle, emits a characteristic clicking sound which was once believed by superstitious people to signify an oncoming death. This beetle is generally about 2.5-5mm in length. If the sound wave emitted by this beetle is about 85 Hz and the speed of sound is 340 m/s, what type of scattering is occurring relative to the beetle when makes its sound and what are the characteristics of this scattering?

Chapter 3 and 4: Sound production

1. Define nodes and antinodes and explain how they relate to sinusoidal waves using a graph.

2. What does a sonogram tell us? What plot is often shown with a sonogram and what information does it provide?

3. When two notes on a spectrum overlap in time, and are not harmonically related, what does this tell you about the animal that produced the sounds? What is an example of an animal capable of producing such sounds?

4. Think about what you know about how a frog produces sound. What technique(s) do they use to produce vibration? What role does an air sac (as pictured) play in the production of vibrations?

5. A grasshopper has 30 bumps raised in a line on its body. Its leg can rub against them to make a sound. (a.) If the leg can move 60 times in a minute, what frequency will be produced by this animal? (b.) Without the stridulation, how fast would the leg have to move in a minute?

6. Why is it difficult for aquatic animals to use resonators and how do fish circumnavigate this limitation?

7. Why do animals use horns in producing sound? Chapter 5: Sound propagation

1. What are the 3 types of scattering for sound? Describe the relationship between the size of the object and wavelength for each, as well as how the sound is scattered.

2. What is spreading loss? If the distance increases by a factor of 4 what is the spreading loss in dB? How does it differ in air and in water?

3. A bird in a tree wants to communicate with a bird on a roof. Its signal will propagate in at least two ways: directly and through a reflected wave. Depending on the reflection coefficient, R, there can be a phase shift at the boundary and the resulting reflected wave will interfere with the direct wave. With R>0, there will be no phase shift. With an R<0, there will be a 180° phase shift. Draw a picture of one scenario and explain whether destructive interference will occur based on some hypothetical path lengths and a particular sound wavelength.

4. Think about sound refraction for marine versus terrestrial organisms. What are the optimal times of day or of the year for terrestrial and marine animals to communicate over long distances?

5. A baby elephant on the savanna has been separated from its family by a sudden wildfire that broke out during the night. It tries to call to its mother directly on the other side of the fire but she does not respond (though she is alive). His calls are answered by relatives further away, behind him. Sketch a graph of why his signal is better heard by the relatives who are further away.

6. Grassland animals such as gazelles tend to communicate at higher frequencies to avoid competing with the sound of the wind, occurring at lower frequencies. If a swarm of locusts settled in the area, how would the normal communication of grassland animals be negatively affected? Sketch a graph. Would forest animals fare better in the presence of a locust swarm?

7. Give three main sources of distortion for frequency modulated signals. Which is likely to have the largest affect in air?

Chapter 6: Sound reception

1. Explain how ears based on particle detectors and pressure detectors perceive sound.

2. Why does a pressure differential detector ear provide more directional information than a pressure detector ear?

3. Pressure differential detector ears sample the sound field at two different locations and compare them. Scientists can calculate the magnitude of the force exerted by an incident sound on a pressure-differential membrane using the following equation: F = (2πAPΔLcosθ)/λ where A = surface area of the membrane P = the incident sound pressure λ = the wavelength of the sound ΔL = the extra distance the incident sound waves (the distance between the two sampling points or ears) and θ = incident angle of the sound relative to the line which joins the two ears A scientist is studying the force that sound makes on a Mountain Eared – nightjar bird. She measures the radius of the bird’s membrane to be 1.4 mm and the length of the tube between the ears to be 4.6 cm. For sound of 2.5 cm wavelength incident at 26 degrees and a maximum pressure of 210 Pa, what is the force on the bird’s tympanum? What is the maximum force that this ear could detect for this sound pressure?

4. What is an otolith and how is it involved in fish hearing? Chapter 7: Light

1. Will blue or red light scattered more (diffractively) when small particles are present in the medium? Which wavelengths scatter more intensely? Why is this the case?

2. When sunshine passes through a triangular glass prism, it splits into a variety of color. This phenomenon is known as dispersion. Given that red wavelengths travel faster in glass than green wavelengths, why does this dispersion occur?

3. Using Snell’s Law, calculate how much red and blue light will bend at the surface of a glass prism if both enter the prism at a 30 degree angle with nair=1, and n2 = 1.52136 for blue and n2 =1.50917 for red. Which color bends more at the surface? By how much?

4. What is the difference between radiance and irradiance? Which one is more biologically important? Which one is easier to measure?

5. Sally has recently purchased a “diamond” pendent during her travels to India. However, she is suspicious of its authenticity and thinks it might be made out of glass. She thinks she can figure out which it is by seeing how much light reflects from the large flat surface on the front of the diamond since N(glass)= 1.5 and N(diamond)= 2.4. Explain how she could do this and what she would find under each possibility.

6. If life was discovered to have evolved underwater on Mars, would you expect the organisms to be able to detect X-rays, infrared, or visible light? Why?

7. Why is it important that light can travel in a vacuum unlike sound? Chapter 8: Light signals and transmission

1. There are four components of a visual signal that determine whether or not a receiver can detect the visual signal. What are these four components? Which can be easily varied? Are there ways to vary the other components?

2. In Finding Nemo while searching for his son, Marlin befriends Dory, a blue tang. Along their trek to find Nemo, Marlin and Dory escape several near-death situations including becoming dinner for a pack of ravenous sea gulls. Below Dory and the seagull, draw a simple diagram depicting the two different scattering mechanisms that result in their main body color. Be sure to identify which colors are being reflected or scattered, and the mechanisms responsible for each color.

3. If an animal wishes to be conspicuous, what combinations of colors should it use? What color combinations should it use to remain inconspicuous?

4. Draw a fish which displays countershading and reverse countershading on earth. Then draw countershading and reverse countershading on an alien planet where the light source is located under the water, not above it. Indicate the dorsal and ventral side of the fish in the picture. It may help you to draw the light source above or below the fish before you draw your fish.

5. Below are 4 different types of snakes each employing pattern and/or movement contrast. Discuss the types of contrast employed by each and discuss why they might look that way?

6. Compare the visibility of a seagull on a sunny cloudless day versus on a dark cloudy day. Discuss its visibility both from above and below, and how this may have influenced its white coloration.

7. Humans need light intensities of greater than 1 x 1010 photons / m2 sr sec in order to see. This is 10-10 as much as normal sunlight. In “clear” water the average attenuation coefficient of light is 0.12 m-1. Using this calculate the maximum ocean depth at which humans can detect light?

8. We know that giant squid can reach 60 feet in length and live in deep (1000 m) ocean water. Very little else is known. Using what you know about light transmission and squid behavior, make predictions about how squid signal to each other for mating and other purposes.

Light reception

1. Describe the process whereby a pigment cup eye, could develop into a camera lens eye in many generations. Give examples of organisms that have the intermediate forms.

2. When you go swimming and open your eyes underwater, everything looks blurry. Why is this? What difference does wearing swim goggles make?

3. Consider one organism with compound eyes and another organism with a camera style eye. Describe two main differences in how these two organisms perceive the world. Give an example of an organism with compound eyes.

4. What could a polarized light sensitive organism learn by looking at the sky and why? 5. Stimulation of more than one photopigment is necessary to distinguish colors. Sketch a

graph of the three human cone photopigments and explain why this is so. 6. Give four different ways that rods and cones differ. What are the specialities of each. 7. Consider the advantages and disadvantages of color vision. What type of environment

would encourage monochromatic vision? Synthetic questions S1. Compare and contrast when vocal communication or visual communication might be more appropriate and describe at least two factors that would determine when one is preferred over the other. S2. Light and sound can both be thought of as waves. While they have some similarities they also have differences. What happens when they encounter an air / water boundary? Name two similarities and explain two differences. S3. What are the five ways for an animal to produce vibration? Give examples for each. S4. In order to make a sound signal, an animal must produce vibrations, modify them in some way, and couple them to the medium in which the animal lives. What are some problems that animals face for each of these? Give an example that shows how an animal accomplishes each of these steps and overcomes the problems. S5. A species of crab lives in around a series of bubbling and therefore noisy thermal vents (assume bubbles < wavelength) on the ocean floor. Amazingly, they still manage to communicate with each other through auditory signaling. Name at least 4 ways in which their auditory signals differ from a species of crab that lives on the floor of a freshwater lake. S6. Male birds build display courts in the thick forest. There, they issue a series of calls to advertise their courts to females. These same birds preferentially forage in the open grassland. There, they issue an aggressive call to ward off male competitors. The two signals are described below. Which is the advertisement call and which is the aggressive call? Support your answer.

S7. What obstacles do fish face when receiving sound? How do they overcome these obstacles? S8. While you are fishing, you spot a fish in the water that appears to be close to you. When you attempt to catch it with a net, you realize that the fish is not in the spot where you saw him.

a. Why is your perception of the fish’s location distorted? b. Consider the refractive index of air (n=1.00) and the refractive index of water

(n=1.33). If a fish is at a 30 degree angle from the normal, where would the fish appear to be for a viewer outside of the water?

c. Consider the perspective of the fish. What would the fish see? What is a cone of darkness? Why is this phenomenon observed?

S9. Thinking about how we perceive the world around us: a. What makes the sky and the ocean appear to be blue? Are they the same processes? b. Why does the sky on the moon look black? c. Honeybees differ from humans in how they perceive light. What would they perceive about the sky? d. Why is the sky red at sunset?

S10. Compare between a fly, a trichromat gorilla, and a deep sea creature. What is their vision like and how does the eye structure differ to reflect the habitats of each. S11. The sensitivity of the human retina can be calculated using the equation we talked about in class. This is S=0.62A2Δρ2Pabs. Here, A is the limiting aperture diameter (in µm), Δρ=d/f is the photoreceptor acceptance angle, d is the photoreceptor diameter, f is the lens focal length and Pabs is the fraction of light absorbed by the photoreceptor. Eye resolution is determined by 1/Δρ.

a. How does increasing the focal length of the lens affect resolution and sensitivity? b. How does increasing photoreceptor diameter affect resolution and sensitivity? c. How does increasing the eye aperture affect resolution and sensitivity? d. How can Pabs be increased? e. If you are a diurnal organism, how might you increase resolution? f. If you are a nocturnal organism, how might you increase sensitivity (name at least

two options)?