9/23/2019 1 PSY 2364 Animal Communication Figure 1 Animal signals Mark E. Laidre, Rufus A. Johnstone Current Biology 2013 23, R829-R833DOI: (10.1016/j.cub.2013.07.070) Midterm • Wednesday October 2 – midterm exam • Midterm exam review sheet is posted on the course web page http://www.utdallas.edu/~assmann/PSY2364 Sound localization • Marler (1955) first studied alarm calls in different species of small passerine birds and found important acoustic similarities: – Single, brief duration “seet” call – Low amplitude – High frequency (narrowband) – Gradual onset Sound localization • Marler (1955) found that mobbing calls are repeated, loud calls that attract others. Unlike alarm calls, mobbing calls consist of: Repeated series of loud “chuck” calls Wide range of frequencies (broadband) Sudden sharp onset and offsets Sound localization • Marler suggested that alarm signals are shaped by strong selection pressures. Alarm calls reveal a clear trade-off between detectability and localizability. • Small animals are better at detecting high frequencies than larger animals (e.g. predators) • Sounds with a narrow band of frequencies and gradual onsets and offsets are hard to localize.
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PSY 2364Animal Communication
Figure 1
Animal signals Mark E. Laidre, Rufus A. Johnstone Current Biology 2013 23, R829-R833DOI: (10.1016/j.cub.2013.07.070)
Midterm
• Wednesday October 2 – midterm exam
• Midterm exam review sheet is posted on the course web page
http://www.utdallas.edu/~assmann/PSY2364
Sound localization
• Marler (1955) first studied alarm calls in different species of small passerine birds and found important acoustic similarities:
– Single, brief duration “seet” call
– Low amplitude
– High frequency (narrowband)
– Gradual onset
Sound localization• Marler (1955) found that mobbing calls are
• Marler suggested that alarm signals are shaped by strong selection pressures. Alarm calls reveal a clear trade-off between detectability and localizability.
• Small animals are better at detecting highfrequencies than larger animals (e.g. predators)
• Sounds with a narrow band of frequencies and gradual onsets and offsets are hard to localize.
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Marler’s hypothesis
1. Small animals are better at detecting high frequencies than larger animals (e.g. predators)
2. Sounds with gradual onsets and offsets are hard to localize
3. Narrowband sounds are harder to localize than broadband
4. High frequencies are linked to fear rather than attack
5. Mobbing calls are repeated in a loud voice to attract others
Alarm call detection
1. Amplitude of signal at the source
2. Attenuation characteristics of environment
3. Signal-to-noise ratio at the receiver
4. Sensitivity and discrimination ability of the receiver
Depends on:
Adaptation hypothesis
• Any given sound in the repertoire of a species has been favored by natural selection because its influence on the behavior of other animals is beneficial(i.e., raises the fitness of) the sender and/or his or her close relatives.
Marler’s hypothesis
• Marler (1955) identified some important acoustic differences between alarm calls and mobbing calls in song birds. What were these differences, and how did Marler link these properties to the different functions that these calls serve?
Marler, P. (1955). Characteristics of some animal calls. Nature 176: 6-8
Ecological constraintscommunicating via sound waves
1. energy costs2. overcoming environmental obstacles3. locatability of the source 4. rapid fading5. range of physical complexity
Advantages of sound
1. Sound bends around objects (leaves, tree trunks) that are opaque to visual signals
2. Allows for very rapid changes in pattern
3. Can be more precisely timed than chemical signals
4. Rapid signal decay5. More precisely localizable than
chemical signals
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Advantages of sound
6. Useful for small or cryptically colored species (grasshoppers, crickets, frogs, birds), animals that are nocturnal, or live in dimly lit environments.
7. Large body size allows whales and elephants to produce high intensity, low frequency sounds. Both of these properties increase the range (distance) over which they can communicate with conspecifics.
Design features for long distance communication
• Calling individuals select particular depths and channel sounds so that they are detectable over a range as much as 100 miles.
• High intensity, low frequency sounds, large body size, good signal-to-noise ratio.
Honest Signaling
• Rubenstein & Alcock, ch. 8
• Less contact and fewer aggressive interactions with mating rivals in male European toads when calls were higher in frequency.
• Higher attack rate with small toads (top left) compared to large toads (top right).
Davies and Halliday, 1978
Vocal signals and body sizeOptical Communication
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Optical Communication
• Radiant energy from the visible range of the spectrum of electromagnetic radiation
• Sources of light: the sun, burning objects, lightning, artificial (man-made) lights, bioluminescent plants and animals
• The human visual system is sensitive to light wavelengths between approximately 380 and 750 nm (or frequencies between 400 and 790 THz), spanning just under 1 octave (a doubling in frequency), which we perceive as the spectrum of colors. In contrast, the human auditory system is sensitive to sound frequencies between 20 Hz and 20,000 Hz, or approximately 10 octaves, which we perceive along the dimension of pitch. (Oxenham, 2019)
Properties of light
• Different frequencies of light are perceived as different colors
• Light varies in intensity
• Light follows the inverse square law
• Wavelength-specific and medium-specific attenuation (selective filtering)
• Light is directional
Properties of light
• Light speed varies depending on the medium, so light shows 3 other properties in common with sound:– reflection
– refraction
– diffraction
Factors affecting opticalsignal transmission
• Absorption- optical energy is lost (absorbed) as it travels through the medium.
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Factors affecting opticalsignal transmission
• Diffraction- light waves bend and spread out as they travel through a narrow aperture.
– Diffraction effects are pronounced when the propagating wavelength is similar in size to the diffracting object
Factors affecting opticalsignal transmission
• Reflection- Optical energy is redirected when it strikes a surface, usually back to its point of origin.
Factors affecting opticalsignal transmission
• Refraction- is the change in direction of a wave due to a change in its speed, most commonly observed when a wave passes from one medium to another.
Optical Communication
• Badges are morphological specializations used as visual signals, such as bright patches of skin, fur, or feathers, horns, casques, or crests.
Males are attracted to the species-specific flashing patterns emitted by females.
Predatory fireflies of a different species, Photuris, mimic the species-specific flashing pattern of a Photinus firefly to attract and eat the male.
A female Photuris firefly eats a male Photinus ignitus to obtain defensive compounds called lucibufagins which are distasteful to predators.
Proceedings of the National Academy of Sciences (Sept. 2, 1997, Vol. 94, pp. 9723-9728)
Visual systems
• Vision provides a means of detecting objects in an animal’s surroundings.– Luminance (intensity differences; brightness)
– Reflectance (spectral composition; color)
• Vertebrate visual systems contain two types of receptors:– Rods are more sensitive in low light conditions
– Cones function in daylight and provide the basis for color vision
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Vision
• Visual systems have evolved to detect light.
• This requires trapping the electromagnetic energy and absorbing it by a receptor molecule. This process triggers an electrical response in the receptor neuron.
Properties of color
• Brightness (intensity)
• Hue (dominant wavelength or frequency)
• Chroma (degree of saturation or purity of the dominant frequency)
Rods and conesTrichromatic Color vision
• Human color vision depends on interactions of three types of cone cells in the retina of the eye, each sensitive to a range of wavelengths of light.
Color vision
• Cone cells in the retina contain a pigment derived from a protein (opsin) linked to a small molecule called retinal. The pigment absorbs light energy (photons) which activates retinal neurons, generating action potentials in the optic nerve.
Color vision
• Two different wavelengths of light can produce the same pattern of activation in a cone cell. The outputs of the cone receptors are combined and must be compared at a higher level of the visual nervous system. Color vision result from a decoding of the outputs of the color receptors by the brain.
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Color vision
• Color vision in birds, lizards, turtles and many fish is based on four types of cone cells (tetrachromatic color vision). These animals can distinguish colors in the near ultraviolet range of the spectrum.
• Old World primates and humans have three color receptors; most mammals have only two types (dichromatic color vision).
Goldsmith TH (2006). What birds see. Sci. Am. 69-75
Color vision
• Evidence suggests that the progenitors of mammals lost two of the four types of cone cells during a period in their evolution when they were mainly nocturnal (and color vision was less important for their survival).
Goldsmith TH (2006). What birds see. Sci. Am. 69-75
Color vision
• African monkeys, apes and humans “reclaimed” a third cone through duplication and subsequent mutation of the gene for one of the remaining pigments.
Goldsmith TH (2006). What birds see. Sci. Am. 69-75