behaviour 4

• Ear structure in birds, reptiles and amphibians

  • Basically the same as a human ear (mechanical movement of the sensory hair cells), but they only have one inner ear bone
• Amplitude

  The maximum extent of a vibration or oscillation, measured from the position of equilibrium
• Frequency


  The rate per second of a vibration constituting a wave, either in a material (as in sound waves) or in an electromagnetic field (as in radio waves and light)
• Wavelength


  The distance between successive crests of wave, especially points in a sound wave or electromagnetic wave
• Human hearing declines with old age

  Due to the damage to the sensory hair cells in the cochlea
• Birds (for example) can repair hair cells, so their hearing does not decline with age
• Mammals

  • Most have mobile pinna (external ears) which can be independently moved to be able to localise the detection of the sound
• Some mammals (e.g. dolphins, seals) do not have mobile external ears as it would impede their locomotion
• Some mammals' external ears also help with thermoregulation
• Fish bodies

  About the same density as the water, so sound waves in the water travel 'through' the fish such that the fish cannot hear them
• Spiders

  • Do not have ears, but jumping spiders can sense sound via tiny hairs on their forelegs, and bridge spiders use their web as a sort of 'ear drum' to help detect sounds
• Animals use the relative difference in time to reach each ear to indicate direction, but this is increasingly difficult as the animal gets physically smaller
• Most vertebrates appear to use ears to detect the general direction of a noise, but then they orientate their head so that they can use their eyes to identify what they have heard
• Barn owls

  • Have flight adaptations to reduce noise including broad wings to allow slow flight with low wing-beat frequency, barbs on the leading edge of the wing, velvety surface on the wing, and fringes on the trailing edge
• Once animals had evolved the ability to detect sound, many then evolved the ability to create sounds, leading to a proliferation of intra-specific communication, mostly for the purpose of reproduction
• Stridulation

  The act of producing sound by rubbing body parts together, with one part typically acting as a plectrum
• Tymbalation


  The act of producing sound by vibrating the tymbal, a corrugated structure on the exoskeleton
• Tremulation


  The act of producing sound by vibrating a non-specialised body part
• Very long distance contact calls can only be made by large animals due to the high energy required to produce the calls
• Baleen whales have a free-floating ear that is detached from the skull so they can hear higher pitches, as their bone vibration from infrasound would otherwise prevent them from hearing higher frequencies
• Percussion calls


  A type of animal communication that involves hitting or tapping a surface to create vibrations that can be detected by other animals, different from vocal calls
• Percussion calls


  • Some elephants use their feet to produce seismic signals that can travel long distances through the ground
• Organisms cannot help but shed molecules from their skin / fur / feathers, mouth, intestinal tract, and many species also release molecules deliberately for communication
• Lots of plants also emit a wide range of odours, some relating to communication between plants themselves, and others involving communication with animals
• Smell was probably the first sense to evolve, as it does not require a specialised sensory organ like sight and hearing
• Unlike sound and light, smell cannot be measured on a scale, as organisms can detect a very wide range of different molecules, even if they have similar structures
• Smell


  Advantageous as the transmission of odours is dependent on the rate at which they diffuse through a medium from their source, relating to the physical properties of the odour molecules
• Smell and taste require chemicals to be dissolved in a liquid before they can be detected
• Smell


  Relates to chemicals entering the nose and stimulating the olfactory nerve, sensing things in the environment (food, prey, predators)
• Taste


  Relates to chemicals entering the mouth and the mouth responding to substances dissolved in saliva
• Dolphins do not have an olfactory nerve so they cannot smell, and can only taste salt
• The majority of bird species' capability for smelling is still quite controversial, but being investigated more intensively
• Cats cannot taste sweet things because they need meat for several essential amino acids
• Fish have paired nares (nostrils), and the odours in water are already dissolved in the medium
• Species like the catfish have taste receptors all over their body, meaning they can taste with their skin
• Most insects have sensory organs (sensilla) on their antennae to detect airborne chemicals, and use a wide range of body parts for detecting taste (antennae, palps, proboscis and legs)
• Pheromones


  Chemicals that facilitate communication between animals of the same species, eliciting a very specific change in behaviour
• Apocrine and Holocrine glands

  The two types of specialised glands in mammals that make odours
• Allomones

  Chemicals that facilitate communication between animals of different species, to the advantage of the sender but not the receiver