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bird songs.docx

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Brett Beston

March 11 , 2013 Psych 2TT3: Animal Behaviour Bird Song Bird Song - why bother? - how do birds sing? - Why do animals sing? - Is bird song innate or learned? - How do birds elarn how to sing? - Why do some birds learn how to sing? Bird Song – Why Bother? - vocal signals are ubiquitous - birds a classical model - vocal learning occurs only in 3 mammal & 3 bird taxa - vocal learning has allowed the evolution of language - neuroscience and evolution - most birds sing however if we look at all the different varieties of birds, only 3 of them actually learn something throughout their lifetime - this means all other orders have innate song behaviour - what is the benefit of learning in certain occasions vs. not learning - what are the proximate causes? What is Sound? - sound are pressure waves traveling through a medium - in air (and water) molecules are packed together at different densities, depending on the air pressure - sound pressure waves are relative to the ambient air pressure - alternative pressure waves or particles Ambient Air Pressure - differences in air pressure - string vibrating back and forth creates differences in air density or pressure - low pressure are less densely packed than high pressure - as a result of vibrating string we get oscillations of high and low density A Sound Wave - height is the amplitude = loudness or volume - frequency, how often or how tightly spaced are the air packets, includes peak and valley = pitch, the tighter the waves the higher the pitch - only in pure tones Complex Waveforms - sine waves do not occur in nature - they must be artificially created - naturally occurring sounds are complex waveforms - no indication of a pattern - you can have two different people say the exact same thing yet the characteristic of sounds would be very different Sonograms - used to represent sound - looks at frequency - at the bottom is digital representation of sound waves - above is the actual sonogram - we characterize amplitude and frequency change - frequency is on the y-axis, the higher the bands, the higher the frequency - amplitude is based on the darkness of the dots - red specs represent sounds that are so loud that have actually saturated the recording machine - white crowned sparrows derived from different population have variation in the sound that they produce - can identify where a bird is from and be able to replicate the sound - very important to studying song The Larynx (Humans) - organ in our throats which allow for sound production The Syrinx - special membranes (MTM) vibrate when air from lungs is forced over them - two passages in which air can pass - medial membrane: contractions can change the articulation of sound - sounds are coming from two different tubes means that we can produce two different sounds at the same time, can sing continuously - found deep in the chest - can produce two different notes simultaneously - by alternating between high and low notes the song can carry very complex messages - signals originated somewhere else in the brain Song Control in the Brain - using fMRI scan - different regions involved in learning and production of song - production of song: the higher vocal center  dense collection of neurons  sends information down through pathway of connections  branding the RA (robust nucleus)  information is then sent from RA to nXIIts  hypo glosal nerve (nerve 12), information is sent to tracial syrinx - if you damage these areas you completely disrupt the production of song - we can also make recordings of songs and trace neural firing that starts in the higher vocal center - motor: HVC, RA and nXIIts - learning: LMAN (lateral magnocellular nucleus of the anterior neo) and area X 21 Century Research - recording from individual neurons - monitoring gene expression - evolutionary genomics of song and language Expression of the ZENK Gene in Canaries - expression is linked to activity in only certain areas - expression of gene ZENK following exposure to certain sounds - ZENK is labelled - Canaries have been reared under certain conditions - Silence: only sparse distribution of ZENK expression, not being active - Hearing only, cannot produce song: more diffuse expression of ZENK but not particularly centralized in any way - We only see expression of ZENK in song production - Singing only: although a bird may be capable of producing sound they don’t get any feedback and cannot go through trial and error - When they can hear and sing we see concentration of ZENK in the LMAN, the only case that can actually lead to learning Individual Neurons - in HVC: activation of just a few neurons - RA: leads to amplification of signal in RA, lot more activation, RA is not just a relay station - Muscle activity: in vocal cords - Songogram: measure and record the actual production of sound In Birds, Who Sing? - typically only males sing  genetic (chromosomes)  males ZZ  females ZW  which translate into environmental differences in the birds brains  environmental (hormones)  if we look at chicks hatching in the early developmental stages before maturation, the circulation of hormones influences brain development  high levels of estrogene increase song learning ability The HVC (Higher Vocal Centre) is Larger in Males than Females - equal density at ten days - decrease in females brain - increase in males brain - subject females to estrogene treatment eliminates reduction in density of HVC neurons - strong role in preventing cell death Because of Sex Differences in Neuronal Death Rate - role of estrogene is preventing cell death Males have a Larger RA - in a male it is roughly 5 times the size - seems to vary between sexes as a result of neurological differences Song Repertoire is Positively Correlated with HVC Volume - positive correlation between HVC volume and the number of songs they are able to produce Why do Animals Vocalize? - what does an animal gain as a result of being able to vocalize - how does producing more songs help them? - How it plays a role in attracting females and competition between other males for resources and territories - In some species, both sexes produce vocal signals - Is vocalization used:  For social interactions?  For sensing the environment  Intentionality: warning calls in prarie dogs  Navigating their environment  Birds can do a combination Why Sound? - better than vision in poor lighting and places with obstacles (forest) - humans depend highly on vision - limited ability to see in a forest, a vocalization is a form of communication with indicates whereabouts without the need for visual stimuli, and can communicate possession - sound is useful when visual information has been degraded Attracting Mates? - how does singing correspond to different aspects of mating When do Birds Sing? - frequency of song in sedge warbler and reed warbler - there is seasonal variation in song production - as we get into may there is a large peak in song production - and decreases and falls to baseline levels in june/july - male singing precedes the laying of eggs in a nest - how does finding a mate affect ability to sing - dawn chorus: density of air, so the sound travels the furthest it can possibly go and that is when they sing the most - after pairing they stop song production - in 2 european warblers, singing starts 6-12 days after arrival - singing stops or is limited after pairing Experimentally Inducing Birds to Sing in Great Tits - remove females from great tit territories - record singing by the males - increase song production w
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