Lecture 10.pdf

6 Pages
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Department
Ecology & Evolutionary Biology
Course Code
EEB386H1
Professor
Michael Denny

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Description
Lecture 10 Feeding Ecology IntroductionModern birds have lost their teeth and replaced them with a horny beak coveringBeak size shape and function has diversified hugely and combined with cranial kinesis they can exploit a wide variety of prey captureThey can store food in an outpocketing of the oesophagus and they have a twochambered stomach in which the muscular gizzard portion can efficiently process foodTogether these adaptations have probably contributed to modern bird successBird BeaksThe bird beak consists of the bones of the upper and lower jaws and their keratin covering called the rhamphothecaThe beak is not just a bird feature living turtles and monotreme marsupials eg platypus and echidna have a beak and there were beaked dinosaurs ornithomimids ostrich dinosaursThe rhamphotheca is a simple sheath in most species but some like the tubenose seabirds eg albatross have a beak composed of plates compound rhamphothecaTomiaThe cutting edges of the rhamphotheca tomia especially the mandibular tomia helps secure prey in the beak they are not used to process food in the beakFisheating birds such as mergansers have serrate tomia to grip preyA variety of mainly insecteating birds have brushlike tomia scopate tomiaFlamingoes and some waterfowl have baleenlike tomia which act as strainers to filter food particles from waterThe mandibular tomia of geese are used to crop grassFunctional Morphology of Beak Opening and ClosingThe birds skull is kinetic cranial kinesis the upper jaw can move independent of the craniumIn prokinetic beaks the upper jaw flexes upwards at the craniofacial hinge a region of flexible boneSome species can also flex their upper jaw midway along the jaw rhynchokineticThe opening of the upper jaw in birds involves a mobile quadrate and linked elements in the palate as well as the jugalIt is the light beak combined with cranial kinesis that makes the birds beak such an excellent prey capture and manipulation toolCranial kinesis likely functions in a number of ways o increased gape o greater control of the jaws and gape eg singingo increased ability to feed selectively o shock absorbance and engineering safety o tool useSeed HuskingA forceful bite of the lower jaw cracks the seed and the lower jaw is pushed in the crack like a chisel between the husk and kernel to the other end of the seedThe lower jaw motion stops and the lingual tip rotates the seed 180 while the lower jaw tip edge is kept continuously fixated at the cut edge of the seedOnce the seed is in the reversed position the lower jaw husks the other side of the seedThen the husked seed is transported by lingual inertial actionLarge kernels are often bitten to pieces which is called chewing and each piece is stored until a bolus is formed and swallowedCranial KinesisCranial kinesis is the term for significant movement of skull bones relative to each other in addition to movement at the joint between the upper and lower jawrelative movement between the upper jaw and the braincase can move upper and lower jawfine forceplike manipulationwithout compromising visual planeallows extraction of small preyloss of teethexpands foraging nichesincreases gape
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