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Avian Specializations

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Avian Specializations Avian specializations Chapter 17 Mesozoic bird radiations • Enantiornithes – metatarsals are fused differently than modern birds, also retained teeth – Dominant in the cretaceous • Ornithurines – appeared later in the cretaceous, variety of ecological types Modern birds • Neornithes – late cretaceous – about 9672 extant species – Split into two major groups • Palaeognathae (Ratites) • Neognathae Feathers • Calamus – anchors feather to skin • Rachis • Barbs Feathers • 5 types of feathers – Contour feathers • Remiges –wing feathers • Retrices – tail feathers – Semiplumes –large rachis with plumulaceous vanes – Down –entirely plumulaceous and rachis is shorter than the longest barb or absent – Bristles – stiff rachis and barbs only at the base or absent – Filoplumes –fine hairlike feather with few short barbs at the tip, used for sensory Skeleton • Pneumatic bones • Bone fifusions – Synsacrum – Pygostyle – Furcula – Tarsometatarsus – Tibiotarsus Muscles • Flight muscles account for 25 to 35 % of total body mass of strong fliers • With birds that rely more on running more mass may be in the leg muscles than in flight • Lig ht and dkdark meat – Dark meat has the presence of myoglobin which idiindicates a hig h capacity for aerobic metablibolism – Light meat has little capacity for aerobic metblitabolism Avian wing • Wing produces lift and forward motion. • Primaries are mostly responsible for propelling • SdiSecondaries for lift • Lift –vertical force equal or greater than the weight of the bird • Drag –force that is opposed to fdforward motion of the bdbird through the air Avian Wing • Wing loadings (mass of the bird divided by wing area) Flight • http://www. youtube. com/watch?v=ssrv89x7Q 2U • http://www. youtube. com/watch?v=31Xw75h AwIc • h//http://www.youtu be.com /watc h?QIfi9h?v=vQIsfi9vae Q Flight muscles • Pectoralis – pulls down on wing • Supracoracoideus – lifts wing • Both muscles originate on the sternum Basic wing types • A) dynamic soaring – needs strong persistent wind • B) Elliptical –forest species for rapid, slow flight and high maneuverability • C) High aspect ratio – typical of fast strong fliers • D) High lift – static soarers, marked slotting in primaries, seek out rising air masses Bird feet • A) anisodactyl • B) zygodactyl –toes 2 and 3 forward i.e. parrots and woodpeckers • C) heterodactyl –toes 3 and 4 forward, only in trogons • D) syndactyl – iei.e. belted kingfisher • E) pamprodactyl all toes forward, swifts Beaks Tongues • Some woodpecker tongues can be extended 4X the length of the beak, have barbs on the end for impaling bugs in wood tunnels • Hummingbirds and sunbirds the tip of their tongue is divided into thin hairlike projections that nectar adheres to by capillary force Digestive system • Crop – enlarged portion of the esophagus for temporary food storage, also used to feed nestlings, doves produce a nutritive fluid (crop milk) that they regurgitate for their offspring Digestive system • Stomach – 2 relatively distinct chambers – Proventriculus –anterior glandular stomach – Gizzard – posterior muscular stomach • A turkeys gizzard can crack nuts that require 50‐150 kg of pressure to break • Gut length changes –birds that eat different types of food over different season can change the length of their gut. (also a change in diges tive enzymes) Vision • Different eye shapes are basically a function of fitting a large eye in a small skull Hearing • For the most part birds hear about as well as humans, Owls being the main exception. • Owls have a facial ruff that acts as a parabolic sound reflector and they also have assymetitries in the shape of the ruff and the skull Olfaction • Most birds have a ppyoorly developed sense of smell • Some exceptions – Kiwi – Turkey Vulture Vocalizations • Bird songs are sppyecifically the breeding calls of many bird species • It is a learned behavior • Indigo Bunting • http://www.learnbirdsongs.com/birdsong.php?id=19 • Wood Thrush • http://www.learnbirdsongs.com/birdsong.php?id=32 • Lyre bird • http://www.youtube.com/watch?v=VjE0Kdfos4Y • Paired with visual displays • http://www.youtube.com/watch?v=ARVbLaYbSjo • http://www.youtube.com/watch?v=bRQgYjKaGek Mating systems • Two broad categories – Monogamy – Polygamy • Polygamy can be exhibited by: – Males = Polygyny – Females = Polyandry – Both sexes = Promiscuity Social Monogamy • Share responsibility for clutch but have extra‐ pair copulations • Benefits for both sexes – Increase fitness – Increase heterozygosity • Male benefits – Sire more offspring – Another male cares for his offspring – Spreading reproductive investment • Female benefits – All eggs fertilized – Increase fitness mating with higher quality male – Quasi nest parasitism Nests • Large variety in nests and nesting behavior • Not all birds construct nests or even care for their own eggs • Brood Parasites Eggs • Oviparity – why haven’t birds evolved viviparity? Viviparity has evolved many times and also in other sauropsids. What is the advantage of Oviparity in birds? Offspring • Two main types – Precocial – Altricial Migration • About 40% of bird species in Palearctic are migratory • Advantages = food resources, avoid temperature stress, longer summer activity periods • Cues –internal rhythms and external stimulus – Day length – best indicator .
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