Lecture 6.pdf

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University of Toronto St. George
Ecology & Evolutionary Biology
Michael Denny

Lecture 6Life Cycles Introductionthe annual cycle of a typical adult migratory North American bird consist of 4 components breeding moult wintering migration phases not independent of each othersuccess in one can depend in part on how the previous stage wentcan in turn affect future stagesenergy storage and transferhow much energy is left for the transition from one phase to another o birds cannot start migration until it has gone through premigratory fattening and reached a minimum body mass o some birds may skip a stage usually breeding if they cant go through all 4ultimate control of annual cycles seasonalityeffects food supply o main proximate factor endogenous rhythmslinked to daylengthBasic Life Cyclethe songbird Whitecrowned Sparrow is an example of a temperate breeding migratory songbirdo exhibits marked geographic variation o 5 subspeciesthe annual cycle of a typical adult migratory North American bird includes 2 annual moults a breeding season a premigratory fattening and a wintering periodbreeding activities substages include courtship pairing nest building egg laying raising and fledging youngsedentary species have simpler life cycle postbreeding molt some degree of winter fattening prebreeding molt gonadal maturation and breedingBreedingex C capensis breeds in the Hudson Bay lowlands100 frostfree days to complete breeding and moultmales arrive before females in late May to establish territoriesdefended using song and aggressive chases of trespassing neighboring conspecificsthe territory functions as a feeding areaalso attracts femalesbeing able to hold a territory is an important prerequisite to pair formationpair formation and mating occurs soon after female arrivesnest building is done by females alone takes about 5 days o nest would usually sit on the low branches of TamarackNorthern Labrador Tea shrubsafter a short prelaying period after female accumulates dietary calcium needed for the eggs oviposition takes place one egg is laiddayfinal clutch is usually 3 daysthe female alone would incubate the eggs for about 12 dayschicks hatch blind and mostly naked some natal downmale now helps the female feed the chicksbirds must gather fresh food for the chick continuouslyby day 10 the chicks grows juvenile plumage including flight feathersby day 14 they can make short flights and leave the nestfor another 20 days the parents will continue to feed them Control of Seasonal Breedingmost birds are seasonal breedersbirds are longday breedersmate and incubate eggs and rear young in the spring and summer when daylength is longthey have rapid development timescan complete their breeding cycle during the warmer productive period of spring and summerin contrast domestic mammals such as sheep and cows are shortday breedersmate in the fall and gestation occurs in the winter o give rear birth and rear their young in spring and summercoincides with peak food abundanceHPGAxisseasonal breeding of birds is regulated by the hypothalamicpituitarygonadal axis HPGaxis
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