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Lecture 18: Annual Cycles I.
Annual Cycles (Chapter 11) a.
Competing demands
i.
Breeding
ii.
Molting
iii.
Migration (for some) b.
selection to minimize overlap (review overhead) c.
timing?
i.
Hormones, proximately
ii.
Daylength, ultimately, in most cases
iii.
Wet/dry season
iv.
Also food supply (Barn owls) d.
Circadian vs. Circannual rhythms
i.
inherent as shown by exposing birds to constant
light
ii.
but drift - cycle needs constant resetting - Why?
iii.
some annual cycles 6-9 months in the tropics e.
Tropical species wet/dry seasons
i.
Breed
ii.
Molt
iii.
survive to next cycle f.
Temperate/arctic species - temp and daylength
i.
Breed
ii.
Molt
iii.
Migrate (in some species)
iv.
survive to next cycle g.
Timing is everything
i.
avoid famine 1.
peak food availability 2.
usually spring
ii.
breed (molt) when food is abundant 1.
but Eleonoras Falcon in fall to catch migration 2.
Barn Owls breed whenever theres enough food
iii.
breed when mates are available
iv.
avoid overlap of molt and breeding as much as
possible 1.
raptors female molts first 2.
hornbills - female does complete molt in nest
cavity
v.
Normal sequence is 1.
Breed 2.
Molt 3.
Migrate 4.
Lots of variations 5.
some species do not complete molt before migration
e.g. Redtails on MVY h.
How does timing work?
i.
first, its remarkably sensitive - 5-10 minute
change in daylength stimulated gonadal activity in Rowans 1929 study of
Dark-eyed Juncos
ii.
Pineal gland important, but not photoreceptor as
shown by removal of Pineal
iii.
Mammals measure daylength visually, birds via
receptor DEEP in brain!- Hypothalamus 1.
neurohormones released in hypothalamus stimulate
anterior pituitary to release gonadotropic hormones Top - Home - Habitat Fragmentation - Neotropical Birds - Birds of Prey - Project Osprey Watch - Project Barn Owl - Graduate Students - Conservation Organizations - Publications - Ornithology |