BIOL 329 Lecture Notes - Lecture 19: Monomorphism, Natural Selection, Snowy Owl
6 May 2018
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Lect 19
Ducks (sexual dimorphism) vs Loons + Grebe (sexual monomorphism).
Natural selection has favored the same type of plumage (monomorphism) for the requirements of
biparental care. Exceptions: Belted kingfisher and snowy owl – both have biparental care yet are
sexually dimorphic. They are dimorphic because they are foraging in different habitats.
White underparts in gulls function as hunting camouflage. When tested, fish could see black underside
much better than white underside. At equator, black belly more common; moving towards the poles:
white belly. Birds that are all white have denser feathers than birds that are all black. Black seabirds
roost in protected sites, white birds roost in exposed sites – need thick feathers to survive through the
ight. White irds hae higher aledo so they do’t oerheat due to their thick feathers.
Theral ipat of igratig irds’ ig olor o their flight perforae: oC differee etee
feathers on top and below. Bird gliding in cold conditions – more challenging because cold air causes
ore drag it’s ore isous. Dark ig color on top increases the temp of the boundary layer –
reduces drag force.
Bald eagle: mature in 4th or 5th year. Why do they switch plumage between sub-adult and adult? Why a
white head and tail on a raptor? Species recognition? What do they look like from the perspective of
their prey and from their predators? Dark brown to camouflage in the forest – does’t matter to their
prey if they are scavengers. White head as a display of sexual maturity?
Comparative analysis: look at a related species to see if they have the attribute OR look at an unrelated
species and see if they have the attribute and what their life history is. African fish eagle: white breast,
unrelated to bald. White-bellied sea eagle (Aus): white down entire ventral surface. Brahminy Kite (SE
Asia) – feeds on fish. Osprey – looks similar to white-ellied sea eagle. Stellar’s sea eagle largest: white
legs and head. How the prey sees the predator may influence functionality of coloration.
Loons of BC
All are piscivorous. Previously thought to be one of the oldest groups of living birds. Somewhat similar to
later Mesozoic Hesperornis. First unambiguous fossils in early Eocene. Feet far back on body. Heavy
wing loading. Two juvenile molts – down, down-feathers, and feathers.
find more resources at oneclass.com
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Document Summary
Ducks (sexual dimorphism) vs loons + grebe (sexual monomorphism). Natural selection has favored the same type of plumage (monomorphism) for the requirements of biparental care. Exceptions: belted kingfisher and snowy owl both have biparental care yet are sexually dimorphic. They are dimorphic because they are foraging in different habitats. White underparts in gulls function as hunting camouflage. When tested, fish could see black underside much better than white underside. At equator, black belly more common; moving towards the poles: white belly. Birds that are all white have denser feathers than birds that are all black. Black seabirds roost in protected sites, white birds roost in exposed sites need thick feathers to survive through the (cid:374)ight. White (cid:271)irds ha(cid:448)e higher al(cid:271)edo so they do(cid:374)"t o(cid:448)erheat due to their thick feathers. Ther(cid:373)al i(cid:373)pa(cid:272)t of (cid:373)igrati(cid:374)g (cid:271)irds" (cid:449)i(cid:374)g (cid:272)olor o(cid:374) their flight perfor(cid:373)a(cid:374)(cid:272)e: (cid:1005)(cid:1004)oc differe(cid:374)(cid:272)e (cid:271)et(cid:449)ee(cid:374) feathers on top and below.
