Moult

Question 1

Evolution of feathers

Answer 1

Despite the complex structure, one can trace the origin of feathers to simple reptilian scale. Beta keratin in feathers are derived from reptile scale beta keratin.

Question 2

Five step model to explain the evolution of complex feather structures

Answer 2

The model provides a mechanism and plausible function for each step in the chain.

Question 3

Feathers are dead once formed

Answer 3

New feathers grow in the same follicles and pushes the old feathers out as they grow. With the exception of penguins and mousebirds.

Question 4

Pterylae

Answer 4

Specific tracts with follicles where feathers grow in.

Question 5

Feathers wear out

Answer 5

By UV light
Abrasion
Feather lice
Bacteria
Fungi

Question 6

What slows the rate of wear of feathers?

Answer 6

Melanin

Question 7

Moult

Answer 7

Process by which feathers are replaced.

It is mostly scheduled but can replace damaged feathers by the use of shock moult.

Question 8

Shock Moult

Answer 8

Replacing of feathers when trauma has occurred. Not scheduled.

Question 9

Cost of moult: Direct costs

Answer 9

Feathers are expensive to produce. Keratin requires a lot of amino acid cysteine (sulphur). Scheduled moult is linked to major physiological turnovers. Stressed birds struggle to grow new feathers.

Question 10

Cost of moult: indirect costs

Answer 10

Moulting affects feather performance thus affecting flight. This is worse for birds with high wing loading, some birds compensate by decreasing their body mass. It also affects their signaling, and insulation and drag.

Question 11

Maximizing performance

Answer 11

Because mounting is costly, it tends to avoid overlap with other costly activities such as breeding and migration. Thus a balance needs to be struck between moult speed and feather quality, as fast growth results in poor quality, short lived feathers.

Question 12

Reduced survival of wintering tits

Answer 12

Delaying moult in Blue tits resulted in faster moult, and less insulation. Experimental birds had lower overwinter survival, and those that survived raised fewer chicks the following year.

Question 13

Poor flight feathers in starlings

Answer 13

Accelerating moult in Common starlings resulted in shorter, lighter primary feathers with thinner rachis that were less symmetrical, weaker and less rigid, causing faster wear.

Question 14

Chicks race against predation

Answer 14

Chicks in the nest are subject to high risks of predation, thus selection favors chicks that fledge as young as possible. But fast feather growth results in weak contour feathers that have to be replaced within a few weeks of fledgling. Rapid growth also compromises the immune system.

Question 15

Juvenile feather quality

Answer 15

Juvenile contour feathers are lighter and have fewer barbs than adult feathers. The effect is greater in birds with very short fledgling periods.

Question 16

A few birds do moult while breeding

Answer 16

Female raptors and some seabirds moult while breeding.mthe most extreme case however are female hornbills which replace all flight feathers while cemented in their nest hole and thus are entirely dependent on the male for food.

Question 17

Moult in Penguins

Answer 17

They replace all their feathers at once, which takes longer than larger species. This causes them to go on a fast for 15-34 days losing about 40-45% of their body mass.

Question 18

African Penguin: Moult

Answer 18

Adults when they are greater than 15 months, they have a striking plumage which allows them to swim faster and fish cooperatively on schooling fish. Juveniles, younger than 15 months, have cryptic plumage thus are slow swimming and target solitary fish and are vulnerable to predation.

Question 19

Two mounting strategies in flying birds

Answer 19

Rapid, flightless moult

Protracted moult

Question 20

Rapid, flightless moult

Answer 20

Limits the exposure period, but puts the bird at a greater risk while flightless
Mainly large water birds.
They get over the moult quickly but need a safe moult site. Some species even take up specific moult migrations.

Question 21

Protracted moult

Answer 21

Spreads the cost over a long period but creates problems by avoiding other stressful activates such as breeding and migration.

Question 22

Process of flightless moult

Answer 22

Multiple flight feathers are lost. Pin feathers then begin to develop. Flight feather shafts begin to harden, and finally flight feathers become fully formed.

Question 23

Implications of fixed growth rate

Answer 23

Feather growth rate is a key constraint with approximately 2-8mm per day.
Exacerbated by the trade off between the growth rate and the feather quality,. East growth results in short lived feathers.

Question 24

Bigger birds have larger flight feathers

Answer 24

As birds get larger, feather length outstrips feather growth rate. Only a modest increase in feather growth rate with increase in bird size

Question 25

Large birds don’t moult all primaries each year

Answer 25

Multiple waves of moult minimizes the impact of reduced wing area. Raptors can have up to four primary moult centers in one wing.

Question 26

Secondaries

Answer 26

From 6 to 36 secondary feathers present.

Feathers closest to the body.

Question 27

Primaries

Answer 27

From 9 to 11 primary feathers present. Feathers are at the tips of the wings.

Question 28

Tail feathers

Answer 28

Tail feathers are usually replaced from the center outwards. But it is often more variable and there are some notable exceptions. Wood peckers moult central pair last due to structural importance.
Sequential ,out results in discrete plumage sequences.