Birds – Part V

VERTEBRATE ZOOLOGY (VZ Lecture27 – Spring 2012 Althoff - reference PJH Chapters 16-17)

Bill Horn

Mating Systems

• Considerable variety in pair bonds for birds—ranging from brief sexual union to sustained mutual efforts:

1) monogamy – “mono” + “marriage”2) polygamy – “many” + “marriage”3) polygyny – “many” + “woman”4) polyandry – “many” + “man”5) polgynandry – “many” + “woman” +

“man” 6) promiscuity – “pro” + “mix”

Greek for…

Mating Systems Largely Driven by Coloration and Vocalizations

• Typically, males more colorful than males• Combination of coloration and vocalizations result

in breeding displays…much variety across the class Aves

• “Experience” matters…as older males tend to be have better songs than young males

• Color “quality” and “quantity” ….and size influences rate of breeding opportunities

• Note: _____ – breeding/mating vocalizations vs._____ - feeding, begging, alarm, flock

communication

Monogamy

• “the” predominant avian mating system• _____ of bird species (but % probably continuing

to _____ because of DNA evidence on paternal “contributions” to clutches…suggesting promiscuity)

• Prolonged and essentially exclusive bond with a single member of the opposite sex for purposes of raising young.

• Appears common among passerines, raptors (hawks and owls)

F + M

Polygamy

• Any mating system involving pair bonds with multiple mates of the opposite sex

• These are all “subsets” of the polygamy category:

F + M.…MM + F...F

Polygyny Polyandry Polygyandry

Polygyny

• _____ of bird species (but % probably continuing to _______ because of DNA evidence on paternal “contributions” to clutches that we originally thought had monogamous status)

• Male pairs with 2 or more females (bigamy if M with 2 F).

• Sustained association with the females (pre- and post-copulation) separates this from promiscuity

• Example: red-winged blackbirds • ______________ polygyny male controls

access to critical resource like nesting habitat and/or food resources. More common where “patchy” distributions of these resources

M + F…F

Polygyny..con’t

• ______________ polygyny—males are not defending females nor are they defending a resource. Instead, males compete for females by establishing “dominance” or by demonstrating their quality through displays.

Aggregations of many males in a small area are called ______

ex. prairie chickens

sage grousesharp-tailed grouse

Leks…what favored evolution of this approach to breeding? A couple of hypotheses…

• Hot ______ —males gather at a location where they are most likely to encounter roaming females. Gives male(s) a chance to establish strategic position (usually center of lek) to convey dominance

• Hot ______ —females can go to a group display which facilitates comparisons which male is the “best”/most fit is more easily determined. Assessment can be made more rapidly (in a few minutes, even) than if she had to visit each males with territories scattered across a landscape

AFRICAN LONG-TAILED WIDOWBIRD

Polyandry

• ______ of bird species • Female pairs with 2 or more males • Sustained association with the males (pre- and post-

copulation to varying degrees) • Males tend to the clutch, stay with hatchlings• Females tend to be more brightly colored than males• Examples: phalaropes, spotted sandpipers• _____________ polyandry female controls access

to critical resource like nesting habitat and/or food resources. More common where “patchy” distributions of these resources. Clutch sizes usually small

F + M…M

Wilson’s phalaropes

Polyandry…con’t

• ___________ polyandry – female lays full clutches of eggs for successive mates…thus, incubation of eggs/nests are not essentially overlapping. Advantage: __________________________

vs.

• ____________ polyandry – female lays full clutches of eggs for two or more mates during the same time period…thus, incubation of eggs/nests are essentially overlapping. Advantage: ___________________________

Polygynandry

• _____ of bird species• Female pairs with several males, each of which

also pairs with several different females• Common among the tinamous, the flightless ratites

(ostrich, rheas, emu), and some songbirds (Smith’s longspur and hedge accentors)

• Among ratites and tinamous, males incubate mixed clutches of eggs from several different females which deposit eggs successively with different males

F1 + M1, F1 + M3, F2 + M1 etc.

Promiscuity

• _____ of bird species• Indiscriminant sexual relationships—usually of

______ duration

• Examples: male hummingbirds and male manakins (…and technically, one could classify grouse species—lek or non-lek like the ruffed grouse found locally as promiscuous)

Promiscuity…con’t

• Advantage for ______:1) chance to “spread” genes around with

multiple females (not all “genes” in one basket, so-to-speak )

2) can sire more offspring in a single breeding season

3) not all his eggs in one nest…so if predator takes out one nest, he still may end up siring offpspring that breeding season

Promiscuity…con’t

• Apparent advantages for ________:

1) Some males are more fertile than others, so reduce risk of incubating infertile eggs

2) “_________” hypothesis: female increases fitness of her male offspring by mating with a male who has especially attractive ____________ characteristics

Egg laying & Nesting/Parental Care

• Nest preparation variable, ranging from…a) no nest (just “lay” eggs) (ex. Nighthawks,

fairy tern)b) scrap (ex. gulls)c) scarp and line (ex. piping plovers, killdeer)d) “build” a nest (most common)e) “weave” a nest (ex. weaverbirds, orioles)f) “build up” (many years, in some cases…

ex. eagles, hawks)• Value of nest with respect to incubation of eggs:

a) ______ provided for developmentb) __________ to many predators

Oviparity

• Considering the diversity of birds…including a wide variety of mating strategies….all are limited to laying eggs

• All lay a single egg laid at a time (usually 24-36 hours between eggs). Contrast this to viviparity in lizards and snakes….multiple eggs are retained in the oviducts of the female for extended (>24-36 hr) periods of time. The strategy of viviparity suggest that for this group of vertebrates, the benefit of egg __________ outweighs its cost (makes sense in “cold climates”—eggs can start to

develop sooner). Vice versa with respect to birds…laying one egg per day, then incubating them all must outweigh the cost.

Fig. 17-29 p473, PJH

• Site of fertilization

• Albumen and shell membranes (not shell) are secreted

• Egg enclosed in calcareous shell

• Deposited

12

3

4

ovary infundibulum

shell gland

cloaca

Different patterns of Laying Eggs• Some species are ______________ layers:

a) a fixed number of eggs are laidb) usually those species that have

1, 2, 3, 4, or 5 eggs for an averageclutch size.

c) remove and egg and they probably won’t lay a “replacement” egg

d) example: piping plover• Some species are ______________ layers:

a) not usually a “fixed” number of eggsb) usually those species that have

10 or more eggs for a clutchc) remove an egg or eggs and they just

keep laying (example: chicken)

Different patterns of Incubating Eggs• Some species start to incubate eggs after 1-2 are

laid even if clutch ends up being 3-5 or more eggsex. Most raptors (hawks and owls)….results

in _______________ hatching of young

advantage? ______________________• Some species do not start incubation until all eggs in

the clutch are laid. Common among species with small clutches (i.e., 2-5) and large clutches

Results in ______________ hatching of young

advantage? _______________________

The Egg• Inorganic part of the eggshell contains about 98%

crystalline calcite (CaCO3)…and the embryo obtains about _____ of its calcium from the egg shell.

• Two shell membranes are secreted to enclose the yolk and albumen: a) “outer” shell membrane b) “inner” shell membrane…..

…as these membranes are laid down, H2O and carbohydrates are added to the albumen via active transport of Na & osmotic flow of H20.

• Mammillary bodies are sites of calcite crystal forming

Fig. 17-31 p474, PJH

Mammilary core

Outer shell

membrane

inner shell

membrane

chorioallantoic

membrane

embryo

The Egg…con’t• Changes in fluid concentrations surrounding the egg

change as the shell is put down, with increased concentrations of Mg and P…and a pattern in the change of crysallization in the surfaced layers of the shell (Fig. 17-

30, p474 PJH).

• In “end” product, pores are present that allow O2 and CO2 to diffuse in and out, respectively. Pores represent about 0.02% of the surface of the eggshell

• _______________ membrane serves for gas exchange until 1-2 days before hatching. Air cell at the blunt end of the egg is punctured by about to hatch chick and ventilation of lungs takes over gas exchange

• Egg tooth helps chick “saw” its way out!

Fig. 17-31 p474, PJH

chorioallantoic

membrane

Pores—not all are ‘straight’

zona pellucida

“Evidence” for

__________________