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Matt Johnson
HSU Wildlife 365
Ornithology
ORNITHOLOGY
(Humboldt State Univ. WILDLIFE 365)
LECTURE 20 – MATING SYSTEMS I
I.
II.
Introduction.
Types of mating systems.
1. Monogamy (single marriage). Occurs in about 91% of all bird species.
Here, there are prolonged more or less exclusive pair bonds between
single members of the opposite sex for the purpose of raising young.
a. Some birds form life-long monogamous bonds (e.g., swans).
b. Others are only monogamous within a breeding season; mating with
different individuals most years (e.g., many songbirds).
2. Polygamy (many marriage). Occurs in about 3% of all bird species.
Any mating system involving multiple pair bonds. There are three
kinds of polygamy.
a. Polygyny (many woman). Occurs in about 2% of all bird species.
That kind of polygamy in which a male mates with two or more
females, who each mate usually with only one male. This can only
occur if not all males mate. Thus, in polygynous mating systems,
the breeding success of males varies much more than does that of
females.
b. Polyandry (many man). Occurs in about 1 percent of all bird
species. That kind of polygamy in which a single females mates
with many males, each of which only mates with a single female.
The male usually tends the clutch of eggs. Here, not all females
reproduce, and therefore there is more variation in female breeding
success than in male breeding success.
i.
If the female lays a full clutch of eggs with a mate, then
moves on and does it again and again with more mates, it's
called serial polyandry.
ii.
If she has two or mates at once it is called simultaneous
polyandry.
c. Polygynandry (many woman man). Occurs in only a few taxa -especially the ratites. That kind of polygamy in which a female
mates with several males, each of which also mate with several
females. In the ratites, a single male will tend of clutch of many,
many eggs, which are laid by several females who he attracts to his
nest....and these females then move on to deposit eggs in successive
males' nests. It can be distinguished from promiscuity by mutual
courtship, mutual mate selection.
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III.
3. Promiscuity (pro- miscere to mix). Occurs in about 6% of all bird
species. This is described as indiscriminant sexual relationships -- no
prolonged pair bonds formed. Seen in hummingbirds and most grouse,
where a male displays and mates with receptive females, who then go
on to mate with other males. Males display indiscriminately to all
watching females. Variance in male reproductive success reaches its
maximum value in this mating system. Intense competition for mating
opportunities, and intense sperm competition.
Monogamy.
A. Monogamy evolves presumably because a pair of birds can successfully
raise more young than can a female without a mate. So it behooves
both sexes to cooperate, or neither will pass on very many genes to the
next generation.
B. Pair formation and assessment.
1. Obviously, in most mating systems, the females are the focus -they are the ones laying the eggs, doing much of the incubation, etc.
Their role in parenting is critical to the survival of the young. But
in monogamous birds, the roles of males are often very important as
well.
a. Thus, females must choose mates very carefully -- their choice
affects their own reproductive success.
b. As a consequence, any ornamentation or display a male may
have that indicates or advertises his ability to care for young
will be favored by sexual selection.
c. Indeed, females respond to a variety of "cues" of male quality.
We talked a lot about plumage and song cues such as long tails
or large song repertoires....but other indicators exist as well,
such as courtship feeding.
2. Courtship feeding.
a. Courtship feeding is not only a ritualized display - it can
significantly increase a female's energetic intake.
b. The more a male feeds his mate, the more likely those eggs will
be produced early, and the more likely they will be large in size
and number.
c. Males can provide up to 40% of a females' energy, especially
during incubation, when she needs to stay on the nest the
longest.
d. Male Blue Tits are perhaps the champion courtship feeders.
Over 1000 trips per day while the female is incubating -- that's a
trip a minute for 17 hrs straight every day!
e. Thus, a female will often "judge" a prospective mate by his
ability to bring her food before they reproduce.