Colonial Breeding

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Colonial Breeding

• Occurs species feed in intraspecific flocks on
  unpredictable foods
• Fish-eaters herons, seabirds
• Aerial insectivores bee-eaters, swifts, swallows
• Some seed-eaters weaverbirds
• Key benefit locating food through information
  center
• No other feeding benefits

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Anti-predator Benefits

• Confuse predator no
• Detection of predators no
• Danger to predator moderate benefit
• Works against birds, not mammals
• Safety in numbers moderate benefit
• Shielding benefit for some (dominants in
  center), not others (subordinates periphery)

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Constraint of limited nest sites may contribute
to coloniality

• Safe places to nest near food source may be
  limited, clumped in space
• Safe place necessary to overcome cost of having
  nests in close proximity

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Mating System Classification (Based on Pair Bonds)

• Monogamy each individual has 1 bond
• Polygamy some individuals have gt1 bond
• Polygyny males have gt1 bond
• Polyandry females have gt1 bond
• Polybrachygamy both males and females have gt1
  bond

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Mating System Evolution

• Monogamy evolves if x gt p(yz) (1-p)y
• Affected by value of (male) parental care,
  difference in number of young 2 parents can raise
  (x) relative to number 1 parent can (y)
• Affected by probability of obtaining an
  additional mate (p)
• Usually males rather than females are polygamous
  (eggs cost more than sperm)

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Monogamy Rules in Birds

• Monogamy is more common in birds than in any
  other kind of animal
• gt90 of bird species are monogamous
• Large contribution of 2nd parent due to advanced
  behavioral forms of parental care that can be
  performed by both sexes
• Feeding young and especially incubation
• (x-y) large, y may be 0
• Polygamy more common in species that do not feed
  young (17 vs 7)

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Complications

• The duration of the pair bond varies from
  perennial to annual
• Divorce occurs, often in response to
  unsuccessful breeding at young ages
• Extra-pair copulations are common, with 30-50 of
  the young in the nest being sired by an
  extra-pair male in some species

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Resource Defense Polygyny

• 2nd most common mating system in birds
• Male obtains additional mates (high p) by
  controlling resources valuable to females
• Honeyguide males defend bee nests, hummingbird
  males defend patches flowers (provide no parental
  care)
• Polygyny threshold model territories vary
  greatly in quality, multiple females on best
  territories (Red-winged Blackbird)

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• Resource defense polygyny occurs in several
  species in productive temperate habitats
  (grasslands, marshes)
• Lots of variation in number of mates in some
  species (1-15 in Red-winged Blackbirds), only a
  little in others (a few males have 2 mates rather
  than 1)
• 5 rule distinguishes resource defense polygyny
  from monogamy
• Extra-pair copulations occur

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Male Dominance Polygyny

• Males defend mating territories
• Territories may be highly clumped on leks or more
  spread out in exploded leks
• Leks in open areas (sage grouse), exploded leks
  in forest (ruffed grouse)
• Females visit lek to choose a mate
• (x-y) small due to food type, no male care, no
  resources for males to defend
• Occurs in fruit-eaters (cotingids, manakins,
  bowerbirds, birds-of-paradise), species that do
  not feed young (grouse, shorebirds)

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Female Defense Polygyny

• Male defends group of females (high p)
• Rare because females do not travel in groups when
  nesting (common mammals)
• Restricted to a few pheasants, the odd systems of
  rheas and tinamous that also involve sequential
  polyandry
• Groups of females lay eggs in a succession of
  nests cared for by individual males

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Rapid Multiple Clutch Polygamy

• Occurs in a few shorebirds (sanderling), button
  quail (Gruiformes)
• High nest predation, male cares for first clutch
  to free female to feed to produce a replacement
  clutch
• Female cares for 2nd clutch if first survives
• Polyandry occurs when female gives 2nd clutch to
  new male, produces 3rd for herself

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Other Types of Polyandry

• Also restricted to shorebirds, Gruiformes
• Associated with development of male care, female
  now has option to invest in young from first bond
  or seek additional mates
• Not clear why male care evolved

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Resource defense polyandry in jacanas, Spotted
Sandpipers, a few Gruiformes

• Now polyandry (rather than polygyny) threshold
  model applies, females defend territories that
  attract multiple males, males care for eggs and
  young

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Female Access Polyandry

• Counterpart to leks, females court males at a
  central location
• Females produce a clutch for which male cares,
  then return to courting area to seek an
  additional mate
• High p (excess males available) drives evolution
  of this system
• Found in phalaropes

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