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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Colonial breeding l.jpg
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) coloniality

  • Monogamy: each individual has 1 bond

  • Polygamy: some individuals have >1 bond

    • Polygyny: males have >1 bond

    • Polyandry: females have >1 bond

    • Polybrachygamy: both males and females have >1 bond

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Mating System Evolution coloniality

  • Monogamy evolves if x > p(y+z) + (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 coloniality

  • Monogamy is more common in birds than in any other kind of animal

  • >90% 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 coloniality

  • 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 coloniality

  • 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 productive temperate habitats (grasslands, marshes)

  • 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 productive temperate habitats (grasslands, marshes)

  • 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 productive temperate habitats (grasslands, marshes)

  • 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 productive temperate habitats (grasslands, marshes)

  • 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 few Gruiformes

  • 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