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Colonial Breeding

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

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  1. 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

  2. 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)

  3. 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

  4. Mating System Classification (Based on Pair Bonds) • 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

  5. Mating System Evolution • 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)

  6. Monogamy Rules in Birds • 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%)

  7. 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

  8. 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)

  9. 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

  10. 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)

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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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