Infanticide and Brood Reduction in BirdsInfanticide?Questions:Forms of InfanticideSlide 5Motives for Avian Infanticide: (Proximate Approach)Paternity Influenced InfanticideResource Influenced InfanticideSexually Selective InfanticideBrood Reduction (David Lack, 1947)Brood Reduction (cont’d)Slide 12Brood Reduction Across Avian OrdersTrends in Brood ReductionSlide 15Why Brood Reduction? (Ultimate Approach)ConclusionsAcknowledgementsInfanticide and Brood Infanticide and Brood Reduction in BirdsReduction in BirdsBy: Michael SweeneyEcol 4842008Infanticide?•Infanticide very common in birds.•Unlike mammals, birds employ behavior to their advantage.•Equally common among related birds and unrelated birds.In Birds: Intentionally causing the death of an egg or nestlingQuestions:•What forms of infanticide exist in birds?•What motives drive infanticide?•How does infanticide compare across taxa?•What ultimate reasons explain evolution of infanticide?Forms of Infanticide Parental vs. Non-parental infanticide – Egg vs. Hatchling destruction– Passive vs. Active infanticidewww.sialis.orgQuestions:•What forms of infanticide exist in birds?•What motives drive infanticide?•How does infanticide compare across taxa?•What ultimate reasons explain evolution of infanticide?Motives for Avian Infanticide: (Proximate Approach)•Paternity Influenced Infanticide•Resource Influenced Infanticide•Sexually Selective Infanticide• Brood ReductionPaternity Influenced InfanticidePaternity Influenced InfanticideA parent may kill young of different paternity, or even of questionable paternity.–Harem species•Bronze-winged Jacana ♀ –Monogamous species•Tropical House Wren•Palestine SunbirdMike Danzenbaker Robert DeCandidoResource Influenced InfanticideThe struggle for resources and opportunities are frequently motives for killing unrelated young .• Nest-site Limitations•Common; Tree Swallows, Starlings, Dippers• Mating Opportunity•Humboldt Penguins, Guira Cuckoos• Group Dominance•Mexican Jays, Acorn Woodpeckerswww.ejphoto.comwww.freewebs.comwww.animalpicturesarchive.comSexually Selective Infanticide Some parents will kill young in order to preferentially sire male or female offspring.Eclectus Parrot (Heinsohn, et al 1997). Encyclopedia Britannica OnlineBrood Reduction (David Lack, 1947)Parents may selectively starve young to reduce size of brood depending on environmental conditions.Core vs. Marginal offspring– Marginal offspring provide brood “insurance”• Allows equitable nest fitness if something happens to Core offspringOptimistic vs. Pessimistic Parenting?David Faintichwww.holdenby.comwww.avianweb.comFacultative vs. Obligate Brood ReductionBrood Reduction (cont’d)Parental Mechanisms of Brood ReductionActive:• Evicting/Killing marginal young• Starving marginal young through nepotism of larger and/or older young• Nest Desertion due to loss of core eggs/youngPassive:• Hatch order asynchronicity • Facilitating siblicide, or intentionally turning a ‘blind eye’Hatch order asynchronicityQuestions:•What forms of infanticide exist in birds?•What motives drive infanticide?•How does infanticide (Brood Reduction) compare across taxa?•What ultimate reasons explain evolution of infanticide?Brood Reduction Across Avian OrdersIncidence of Brood Reduction Types Across Avian OrdersFacultative Obligate Passive Active Pelicaniformes X X X XCharadriiformes X X XAnseriformes X X XPodicepiformes X X XSphenisciformes X X X XGalliformes X XCiconiiformes X X XFalconiformes X X X XGruiformes X X X XColumbiformes X XCuculiformes X X XStrigiformes X XApodiformes X XPiciformes X X XPasseriformes X X XTrends in Brood Reduction•Members of perhaps every bird order engage in some sort of facultative brood reduction.•Obligate brood reduction is common mostly in large birds.•Active brood reduction more prevalent in shore and water birds.•Relationship between altricial and precocial birds and forms of brood parasitism seems unclear.Questions:•What forms of infanticide exist in birds?•What motives drive infanticide?•How does infanticide (Brood Reduction) compare across taxa?•What ultimate reasons explain evolution of infanticide (Brood Reduction)?Why Brood Reduction? (Ultimate Approach)•Environmental Instability– Insufficient food availability•Physiological/Phylogenetic constraints–Ovulation speed/ timing.–Egg Size–Nutrient allocation limitations.Brood Reduction = Fitness Fail-safeConclusions•Numerous reasons motivate various types of infanticide in birds.•Birds seem to love infanticide, and when they don’t, they may encourage young to kill each other instead.•Parental Infanticide may be a useful ‘tool’ for maximizing yearly fitness.Acknowledgements•Becky Stephenson•Adam Radcliffe•Christine, Glenn and JodyLee•RedBullBrief List of Works CitedForbes, L.S. (1991) Insurance offspring and brood reduction in a variable environment: The costs and benefits of pessimism. Oikos. 62(3): 325-332Gill, Frank B. Ornithology: Second Edition. 1990. W.H. Freeman and Company: New York. Mock D.W. (1995) The evolution of parental optimism.Trends in Ecology & Evolution.