Infanticide and Brood Reduction in Birds By: Michael Sweeney Ecol

Infanticide? 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 nestling

Questions: 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 infanticide

Questions: 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 Reduction

Paternity Influenced Infanticide A parent may kill young of different paternity, or even of questionable paternity. –Harem species Bronze-winged Jacana ♀ –Monogamous species Tropical House Wren Palestine Sunbird Mike DanzenbakerRobert DeCandido

Resource Influenced Infanticide The 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 Woodpeckers

Sexually Selective Infanticide Some parents will kill young in order to preferentially sire male or female offspring. Eclectus Parrot (Heinsohn, et al 1997). Encyclopedia Britannica Online

Brood 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 offspring Optimistic vs. Pessimistic Parenting? David Faintich Facultative vs. Obligate Brood Reduction

Brood Reduction (cont’d) Parental Mechanisms of Brood Reduction Active: Evicting/Killing marginal young Starving marginal young through nepotism of larger and/or older young Nest Desertion due to loss of core eggs/young Passive: Hatch order asynchronicity Facilitating siblicide, or intentionally turning a ‘blind eye’ Hatch order asynchronicity

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 Across Avian Orders Incidence of Brood Reduction Types Across Avian Orders Facultative Obligate Passive Active PelicaniformesXXXX CharadriiformesXXX AnseriformesXXX PodicepiformesXXX SphenisciformesXXXX GalliformesXX CiconiiformesXXX FalconiformesXXXX GruiformesXXXX ColumbiformesXX CuculiformesXXX StrigiformesXX ApodiformesXX PiciformesXXX PasseriformesXXX

Trends 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-safe

Conclusions 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 RedBull Brief List of Works Cited Forbes, L.S. (1991) Insurance offspring and brood reduction in a variable environment: The costs and benefits of pessimism. Oikos. 62(3): Gill, Frank B. Ornithology: Second Edition W.H. Freeman and Company: New York. Mock D.W. (1995) The evolution of parental optimism. Trends in Ecology & Evolution. 10:130