Infanticide and Brood Reduction in Birds By Michael

Infanticide and Brood Reduction in Birds By: Michael Sweeney Ecol 484 2008

Infanticide? In Birds: Intentionally causing the death of an egg or nestling • Infanticide very common in birds. • Unlike mammals, birds employ behavior to their advantage. • Equally common among related birds and unrelated birds.

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 www. sialis. org

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 Danzenbaker Robert De. Candido

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 www. animalpicturesarchive. com • Mexican Jays, Acorn Woodpeckers www. freewebs. com www. ejphoto. com

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? www. avianweb. com David Faintich Facultative vs. Brood Reduction Obligate www. holdenby. com

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 Pelicaniformes Charadriiformes Anseriformes Podicepiformes Sphenisciformes Galliformes Ciconiiformes Falconiformes Gruiformes Columbiformes Cuculiformes Strigiformes Apodiformes Piciformes Passeriformes Facultative X X X X Obligate X X Passive X X X X Active X X X

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 Jody. Lee Red. Bull 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): 325 -332 Gill, 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. 10: 130