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 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 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 (contd) 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 Pelicaniformes X X X X Charadriiformes X X X Anseriformes X
X X Podicepiformes X X X Sphenisciformes X X X X Galliformes X X Ciconiiformes
X X X Falconiformes X X X X Gruiformes X X X X Columbiformes X
X Cuculiformes X X X Strigiformes X X Apodiformes X X Piciformes X X X
Passeriformes 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 dont, 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): 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
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