Siblicide: An Introduction
Siblicide can be defined as the death of an individual due to the actions of a sibling. Siblicide can be caused by violent aggression such as pecking or eviction from the nest in birds or through physical attacks in mammals. Additionally, siblicide may be the result of starvation due to the aggressive exclusion from food by siblings. Many birds perform siblicide such as the cattle egret, brown booby, blue-footed booby, and the black eagle. Only a few species of mammals perform siblicide. A few of these species are the spotted hyena, domestic pig, and humans.
Cattle egrets live in relatively dry grasslands often near cattle or other large mammals in order to feed on invertebrates. These birds are ground nesters and nest in colonies. Although adult cattle egrets have relatively few predators, eggs and chicks are subject to predation from other birds or mammals. Also, chicks often die due to starvation.
In the cattle egret, parents do not interfere with sibling aggression. Parents do not keep their offspring from fighting with one another and allow some siblings to obtain more resources through sibling aggression. Moreover, parents act as facilitators by performing asynchronous hatching. Eggs are laid at different times and hatched days apart so that one chick always has a developmental advantage over its siblings.
When a parent’s reproductive fitness is impaired due to the death of an offspring, why do parents not intervene during bouts of sibling aggression? Additionally, why do parents even promote sibling aggression by asynchronous hatching or through hormones? Come up with some hypotheses to explain this apparent paradox.
From the point of view of the offspring: Why kill a brother or sister when it reduces your inclusive fitness? Come up with some hypotheses to explain this paradox.
Please send any comments, questions or suggestions regarding this website to Karen Hasty or Professor Verna Case.
This website was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2009.
[Drake et al., 2008; Fujioka, M., 1985; Hofer and East, 2008; Mock et al., 1990]