The IEH states that the extra egg(s) produced by the parent serves as an 'insurance policy' in the case of the failure of the first egg (either it did not hatch or the chick died soon after hatching). Originally proposed by Dorward (1962), the insurance egg hypothesis (IEH) has quickly become the most widely supported explanation for avian siblicide as well as the overproduction of eggs in siblicidal birds. By letting the offspring kill each other, it saves the parents time and energy that would be wasted on feeding offspring that most likely would not survive anyway.

If resources are scarce, the parents may encourage siblicide because only some offspring will survive anyway, so they want the strongest offspring to survive. Some parents encourage siblicide, while others prevent it. It is also somewhat advantageous for the parents because the surviving offspring most likely have the strongest genes, and therefore likely have the highest fitness. Siblicide is advantageous for the surviving offspring because they have now eliminated most or all of their competition. Siblicide generally only occurs when resources, specifically food sources, are scarce. This is perhaps because siblicide takes a great amount of energy and is not always advantageous. More birds are facultatively siblicidal than obligatory siblicidal. For instance, in the blue-footed booby, a sibling may be hit by a nest mate only once a day for a couple of weeks and then attacked at random, leading to its death. In facultative siblicidal animals, fighting is frequent, but does not always lead to death of a sibling this type of behavior often exists in patterns for different species. In birds, obligate siblicidal behavior results in the older chick killing the other chick(s). Facultative siblicide means that siblicide may or may not occur, based on environmental conditions. Obligate siblicide is when a sibling almost always ends up being killed. Siblicidal behavior can be either obligate or facultative. (The word is also used as a unifying term for fratricide and sororicide in the human species unlike these more specific terms, it leaves the sex of the victim unspecified.) Siblicide has mainly, but not only, been observed in birds.

It may occur directly between siblings or be mediated by the parents, and is driven by the direct fitness benefits to the perpetrator and sometimes its parents. Braun) is the killing of an infant individual by its close relatives (full or half siblings). Siblicide (attributed by behavioural ecologist Doug Mock to Barbara M.

When the second egg hatches, any siblings present will almost certainly kill their younger brother or sister. A Nazca booby ( Sula granti) with a chick and egg.

Blue footed boobies reading with answer