siblicidal

In this latter case, the elder sibling will usually become aggressive and siblicidal.

Furthermore, the parents actually try to suppress the siblicidal behavior, rather than ignoring or encouraging it.

Siblicidal behavior can be either obligate or facultative.

However, unlike the obligately siblicidal masked and Nazca booby chicks, their behavior is not always lethal.

In birds, obligate siblicidal behavior results in the older chick killing the other chick(s).

Facultatively siblicidal blue-footed booby A-chicks only kill their nest mate(s) when necessary.

For instance, spotted hyenas (Crocuta crocuta) have been known to exhibit facultative siblicidal behavior.

Blue-footed booby parents, meanwhile, build nests with steeper sides, thus preventing some older chicks from engaging in siblicidal behaviour.

When both cubs were alive, total maternal input in siblicidal litters was significantly lower than in non-siblicidal litters.

More birds are facultatively siblicidal than obligatory siblicidal.

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.

Siblicidal "survival of the fittest" is also exhibited in parasitic wasps, which lay multiple eggs in a host, after which the strongest larva kills its rival sibling.

The closely related masked and Nazca boobies are both obligately siblicidal species, while the blue-footed booby is a facultatively siblicidal species.

Obligately siblicidal masked and Nazca booby A-chicks kill their sibling no matter if resources are plentiful or not; in other words, siblicidal behavior occurs independently of environmental factors.

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.

When non-obligate siblicidal blue-footed boobies were swapped with obligate siblicidal masked booby chicks, it was found that the blue-footed chicks exhibited more siblicidal behavior.

In a facultatively siblicidal species, aggression occurs between siblings but is not always lethal, whereas in an obligately siblicidal species, aggression between siblings always leads to the death of one of the offspring.