Infanticide and Cannibalism

Infanticide without cannibalism is a behavior that has been widely described in numerous species (Glass 1985). Infanticide with cannibalism is considerably more rare but far from unheard of, having been reported in species such as lions, polar bears, and gulls (Elgar and Crespi, 331, 279).

Infanticidal lionTwo major benefits of infanticide have been suggested: increased nutrition and increased mating opportunities. In some amphibians, a cannibalistic diet has been associated with accelerated growth and higher survivorship (Elgar and Crespi 265). In times of food shortage, cannibalism may be the best option to ensure survival to the next reproduction. In the case of cannibalism of one's own offspring, increasing the nutrition of the parent may be an investment towards increasing future reproduction, at the cost of the current brood (Filial cannibalism is discussed in more detail in the section on oophagy). In some species, evidence exists that killing a female's current offspring can make her sexually receptive sooner than if she had raised those young (Glass, 1985). Lions and chimpanzees, for example, have been observed to kill juveniles and then mate with their mother (The Lion Research Center, Elgar and Crespi 331). The synthesis of these two explanations may help to account for situations in which infanticide is followed by cannibalism.  (For a video of male lion committing infanticide: ).

Oophagy and infanticide have been recorded in Color-banded 
Ring-billed gulls. Both males and females Ring-billed gullshave been observed consuming eggs or trespassing chicks of conspecifics, although it is more prevalent in males. Observations made by Brown and Lang showed that all cannibalized chicks brought to the nest were alive on arrival (1996). One dead chick was brought back to the nest but it was not eaten. They were also seen eating unguarded eggs at an adjacent nest. The results of Brown and Lang suggest that the only real selective advantage that could be gained by this behavior is the elimination of competitor genes, and even then it is a small contribution. Despite the lack of any large fitness advantage, cannibalism in these birds is prevalent, being the major cause of nest failure in some circumstances such as failed breeders and food shortages. Twenty to forty percent of the males observed in this study had cannibalistic behavior. Thus, these authors and previous researchers propose that most cannibalism events are carried out by only a few individuals with specialized behavior. (Brown and Lang, 1996)