Infanticide is surprisingly widespread in the animal kingdom, leading
scientists to look for an evolutionary explanation of the
behavior...that is, in what way might infanticide e considered
"adaptive" or advantageous to an individual animal, or to an animal
population as a whole.
The so-called sexual selection hypothesis is the prevailing
explanation of some forms of infanticide, as described here:
Infanticide by Males and its Implications
...known as the sexual selection hypothesis, this idea proposes that a
male increases his reproductive success by killing unrelated dependent
infants if the infant?s death makes the female return to receptivity
sooner than would otherwise have been the case and if he has a higher
probability of siring her next offspring...
In other words, if males kill off unrelated infants, it frees the
female from the demands of mothering, and leaves her ready at an
earlier date to have more children, presumably carrying the genes of
the male who did the deed in the first place.
In squirrels, the adaptive dynamics are not as clear-cut, at least
according to the site I referred to earlier:
[for the case of an unrelated male killing an infant]...Sherman
hypothesizes that males will do this to grow stronger and gain weight
at a higher rate in order to win more females during the next breeding
[For females it's a different adaptive dynamic at work] Sherman
suggests that females practice infanticide to eliminate competition
for nest burrows.
These are all merely hypotheses -- best guesses based on the evidence
at hand -- and are certainly not to be taken as definitive. Still,
they suggest an adaptive rationale underlying an otherwise very
difficult-to-explain (and rather bizarre) behavior.
Hope that helps, but if you need any more information, just let me know.
search strategy -- Google searches on: