Photo credit (C) Joseph Morlan
By why should a female, who can lay four eggs in a twosome without worrying about a nest mate tossing her eggs out, bother living in a foursome? The answer is that the larger group provides protection against egg predators.
Once loss of eggs to predators is taken into account, the starter in a foursome produces the most young, a female in a twosome produces an intermediate number of young, and the follower in a foursome the fewest. For the anis, the benefit from predator protection of living in extended families of two couples outweighs the disadvantages of a rancorous life at home.
“It’s a cooperative soft goth bird!” —RXS
Citations
S. Vehrencamp, 1978, The adaptive significance of communal nesting in groove-billed Anis, Behav. Ecol. Sociobiol. 4:1-33.
B.S. Bowen, R.R. Koford, and S.L. Vehrencamp, Breeding roles and pairing patterns within communal groups of groove-billed Anis, Anim. Behav. 34:347-66.
Roughgarden, J. (2013) Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press, Berkeley. p. 57-8.