Many animals show multiple patterns of parental care, where more than one o
f the four basic patterns (biparental care, uniparental care by males or fe
males, or no care) is present within a single population during a single br
eeding season. We consider three reasons for the existence of multiple patt
erns of parental care: (1) mixed-strategy behaviours; (2) time-dependent be
haviour with parents changing their care decision during the breeding seaso
n; and (3) quality differences between individuals leading to different car
e decisions being made depending on the qualities of both parents. The basi
c framework we use to investigate these is a two-stage game-theoretical mod
el, and we highlight the importance of including feedback between the paren
tal care decisions made by population members and the probability that a de
serting individual will find a new mate. Including this feedback may introd
uce a nonlinear dependence of the fitness payoffs on the frequencies with w
hich the pure strategies ('care' and 'desert') are played by each of the se
xes. This can have important consequences for the existence of evolutionari
ly stable strategies (ESSs). For example, mixed-strategy ESSs may exist tan
outcome forbidden if the feedback is not included), and, in one model, the
feedback also prevents uniparental care by either sex from being evolution
arily stable. We also point out that decisions made by animals without depe
ndent offspring can have important consequences for observed parental care
behaviour. (C) 1999 The Association for the Study of Animal Behaviour.