Parental care patterns differ enormously among and even within species. In Chinese penduline tits (Remiz pendulinus), for example, biparental care, female-only care, male-only care, and biparental desertion all occur in the same population; moreover, the distribution of care patterns differs systematically between populations. By means of an individual-based model, we show that such diversity can readily evolve. We report five main findings. First, under a broad range of parameters, different care patterns (e.g. male care and biparental care) coexist at equilibrium. Second, for many parameters, alternative evolutionary outcomes are possible; this can explain differences in care patterns across populations. Third, rapid evolutionary transitions can occur between alternative equilibria; this can explain the often-reported evolutionary lability of parental care patterns. Fourth, season length has a strong but non-monotonic effect on the evolved care patterns. Fifth, when uniparental care efficiency is low, biparental care tends to evolve; however, in many scenarios uniparental care is still common at equilibrium. Our study sheds new light on Triver’s hypothesis that the sex with the highest pre-zygotic investment is predestined to invest a lot post-zygotically as well. We also discuss the implications of climate change, which simultaneously affects season length and efficiency of parental care.