The parental care regime of a population of socially monogamous Willie
Wagtails was studied over four breeding seasons in southern Victoria.
Incubation constancy was 95%, while brooding constancy was 82% early
in the nestling period, reducing to 29% later. Nestlings were fed on a
verage 8 times/h early and 12-14 times/h late in their development. Fa
ecal-sac removal occurred 2-3 times/h throughout the nestling period.
Territorial intrusions by conspecifics occurred on average less than o
nce/h, and those by potential predators about once/h; most elicited de
fensive responses from the territory-holders. Male and female partners
made equal contributions to most aspects of parental care behaviour;
however, females possibly predominated in the care of fledglings, whil
e their male partners initiated new nesting attempts. The magnitude -a
nd nature of male parental involvement was consistent with an evolutio
nary link between biparentalism and social monogamy.