Male and female incubation in Pied Wagtails Motacilla alba: shared costs or increased parental care?

Abstrakti

The incubation behaviour of Pied Wagtails Motacilla alba was observed at six nests of monogamously and polygynously mated males. The proportion of time spent incubating by males varied markedly with mated status : polygynous males incubated less in total, in briefer sessions, or not at all. Polygynous females incubated for a greater proportion of the day than monogamous females . For assisted females, sessions preceding nest-relief by the male were shorter than sessions ending when the female left the nest unattended . When relieved by the male, females took longer recesses than in the male's absence; monogamous females lengthened their recesses more than the assisted polygynous female. Females lengthened their incubation sessions immediately after a recess during which the male incubated; the duration of female sessions following male-attended recesses correlated with recess length . The length of female sessions after a recess when the eggs were unattended did not vary with mated status or correlate with the preceding recess duration . Daily nest attendance was not correlated with temperature or rainfall for either sex. As a result of these varying incubation schedules, limited male incubation produced an increase in the proportion of the day the eggs were covered, whereas more extensive male incubation at monogamous nests produced both a greater increase in egg coverage and some reduction in the female's workload : male incubation in the Pied Wagtail thus primarily provides additional parental care .