Parental care in Hooded Plovers (Thinornis rubricollis)

Abstract

This paper examines the influence of stage of the reproductive cycle, age of eggs and chicks, size of clutches and broods, habitat and prevailing temperature on patterns of parental care in Hooded Plovers. To control for the influence of disturbance on parental care, data that represented a relatively low level of disturbance were chosen for analysis. ‘Activity scans’ were made every 5 min and recorded the activity of every bird in view. Attendance during laying (30.3% and 43.4% of scans, n = 2 nests) was lower than when the clutch was completed (90.9 ± 8.3% of scans, n = 14 nests); during laying, temperatures of model eggs varied with air temperature (n = 7 nests). Attendance at nests was uniformly high (68.4–98.6% of daylight time, n = 14 nests) across the incubation period but the average attendance in each hour of the day was negatively correlated with air temperature (slope of linear regression –0.02, P = 0.014, n = 14 nests). Absences from the nest when the incubator left of its own accord (voluntary absences) were longest at air temperatures of 15–19°C (14.4 ± 28.9 min, n = 103 absences). Voluntary absences were most frequent at times of day when egg temperatures came close to, and were moving towards, egg temperatures recorded under uninterrupted incubation. As chicks grew they were brooded less (slope of linear regression –0.02, P = 0.009, n = 12 broods), and diurnal brooding was not recorded among chicks more than 10 days old. The average time devoted to brooding was negatively correlated with air temperature (slope of linear regression –0.04, P < 0.001, n = 12 broods). Adults attended broods more closely than clutches (means of 1.8 and 1.5 parents in view per scan respectively); adults used distraction displays only when defending broods (62.1%) and not when defending clutches (n = 409 investigator approaches). Adults maintained body mass when incubating (98.4 ± 5.5 g, n = 44), but body mass decreased when attending chicks (92.2 ± 5.3 g, n = 10). This may be explained by decreased foraging time when rearing broods (0.1 ± 0.1% of scans cf. 13.8 ± 0.1% when incubating). This study reveals a high level of attendance of Hooded Plovers at their nests and broods. Parental care differs substantially between stages of the reproductive cycle, with ambient temperature an important influence on attendance during incubation and brood-rearing. Parental care changed with age of the brood but not with age of the eggs. A number of factors (clutch- and brood-size, habitat) did not affect parental care.