The effect of disturbance on the breeding biology of hooded plovers

© 2000 Dr. Michael A. WestonDisturbance of birds by humans is a growing problem. This thesis examines the mechanisms through which disturbance may reduce reproductive success in the Hooded Plover Thinornis rubricollis, a solitary-nesting shorebird for which disturbance is thought to constitute a conservation threat. As a precursor to examining disturbance in this species, breeding biology, life history and parental care were investigated in a colour-banded population of Hooded Plovers in coastal Victoria, Australia. Pairs bred in widely dispersed territories, and intact pairs bred in the same territories year after year. The breeding season was asynchronous and protracted, lasting up to eight months. Breeding success was low, but pairs re-nested frequently and rapidly after nest and brood failure, and sometimes after successfully fledging young. Survival of juveniles was similar to that reported for other plovers, and adult survival was high compared with other plovers. However, it was estimated that only 34% of adults were expected to live 11 years, the average period needed for a pair to replace itself (produce two young). One unusual feature of the life cycle of Hooded Plovers was the complete temporal overlap of adult wing moult with breeding. Complete biparental care occurred throughout the breeding cycle. There is some evidence that males undertook more of the nocturnal incubation while females undertook more of the diurnal incubation but overall, pair members shared incubation equally. Levels of incubation were high and constant over the incubation period. Once chicks hatched, the average number of parents nearby and the frequency of distraction displays increased. Additionally, adults fed less after their chicks hatched, and adult body mass decreased. Brooding decreased as chicks grew. A number of mechanisms through which disturbance could reduce reproductive success were examined. Disturbance resulted in egg temperatures moving above and below benchmark values, potentially leading to thermal stress in eggs. At least some recorded egg temperatures were potentially lethal. The proportion of abandoned eggs was highest in foredune nests, followed by beach then dune nests. This pattern mirrored the pattern of disruption of incubation by humans between habitats, suggesting thermal stress due to disturbance caused egg mortality. Thermal stress could also kill chicks, and disturbance disrupted brooding. Failure of adults to defend eggs or chicks due to disturbance did not lead to nest or brood failure. Adults defended nests and broods, but predation events were only observed during undisturbed conditions. For broods, foraging time decreased and the level of the habitat used for foraging changed with increasing levels of disturbance. Energetic stress is therefore another potential mechanism that could decrease chick survival. This study uncovered potential mechanisms through which disturbance could decrease hatching and fledging success in Hooded Plovers. Identification of the mechanisms through which disturbance acts, suggests that a management approach that emphasises managing the effect of disturbance rather than the response to it, will be a necessary component of the recovery of this species