Conference hears White-Bellied Sea-Eagle research
Three Kangaroo Islanders recently attended the Australasian Raptor Conference held at the Adelaide Zoo: David Irwin from Raptor Domain; Alastair Oakman from Southern Ocean Lodge, and District Ranger Caroline Paterson from Natural Resources Kangaroo Island.
Wildlife Consultant Terry Dennis, former District Ranger and long-time Kangaroo Island resident, presented his research findings ‘White-Bellied Sea-Eagle breeding refuge management in South Australia’s open coastal landscapes’.
Terry studied Sea-Eagle breeding behaviour and nest success on Kangaroo Island between 1985 and 1999. He reported significantly high levels of nest failure and low survival rates of young at the most disturbed nests.
Terry also surveyed the state’s coastal regions between 2008 and 2010 to identify the distribution and status of White-bellied Sea-Eagles (WBSE) as well as Eastern Osprey populations. He found South Australia’s WBSE to be between 70 and 80 pairs, with just 14 pairs on the mainland coast (which represented a decline of 20%).
Kangaroo Island has a significant population of 17 pairs, providing a stronghold for the endangered coastal raptors, but with increasing land development, tourism and other pressures, these iconic birds are threatened.
‘White-bellied Sea-Eagles are long-lived and form long-term breeding pairs. They have excellent vision and will fly from their nest (flush) as soon as disturbance is detected and stay away from the nest longer than other species,’ Terry said.
‘The pair will establish a guard-roost, where the non-attending bird will keep guard from a high vantage point, which may be up to 850 m from the nest. Disturbance to the guard-roost bird triggers the nesting bird to fly away from the nest as well’.
The absence of the parent bird has a critical impact on the survival of eggs and chicks. Parental absence for 20 minutes or more can result in the egg not developing. Eggs and chicks can also be killed by predators, suffer from heat stress, hypothermia or disturbance to their feeding cycles, which can have a serious effect on the chicks’ development. If disturbed during courtship or nest building, the pair may abandon their breeding attempt for the season.
‘Isolated nests are more likely to result in successful breeding compared with nest sites that have frequent disturbance. In most parts of Australia, WBSE nest in high trees or forests where they can tolerate a level of disturbance from below. However, in South Australia most nests occur on exposed cliffs and a single disturbance, particularly from above, can result in the birds abandoning their nest for the season’ Terry said.
With Kangaroo Island’s mostly low coastal vegetation it is important to avoid nests, wherever possible, for a distance of 2 km along the coast and 1 km inland from any known nesting areas during the breeding season.
The WBSE breeding season extends from May to December, so nesting is now well underway. The management actions taken by Natural Resources Kangaroo Island aim to minimise future disturbance to WBSE nesting sites, and are based on the findings and recommendations of scientific research.
All of us need to take the following actions wherever possible, to minimise disturbance to these iconic birds:
• if you see a White-bellied Sea-Eagle flush during the breeding season, move away by the fastest route
• plan activities and walks during the breeding season to be 2km from the coast and 1km inland from any known nest sites
• report any interference or deliberate disturbance to nests or White-bellied Sea-Eagles during the breeding season to Natural Resources Kangaroo Island.