Distribution and Status of White-Bellied Sea-Eagle, Haliaeetus Leucogaster, and Eastern Osprey, Pandion Cristatus, Populations in South Australia T
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March 2011 1 Distribution and status of White-bellied Sea-Eagle, Haliaeetus leucogaster, and Eastern Osprey, Pandion cristatus, populations in South Australia T. E. DENNIS, S. A. DETMAR, A. V. BROOkS AND H. M. DENNIS. Abstract Surveys throughout coastal regions and in the INTRODUCTION Riverland of South Australia over three breeding seasons between May 2008 and October 2010, Top-order predators, such as the White-bellied estimated the population of White-bellied Sea- Sea-Eagle, Haliaeetus leucogaster, and Eastern Eagle, Haliaeetus leucogaster, as 70 to 80 pairs Osprey, Pandion cristatus, are recognised and Eastern Osprey, Pandion cristatus, as 55 to indicator species by which to measure 65 pairs. Compared to former surveys these data wilderness quality and environmental integrity suggest a 21.7% decline in the White-bellied Sea- in a rapidly changing world (Newton 1979). In Eagle population and an 18.3% decline for Eastern South Australia (SA) both species have small Osprey over former mainland habitats. Most (79.2%) populations with evidence of recent declines sea-eagle territories were based on offshore islands linked to increasing human activity in coastal including Kangaroo Island, while most (60.3%) areas (Dennis 2004; Dennis et al. 2011 in press). osprey territories were on the mainland and near- A survey of the sea-eagle population in the shore islets or reefs. The majority of territories were mid 1990s found evidence for a decline in the in the west of the State and on Kangaroo Island, with breeding range since European colonisation three sub-regions identified as retaining significant (Dennis and Lashmar 1996). Similarly, a survey habitat for both species. These were upper-western of of the opsrey population in 2005, reported Eyre Peninsula, southern Eyre Peninsula and high levels of nest failure in some areas (Dennis Kangaroo Island (Figs. 4 & 7), which together 2007a). encompassed 70.8% of the White-bellied Sea-Eagle territories and 62.1% of Eastern Osprey territories. These populations are somewhat isolated from Threats identified for both species included: rural those in other regions of Australia, with the most land-use change leading to increased human activity westerly sea-eagle territory in SA >400 km from in the coastal landscape and corresponding levels of the nearest known territory in Western Australia disturbance at nest sites; poorly conceived tourism (WA) and the most easterly coastal territory (on developments; ill-timed research projects and pest the Fleurieu Peninsula) >550 km from the nearest plant control programs coincident with the breeding known territory in Victoria at Lake Connewarre season; and inter-species conflicts between White- (Dennis and Lashmar 1996). They are capable of bellied Sea-Eagles with Wedge-tailed Eagles, Aquila long distance movement, for example a nestling audax, were identified. Collectively, these habitat banded at Franklin Harbour on Eyre Peninsula in degrading processes and threats have reduced the 1970 was found dead on Fraser Island Queensland wilderness quality and therefore the breeding refugia, the following year (Aust. Bird Bander 10: 82), and particularly for the disturbance-intolerant White- it is likely that the Murray River system is a bellied Sea-Eagle. conduit for genetic exchange as there are breeding territories thinly distributed along the river in each State (Marchant and Higgins 1993). 2 South Australian Ornithologist 37 (1) Similarly, with ospreys there is also a substantial Sea-Eagle and Eastern Osprey in SA; ii) locate break in their continental distribution, with significant habitats; and iii) identify adverse the most westerly territory on the Bunda Cliffs human activities and habitat threats. >750 km from the nearest known territory near Esperance in WA, and there are no recent or historical breeding records south-east of METHODS Kangaroo Island in SA, or from Victoria or Tasmania (Dennis 2007a). Raptor populations are determined by surveying the number of territorial or breeding In contrast to the forested habitat available pairs in suitable habitat (Newton 1979). Both the in other States, in SA both species are largely sea-eagle and osprey form long-term pairs and limited to offshore islands or remote coastal cliff are known to use nesting locations over long sites and associated broken terrain with low time periods, with favoured sites being used by heath vegetation cover, and tree nests are rare. successive generations (Marchant and Higgins This results in most breeding sites having little 1993; Clunie 2003; Dennis 2007b; Dennis et al. in visual screening and therefore being particularly press). Therefore, relative stability was assumed vulnerable to disturbance from human activity, for previously known sites in remote locations which invariably occurs above nest level and enabling survey effort to be targeted in those in line-of-sight at long distance from the nest areas and prospecting surveys to concentrate or guard-roost sites (Olsen 1998, Dennis et al. in on potential and previously poorly surveyed press). sections of coastline. In 2008 the conservation status of both species Survey scope and planning was elevated to Endangered in SA. Both are listed Prior to on-ground survey, digitised oblique on the Marine and Migratory Species Schedules imagery and orthorectified aerial imagery from of the Federal Environment Protection and the Department for Environment and Natural Biodiversity Conservation Act, 1999. Resources (DENR) were examined for terrain With support from various sources a series features typical of those used as breeding sites, of surveys commenced in 2008 to re-assess in order to plan access and survey methods what was known of these species in SA. The in unfamiliar areas. Between June 2008 and aim of these surveys was to: i) determine the October 2010 strategic coastal surveys were distribution and status of the White-bellied conducted over three breeding seasons between Figure 1. The likely phases of greatest sensitivity and corresponding risk of nest desertion during the White-bellied Sea-Eagle breeding season in South Australia. Note the risk of desertion increases through the courtship phase, is highest from mid-June to mid-September, and declines with increased parental investment thereafter. This figure adapted from estimates developed in Tasmania (Mooney and Holdsworth 1991; Forest Practices Authority 2006). March 2011 3 Wilson Bluff on the WA border (2008) and transects were conducted where vehicle access Rivoli Bay in the South East of SA (2010), in the to survey sites was not possible or ethical. Riverland between Morgan and the New South Access to DENR Reserves was under Scientific Wales Border (2009-10), and in offshore island Permit (C25629 1-3), entry to the Yalata groups off Yorke and Eyre Peninsulas (2010). Indigenous Protected Area was through the In addition, a comprehensive literature search Yalata Community Council, and considerable at the South Australian Museum (SAM) and effort was directed to obtaining permission to Royal Geographic Society of SA libraries, found access private property. historical records of breeding locations for both species. Due to the remoteness of some sections of coastline volunteer back-up assistance was Minimising disturbance essential to maintain portable radio contact, Due to the sensitivity of sea-eagles to mobile or satellite phone watch and to ferry a disturbance during the breeding season vehicle between the commencement and end (Olsen 1998; Clunie 2003; Threatened Species point of foot transects. Section 2006; Dennis et al. in press), ground surveys were confined to mid-September Vessel-based surveys and October, when pairs were settled into Remote coastlines were surveyed from the sea. established patterns of foraging forays and nest These included: 55 km of coast south of Elliston protection, thus avoiding the risk of desertion on western Eyre Peninsula; most of Kangaroo during the courtship, pre-egg laying and early Island; Nuyts Archipelago; and the Investigator, incubation phase in May to early September Gambier and Sir Joseph Banks Groups of (Figure 1). Depending on terrain limitations, islands. observations were made at distances of at least 750m from sea-eagle nest sites and 250m from Near-shore islands (<4 km offshore) were osprey sites using high-resolution binoculars surveyed visually by spotting scope from (Swarovski 8.5 X 42 and 2 X booster) and/or a the nearest headland vantage point, or by tripod mounted spotting scope (Kowa 25, 40 circumnavigation by small boat. A canoe or and 60 X 75). However, because of familiarity dinghy was used to survey tidal creeks in with terrain and nest locations from previous mangrove forest areas, and for lagoons and surveys, some territories could be surveyed at subsidiary creeks in the upper-Murray and lesser distance without causing disturbance. Bookmark-Chowilla floodplain complex. Similarly, as sea-eagles largely ignore boats that are >150 m away, sea-based surveys were able Data processing and storage to be undertaken during the sensitive breeding A standardised data-sheet was used for each season onset in May and June, when all pairs site throughout the project. Once identified by spend long periods at the nest engrossed in ground or vessel-based survey, the location of courtship and nest repair activity, regardless of nest sites was tentatively determined using a whether egg laying occurs. In contrast, ospreys range-finder (Leupold RX-IV 8 X 28) to measure are strongly attached to nest sites throughout an offset distance (accuracy ± 5 m) along a the year and are generally more tolerant to compass bearing from a GPS (Garmin 60CSx) approach from landward. determined waypoint location. At some inactive sites it was possible to obtain location data Ground surveys directly above a cliff nest or directly under a Ground surveys were conducted by a nest tree. All observation data were entered in combination of vehicle and foot traverse e.g. a field notebook or directly onto survey record in the Far West region in 2008. Extended foot data-sheets and subsequently transcribed 4 South Australian Ornithologist 37 (1) into an electronic database.