Australian Field Ornithology 2019, 36, 124–129 http://dx.doi.org/10.20938/afo36124129 The importance of Hutt Lagoon and fossil river estuaries to shorebirds in mid Western Australia M.J.C. Singor¹*, Linda Giblett² and C. Heap3 ¹149a Bishopsgate Street, Carlisle WA 6101, Australia ²Unit 39, 140 Teranca Road, Greenfields WA 6210, Australia 3P.O. Box 216, Byford WA 6122, Australia *Corresponding author. Email: [email protected] Abstract. Little is known about the dynamics of the shorebird populations of the mid Western Australian coastline between Kalbarri and Geraldton, as this area is remote and sparsely populated. We surveyed shorebirds at several sites in this region, including fossil river estuaries from intermittent rivers (Hutt, Bowes and Greenough Rivers) and wetlands on the western shoreline of Hutt Lagoon and around Port Gregory. Totals of 21 migratory shorebird species and 9 Australian-breeding shorebird species were recorded from 64 visits in 2006–2010 and 87 visits in 2017–2018. The highest counts related to Banded Stilt Cladorhynchus leucocephalus (652), Red-capped Plover Charadrius ruficapillus (300) and Red-necked Stint Calidris ruficollis (300). The highest numbers of most species were recorded at Hutt Lagoon and associated semi-permanent wetlands near Port Gregory, with mean counts in 2017–2018 of 109 migratory shorebirds (mainly Red-necked Stints) and 227 Australian-breeding shorebirds (mainly Banded Stilts), from the accessible part of that wetland system. This shows the importance of such wetlands in providing shorebird habitat in the region. None of the wetlands met criteria for international importance. Introduction There is a large stretch of the Western Australian coastline, from Geraldton (425 km north of Perth) to Kalbarri (167 km north of Geraldton), for which little information on shorebirds is available. This coastal area between Kalbarri (592 km north of Perth) and Geraldton is generally dry and barren and largely devoid of suitable sites for shorebirds. Available sites are limited to some small fossil river estuaries and Hutt Lagoon (a large coastal salt lake with associated smaller wetlands). The coast itself consists of Figure 1. Port Gregory and Hutt River. Google Earth narrow sandy beaches backed by dunes or cliffs, and the beaches are generally too steep and exposed to ocean waves to provide important habitat for shorebirds (though this was not checked during the current study). Fossil estuaries are formed by inland rivers that flow to the coast only during winter or periods of heavy rainfall. They empty into the ocean for short periods and in some years not at all. The river mouth is closed by a sandbar and a small pool of water often remains during the year, attracting shorebirds, although in some years this will dry out over summer. This paper presents results of surveys of those sites in this 167-km stretch of Indian Ocean coast, in an endeavour to fill some of the gaps and provide baseline data for future studies. The shorebird surveys were conducted over two distinct periods (2006–2010 and 2017–2018). Figure 2. Port Gregory town drainage ponds. Photo: Linda Giblett Study area sites was conducted in 2017–2018 and was extended to In 2006–2010, the study area was the wetlands along the include the Bowes River estuary (28°24′S, 114°27′E) and causeway leading to Port Gregory (28°11′S, 114°15′E) Greenough River estuary (28°51′S, 114°38′E). (Figure 1), on the western side of Hutt Lagoon. It included the town drainage ponds in Port Gregory (Figure 2), small Hutt Lagoon (Figures 4–5) is a large shallow salt lake wetlands around the township and the Hutt River estuary near the Indian Ocean coast, just north of the mouth of the (28°13′S, 114°18′E) (Figure 3). A repeat study of these Hutt River, in the mid-western region of Western Australia. Shorebirds at Hutt Lagoon and fossil river estuaries, Western Australia 125 Figure 3. Hutt River estuary. Note the sandbars partially Figure 4. Hutt Lagoon wetlands, causeway and lake. Note blocking the mouth of the fossil river estuary. Photo: the large flock of shorebirds, mainly Banded Stilts and Linda Giblett some Red-necked Avocets. Photo: Linda Giblett Figure 5. Hutt Lagoon from Port Gregory causeway. Photo: Figure 6. Bowes River estuary. Photo: Linda Giblett Linda Giblett Figure 7. Greenough River, at low water level. Photo: Linda Figure 8. Greenough River estuary, at high water level. Giblett Photo: Linda Giblett It is ~14 km long, ~2.3 km wide, and runs parallel with the ~7 km south of Port Gregory and is generally closed by a coast. In this study, it is taken to cover the wetlands on both sandbar. The Hutt River estuary (Figure 3) contains pools sides of the causeway leading into Port Gregory as well as of water even over summer, possibly derived from springs, the samphire Halosarcia sp. shoreline extending from the and the water is generally brackish (Brearley 2005). causeway out to the spit in a north-westerly direction. A small lake south of the causeway was created when the Bowes River is situated south of the township of road closed off part of the inlet. Water pipes run through Horrocks. When in flood, this small river flows into the Indian this lake to supply seawater to the evaporation ponds in Ocean. A large estuary lagoon forms behind the sandbar Hutt Lagoon. When in operation, seawater leaks out of (Figure 6), and there are pockets of samphire along the the pipes and into the lake, thereby maintaining a viable riverbanks and a small floodplain on the southern side of shorebird habitat over summer. The Hutt River is located the river mouth. 126 Australian Field Ornithology M.J.C. Singor et al. The Greenough River estuary (Figures 7–8), the 2017: a nest with four eggs (4 September), another clutch largest estuary surveyed, enters the Indian Ocean at (21 October) that failed, and an adult with three juveniles Cape Burney just south of Geraldton, and extends for a (21 October). Black-winged Stilts used a large exposed considerable distance inland. Its mouth is usually closed mudflat, ~1 km upstream on the northern side, of the by a sandbar and accumulations of seagrass. Composition Bowes River estuary to roost and feed. of beachwrack is variable, depending on the material available in the offshore environment but here generally Discussion contains the genera Amphibolis, Posidonia and Halophila (Wells 2002). The wetlands around the Port Gregory causeway (Hutt Lagoon) and the drainage ponds in Port Gregory were the Methods sites most valuable to shorebirds as they contained water throughout summer. These sites combined had the highest Shorebird surveys were conducted over two distinct number and diversity of species. Hutt Lagoon is a very periods. The first surveys were conducted mainly during shallow ephemeral salt lake that dries out over summer, February and March in 2006–2010 and covered the and any variation in the volume of water entering it will wetlands at Hutt Lagoon, shorebird sites around the Port impact on shorebird habitat. This was evident when the Gregory township and the Hutt River estuary (Heap 2008, remnants of tropical cyclone Joyce caused heavy rainfall 2009). Surveys from June 2017 to June 2018 covered at Port Gregory over the weekend 13–14 January 2018: these same sites and, in addition, the Bowes River and Hutt Lagoon filled quickly and flooded the samphire fringe, Greenough River estuaries. All sites were covered on foot. and triggered heightened shorebird feeding activity along Estuaries were surveyed by walking along the riverbanks the edge of the lagoon. Large sections of Hutt Lagoon have on both sides, including the sandbars. Access to the tracks never been surveyed and this site potentially supports a along each river depended on water levels. Surveys were much larger shorebird population. conducted from one to five times a month. Two types of brine shrimps live in Hutt Lagoon and feed on the microscopic green alga Dunaliella salina. The native Results brine shrimps Parartemia, which prefer less-saline water, are often abundant in pools around the fringing marshes Numbers of shorebirds counted are summarised in after rain. The other type of brine shrimp Artemia, an Table 1 (maximum and mean counts of each species introduced species, is more salt tolerant (Brearley 2005). at each site; all scientific names are listed in Table 1) Brine shrimps are a known food source for Banded Stilts and Table 2 (monthly counts at four of these sites in (Marchant & Higgins 1993; Pedler 2017). 2017–2018). More shorebirds were counted at Hutt It is evident that Hutt Lagoon is a minor coastal refuge Lagoon than at other sites, with maximum counts of ~1600 for the Banded Stilt. The maximum number of this species (sum of maxima for all species for years 2017–2018 at Hutt recorded there in this study was 652, though their numbers Lagoon) compared with <300 at any of the three fossil river might have been higher as large sections of the lagoon estuaries. Up to 1121 Australian-breeding shorebirds and were not surveyed. Numbers of Banded Stilts fluctuated 466 transcontinental migratory shorebirds were counted from year to year, with counts >100 in 2006, 2007, 2010, at Hutt Lagoon, compared with 158 and 125, respectively, 2017 and 2018. The juveniles sighted at Hutt Lagoon In at the Greenough River estuary and fewer elsewhere September 2017 had probably originated from the breeding (Table 1). Transcontinental migratory shorebirds formed event of January 2017 in the western desert from the ~25% of the overall mean counts of shorebirds. The most Eastern Pilbara across the border to the Northern Territory. numerous Australian-breeding species were Banded Stilt, Red-capped Plover, Black-winged Stilt and Red-necked The smaller fossil river estuaries (Hutt and Bowes Rivers) supported low numbers of migratory shorebirds.