Streaked Shearwaters near Rottnest Island

Streaked Shearwaters are relatively common visitors to waters off northern Australia, but there are few (if any) records from the seas off Perth, and certainly no recent records. Hence it was something of a surprise when the recent pelagic trip organised out of Hillarys Boat Harbour recorded good numbers just north of Rottnest Island. The first birds were recorded c. 12km NNE of Rottnest Island (c. 15km off the mainland) on the outward passage of the boat. Several birds were seen in this area, but no further birds were seen on the outbound journey. However, on the return journey, several more Streaked Shearwaters were recorded c. 8km NW of Rottnest, and larger numbers (probably 20+) 2-5km due N of Rottnest Island. Overall, it was estimated that 40+ birds were recorded on the trip.

A Streaked Shearwater with the Perth skyline in the background, April 2012.



Location of Streaked Shearwater records on April 2012 pelagic. Click here for full Google Map.



The presence of such a (relatively) large number of Streaked Shearwaters raises some interesting questions. The species is known to occur regularly in waters as far south as the Abrolhos Islands [1], but there are few reliable records south of this area. Mathews is cited as stating that it’s distribution included “seas off south-western Australia” [2], but there do not appear to be any details about any records on which this may be based. More recently, there are several seawatched records from the Dunsborough area [3], though these should be treated with caution given other improbable reports from the area. Is it possible that they are in fact a regular visitor to Perth waters at this time of year that have been overlooked in the past? There have been few pelagic trips organised off Perth at this time of year – in fact this trip was the first for over 15 years. However, the birds were not seen well offshore, and would’ve been easily visible from Rottnest Island – it seems difficult to believe that they’ve been completely overlooked in these numbers previously!

Streaked Shearwater off Perth, with Rottnest Island in the background, showing proximity to the island.



There are other possible explanations. Our namesake, the Leeuwin Current, has been particularly strong this year, largely attributable to the La Nina episode experienced across late 2011 and early 2012 [4]. This had led to particularly warm water temperatures off Perth (24oC and higher). Streaked Shearwaters are a predominantly tropical species that prefer warmer waters, so it may be that the particularly high water temperatures this year drew them further south than usual.

Several Streaked Shearwaters off Perth, April 2012.



Another possible factor in this record is the recent passage of Tropical Cyclone Lua through inland WA. This resulted in several seabird records from well inland, including a live Streaked Shearwater at a minesite near Leonora [5] and another picked up dead near Menzies [6]. It may be that the influx of Streaked Shearwaters was related to this weather event.

It is hoped that we will be able to organise another trip this time next year to see whether the shearwaters are present again, and shed more light on this record. The location of the sightings (close to Rottnest) means that some land-based seawatching from Rottnest in autumn may also be valuable.

References
[1] Johnstone & Storr (1998). Handbook of Western Australian Birds Volume 1: Non-passerines. WA Museum.
[2] Lindsey (1986). The Seabirds of Australia. National Photographic Index of Australian Wildlife. Angus & Robertson.
[3] Observations. Western Australian Bird Notes 079 & 080.
[4] http://www.sciencewa.net.au/topics/fisheries-a-water/item/1286-little-penguins-famished-by-strong-leeuwin-current 
[5] http://birdswa.org.au/sightings.htm
[6] WA Museum, pers. comm.