Oakley Dam Walk

KRM Branch 21st August 2022

KRMB branch’s field outing for August was to Oakley Dam at Marrinup on the Darling Scarp above Alcoa’s Pinjarra Alumina Refinery. The dam was established to provide water for steam trains but is no longer used for that purpose. Surrounded by Jarrah Forest, the dam is situated in an area with numerous outcrops of granite. A total of 15 members and visitors turned out on a fine morning to attend this walk on which Heather Adamson guided us.

At the carpark and along the track down to the dam, we soon found Winter Donkey Orchids (Diuris brumalis) and Blue Beard (or Fairy) Orchids (Pheladenia deformis) with a couple of Dark-banded Greenhoods (Pterostylis sanguinea) with extremely crowded flower stalks harder to spot in amongst a dense shrub. In this area, we later spotted a Little Pink Fairy Orchid (Caladenia reptans subsp. reptans). The Granite Petrophile (Petrophile biloba) was flowering along the track, as were three species of Hibbertia, small Drosera sp., plus the Purple Mirbelia (Mirbelia floribunda).

As we came to the dam, we were treated to a chorus of frog calls. A recording submitted to the FrogID app identified that there were three species of frogs calling, the Rattling Froglet (Crinia glauerti), Ticking Frog (Geocrinia leai) and Slender Tree Frog (Litoria adelaidensis).

At the dam itself, we could see that it was full to overflowing following good winter rainfall. Here, we heard a different frog call, the distinctive quack call of the Red-thighed Froglet (Crinia georgiana), a species that prefers moist situations such as under granite rocks and logs. A recording taken by Heather Adamson was submitted to the FrogID app, and the experts confirmed our identification.

There were no water birds on the dam, but woodland birds were sighted, including Carnaby’s Black Cockatoos, Red-tailed Black Cockatoos, White-cheeked Honeyeater, New Holland Honeyeater and Brown Honeyeater. A Fan-tailed Cuckoo was heard calling but proved elusive to spot. Splendid Fairy Wrens, Inland Thornbills, White-browed Scrubwren, Dusky Woodswallows and Black-faced Cuckoo-shrikes were also spotted. A Purple-crowned Lorikeet was a nice sighting, as was a Wedge-tailed Eagle (our only raptor sighting). A Laughing Kookaburra made our total 14 species for the morning, though we could not identify some little canopy birds due to their fleeting sightings.

Near the small bridge across the stream that flows into the dam, there were fungi on small dead trees, including a Yellow Brain Fungus (Tremella mesenterica group) and an unidentified fan-shaped gilled fungus.

Image by Colin Prickett

On top of the large granite outcrop that overlooks the car park and picnic area, we found the Resurrection Plant (Borya scirpoidea) in flower, plus Yellow Candles (Tripterococcus brunonis) and a tiny Boronia sp. Gullies in the granite were filled with Blind Grass (Stypandra glauca), causing Heather to make a mental note to return during spring to see the plants in flower.

After a final cuppa at the picnic area, it was time to leave. It had been a great morning at a very scenic (and popular; lots of other visitors were present) site. On the way out, a few of us stopped at the intersection of North Spur Road and Scarp Road, where a small fire had occurred. Here we found Swan River Myrtle (Hypocalymma robustum), Jug Orchids (Pterostylis recurva) and Calothamnus quadrifidus in flower, along with an impressive display of Bracket Fungi on the burned trees.

Colin Prickett