Border Ranges 2020

Conserving grassy habitat for the Eastern Bristlebird

In 2013 I was privileged to join a committed group of landholders, researchers, National Parks staff and conservationists working to save the northern population of the Eastern Bristlebird. Once fairly widespread in the grassy forests each side of the NSW / Queensland border, population numbers of this ‘little Aussie battler’ have declined sharply since the 1980s.

Unlike Bristlebirds further south, our birds favour tall eucalypt forests with a thick understorey of native tussock grasses. These grassy forests are also home to other small, rare native species, including the Hastings River Mouse.

An Eastern Bristlebird, and its grassy habitat 10 months after a low-intensity ecological burn. Key native grass species include Wild Sorghum (Sorghum leiocladum), Snow Grass (Poa sieberiana), and Kangaroo grass (Themeda triandra).

Our study area is in the Border Ranges, along the Lyons Road between Kyogle in NSW and Beaudesert in Queensland. Local monitoring had already identified the central role of fire in maintaining habitat values.

In this highly productive environment where the volcanic soils are fertile and rainfall is usually high, grassy forests form a mosaic with rainforest. Without the frequent low-intensity fires once lit by graziers – and the Githabul people before them – grasses decline and woody plants increase, shading out grasses. Since the 1980s, this process has happened rapidly, degrading large areas of what was once prime Bristlebird habitat. Many once-grassy forests have now completely ‘shrubbed up’, their Bristlebirds long gone.

Here's the Bristlebird story, told from a Queensland perspective.

Border Ranges landscapes. This country is mountainous, wet and fertile. Clouds often shroud the hills, adding moisture via 'cloud drip'. In the photo above you can see darker rainforest and grey-green eucalypt forest side by side.

Our job was to determine how fire affected the invading woody species, with a view to figuring out what fire regimes would keep them at bay, maintain existing grasses, and assist degraded patches to recover. Over a period of years we tagged almost 1000 plants, going back after and between burns to record whether they had survived - and how many new woody plants had appeared. Our most recent site assessment was in January 2020.

Over this time the Bristlebird Recovery Team has had various other projects on the go, including a captive breeding program to get additional birds ready for release. Wild birds have been checked regularly, sometimes with the aid of a detector dog. Around 2014, PhD student Zoe Stone joined the team, taking Bristlebird research to a new level. Aerial photos from 1966 have been compared with remote sensed images from 2009, to see how habitat quality and extent have changed. Burns have been carried out, both in national park and on private property. Massive effort has gone into weed removal.

What did we find?

Much of this research is still on-going, with several papers in draft. Here’s my understanding of where we're up to (June 2020).

Zoe Stone’s research confirmed that places where Bristlebirds are still found have a thick grassy understorey. The larger the grassy patch, the more likely it will support Bristlebirds.

Zoe’s research also linked Bristlebird presence directly to frequent fire, confirming previous findings from long-term monitoring.

Comparative mapping showed that grassy habitat in the Border Ranges had declined by almost 50% between 1966 and 2009.

Early findings from our tagging study documented the resilience of woody plants to a single fire, particularly after a long interfire interval (‘long’ is maybe 10+ years in this productive environment). Seven months after fire there was a slight decline in woody plants where the most recent interval between fires had been 5 years, but a massive increase where the last inter-fire interval was 14 years. Seedling wattles accounted for much, but not all, of this increase. Rainforest species also increased their stem numbers, mostly by coppicing from roots.

In January 2020 we recorded considerably reduced numbers of woody plants after two 5-year inter-fire intervals. However this was also after years of drought. The whole place was looking pretty shabby, in both burnt and unburnt areas, with many native grass tussocks looking like they might not recover. Let’s hope we continue to get good rain, and grasses revive.

The good news is that bird numbers in the wild are up a little. And the captive breeding program is going well.

Bristlebird habitat 2.5 years after an ecological burn.

Here’s Zoe Stone’s journal article about Bristlebird habitat. You can access Zoe's full thesis here.

Here’s a presentation on the mapping work (NCC Bushfire Conference, Sydney 2017). The slides with maps are hard to follow, but there are also slides showing habitat, methods and conclusions.

Here's a presentation about the initial results from our tagging study (Bushfire 2016 Conference, Brisbane). Click the PDF symbol.

And here’s a pictorial record of regeneration after the ecological burn in the photo above.