Tracking change in the Wet Tropics: what long-term bowerbird monitoring is revealing
- Dominic Chaplin
- Feb 26
- 4 min read
Updated: Mar 2
Dominic Chaplin | Bowerbird Monitoring Project Leader
Detecting ecological change in complex rainforest systems requires patience, consistency, and long time-frames.
In the Wet Tropics of Far North Queensland, BirdLife Northern Queensland has been undertaking exactly this kind of work through long-term monitoring of bowerbirds and other rainforest specialists – species that are difficult to survey, but potentially sensitive indicators of environmental change.
Since the early 2000s, volunteers led by Bowerbird Monitoring Project Leader, Dominic Chaplin, have revisited fixed survey sites across a broad altitudinal range, recording bowerbird activity and conducting repeat rainforest bird counts along standardised transects. The strength of this Project lies not in any single survey result, but in continuity: the same locations assessed repeatedly over decades, using stable and well-documented methods.
Golden Bowerbird
Persistence despite predicted vulnerability
Climate-change theory predicts that high-altitude specialists may be among the first species affected by warming temperatures, as suitable habitat contracts upslope. The Golden Bowerbird (Prionodura newtoniana), which occurs predominantly above 1,000 metres, has therefore long been considered a species at potential risk.
However, long-term bower monitoring tells a more nuanced story. More than 100 Golden Bowerbird bowers have been located since surveys began around 2008, with known sites in some cases monitored for nearly 50 years.
In 2025, the majority of accessible bowers remained active, with only a small number abandoned due to localised vegetation damage. Importantly, all historical bower locations recorded prior to 2000 continue to be occupied, with a handful of exceptions linked to cyclones, habitat fragmentation, or site-specific disturbance rather than a systematic movement from their current altitude.
At present, there is no evidence of broad-scale range contraction or upslope movement in Golden Bowerbirds. While this does not rule out future impacts, it suggests a degree of resilience within currently available habitat, and highlights the value of long-term site-based monitoring in testing widely held assumptions about climate vulnerability.
Tooth-billed Bowerbird
A concerning signal from a Key Indicator Species
In contrast, results for the Tooth-billed Bowerbird (Scenopoeetes dentirostris) warrant closer scrutiny. This species is particularly well suited to long-term monitoring: males construct their courts at largely fixed locations for decades, and during the breeding season (approximately September to December), they call loudly and frequently from near these sites. At any given time, around 70% of birds are vocal, making repeatable counts feasible under consistent conditions.
BirdLife Northern Queensland’s monitoring program involves walking approximately 30 selected one-kilometre rainforest transects at least once every two years, recording the number of Tooth-billed Bowerbirds heard calling, along with other bird species. Between 2021 and 2025, 181 kilometres of transects were surveyed using this method.
The resulting data show substantial year-to-year and site-to-site variability, which is expected in rainforest bird surveys and makes short-term interpretation difficult. However, when considered alongside earlier research by James Cook University – which identified the Tooth-billed Bowerbird as showing the greatest decline of any Wet Tropics bird species over a 17-year period – recent results raise concern. While the signal is not yet statistically definitive, there are indications of declining detections at some sites over the past five years.
Given the species’ suitability as an indicator and its known sensitivity to environmental change, continued monitoring over the next decade will be critical to determine whether these patterns reflect genuine population decline, or natural variability. The emerging trend reinforces the importance of sustained observation rather than reliance on short-term studies.
Broader rainforest bird trends
Abundance versus threat status
Beyond bowerbirds, surveys also record a suite of other Wet Tropics species, including 13 birds reclassified as Threatened in 2020. One recurring challenge highlighted by the data is the apparent mismatch between perceived abundance and conservation status.
Several species listed as Vulnerable or Near Threatened – such as Grey-headed Robin, White-throated Treecreeper, and Eastern Whipbird – are recorded frequently and may appear locally common.
Conversely, some species that are rarely detected remain unlisted. This apparent contradiction reflects how threat assessments are made: not on local detectability, but on total area of occupancy, habitat specialisation, and long-term range trends.
A species can be locally abundant while still declining overall if its viable habitat is shrinking. In the context of climate change, an emerging hypothesis is that some birds are being compressed into narrower altitudinal bands as lower-elevation habitat becomes unsuitable. Under this scenario, numbers at mid- or high-altitude sites may temporarily appear stable, or even increase, masking early population declines until available habitat near mountain summits becomes limiting.
Interpreting rainforest bird data with care
Rainforest bird monitoring is inherently challenging. Many species are cryptic, vocalise intermittently, or mimic others. Detectability varies with observer experience, weather, time of day, and season. For some taxa – particularly scrubwrens, thornbills and fernwrens – under-recording is likely, and results beyond presence or absence must be interpreted cautiously.
Rather than weakening the Project, this transparency strengthens its scientific value. The aim of the program is not to generate precise population estimates, but to detect directional change over time using consistent methods applied across decades.
Why long-term monitoring matters
Taken together, the findings underline the importance of sustained ecological monitoring in the Wet Tropics. In systems where change is gradual and signals are subtle, short studies can be misleading. Only long-term, repeatable observation can distinguish true trends from background variability.
BirdLife Northern Queensland’s bowerbird surveys are building that evidence base – not by claiming certainty, but by documenting change carefully, acknowledging limitations, and ensuring that when shifts become unmistakable, they are recognised early enough to inform conservation action.
Visit the Birds With Altitude page for more information.
All photos © Dominic Chaplin
