The Capertee River flows west to east, joining the Wolgan River at their confluence in Newnes. The river is fed by a number of minor tributaries in the upper reaches and forms part of the Hawkesbury-Nepean catchment. From the upper reaches of Bogee River to Glen Davis, the Capertee river flows through the Capertee Valley, which is internationally recognised and designated as an important bird area (IBA) by BirdLife International. This designation is principally due to the fact that the Capertee Valley is the core breeding range of the critically endangered Regent honeyeater. Once distributed throughout south eastern Australia from south Queensland to Adelaide, the species has suffered a major and ongoing population decline and associated range contraction. Current population estimates suggest there may be only 300-400 birds remaining. The Capertee Valley is now recognised as the core of the species’ breeding range, and is the only site in Australia where the species can be seen on a semi-regular basis.
The Regent honeyeater is a ‘rich patch specialist.’ This means that for successful breeding to occur, individuals must locate rich sources of nectar with which to provision young, in habitat that provides dense cover to conceal nests from predators. The most important breeding site for regent honeyeaters in the Capertee Valley is the banks of the river itself. This riparian habitat of river she-oak Casuarina cunninghamii provides the nesting substrate required by regent honeyeaters. The stretch of the river in the vicinity of Genowlan bridge holds breeding birds in most years, (including the present year), as does the open valley floor of the Capertee National Park. The riparian habitat is also of vital importance because the river she-oaks play host to a species of needle-leaf mistletoe, Amyema cambagei. The flowers of the needle leaf mistletoe are another important nectar source for breeding regent honeyeaters. The river itself provides their only source of drinking and bathing water. During hot weather, birds can be seen frequently taking water from the river, and bathing to help regulate body temperature. A regular supply of water is likely to become increasingly important for breeding Regent honeyeaters given projected climate change scenarios. In addition, the river provides a bountiful supply of invertebrate fauna, which is an important source of protein for both adult and young birds. It is highly likely that the abundance of insects in the vicinity of the river is determined by the presence of water in the river. Also critical to the successful breeding of the regent honeyeater in the valley is the flowering of a small number of key eucalyptus species, in particular Yellow box E.melliodora, White box E.albens and Mugga ironbark E.sideroxylon. It is widely appreciated that the frequency and intensity of flowering in these species is moderated by soil moisture content; periods of low soil moisture are associated with poor flowering events, which in turn moderates the frequency of breeding opportunities of the Regent honeyeater.
Given the importance of the riparian habitat of the Capertee valley described, any drop in the water levels in the Capertee River is highly likely to have a significant detrimental impact upon the long-term persistence of the Regent honeyeater in the wild. A reduction in water levels is likely to reduce both the frequency and intensity of flowering in nearby eucalyptus species, as well as in the long-term persistence of both the river she-oak and needle-leaf mistletoe. Lack of access to water during the breeding season may either result directly in mortality of offspring during hot weather or indirectly by increasing the risk of nest predation if parents are forced to commute further from the nest to obtain water. Alternatively, it may also inhibit the initiation of breeding altogether. A reduction in invertebrate fauna in foraging areas of breeding regent honeyeaters would also limit the protein resources to provision chicks, which could either cause offspring mortality of have negative effects on the long-term health of the birds. In summary, a regular and plentiful supply of water in the Capertee river is fundamental to the functioning of the entire ecosystem, of which the regent honeyeater plays a critical part.