The regent honey-eater.
Introduction and issues:
Some organisms are so rare, and at such low a number, that in a day’s time, and within the radius of a few kilometres, one can find a significant proportion of their existing population. One of these is the regent honeyeater (Anthochera phrygia, Shaw, 1794), which only has 350- 400 remaining individuals in the wild (Crates et al, 2017). This is a critically endangered bird, whose populations have declined by over 80% in the last three decades (BirdLife International, 2016). To observe this species in the wild, Aston, Shiyao, and I went to the Capertee Valley National Park, which is one of the last remnant habitats where they can be found breeding (Geering & French, 1998), and we met Ross Crates, who has been studying these birds since three years. Because of their nomadic lifestyle, these birds are usually difficult to monitor, but at Capertee, they have been nesting at the same spots since 3 years.
A google map of Capertee national park, with our site marked in white
A 3D google map image, of our site. It contains around 5% of the world’s regent honeyeater population!
A. phrygia is a nectivorous and insectivorous bird, endemic to NSW and S. QLD, that specialises on trees like the yellow box, iron bark, and mistletoe (Oliver, 2000). It has lost most of its habitat, because these trees exist on fertile land that was cleared for agriculture, or for timber, while remnant habitat exists in small isolated patches, which are heavily fragmented (Garnett et al, 2011). Today, most of their habitat is restricted to paddock trees. Our site, in the Capertee valley had a lot of these tree, hence becoming a stronghold for these birds. Ross said that the honeyeaters have faced an extinction vortex because of their small numbers. Before being at such low numbers, these birds would have flocked and travelled in groups, which would protect them from predation, but now, their vulnerability to predation is much higher. These birds also learn their calls from conspecifics, but because of their low numbers, Ross has been observing many of them make wrong calls, probably because they do not have enough conspecific individuals around them to learn the correct call (Liu et al, 2014), which is preventing them from finding each other, although, some have argued that this could be mimicry (Roderick, 2014; Veerman, 2016). They have also faced a sex ratio bias towards males, causing a skew in their mating system, with not enough females being around (Ewen et al, 2011). Their low numbers have also caused competitors, such as friarbirds, and noise miners, to outcompete them (Ford et al, 1993). I also hypothesize that they would be facing inbreeding depression, and future studies could look at this.
Flowers of the mistletoe: a favourite of the honeyeaters.
Ross’ research is trying to come up with solutions to conserve this species. One of the things he has done at Capertee, is the planting of over 300 trees of ironbark and yellow box. He says that even then, we would have to wait for a few decades, for the trees to be old enough to produce flowers and be suitable habitat. Till then, conservation efforts would have to prevent any further clearing of this habitat, and maintain the bird in low densities. Nectar is very important for the occurrence of this species, and he has found most of their habitat to be around nectar producing trees (Crates et al, 2017). Captive breeding programs and reintroduction have been undertaken for this bird, but even that has had its own problems (Liu et al, 2014), the main one being lack of suitable habitat where these birds can be released. So, even if we do increase their numbers, they wouldn’t breed, because there wouldn’t be enough nesting sites available. Ross is also using GIS to search for other suitable habitats where this bird may exist (Crates et al, 2017), or can be introduced into, which has been done previously (Oliver & Lollback, 2010). Till now, he has found a few hundred potential sites. He also studies site fidelity in this bird, and is testing whether they come back to the same site to breed, or migrate to different patches of land elsewhere. This would aid us to understand the movement of this species better, across a fragmented habitat, and measure the effects of habitat size and connectivity, on these birds. Fragmentation also creates edge effects, increases stochasticity, predation, and genetic problems, and it would be interesting to test whether such is the case for the honeyeater (Ford et al, 2001). We helped him monitor these birds, by looking for colour bands he had put on their legs, to see whether there were any new individuals in the area, or tagged individuals from previous years. We also searched for new individuals in locations he hadn’t surveyed before, and found 2 two new pairs that were about to start building their nests. This would allow him to create a spatial map of individuals, their nesting sites, and their feeding grounds. Ross is also trying to reduce predation on these birds and their eggs, by reducing their travel time between nest and water. He has placed water tubs near their nests, where they can go to for a drink. He also monitors their behaviour, and is testing whether nesting and breeding coincide with flowering of trees, and whether territoriality depends on the amount of flowers on a tree. He predicts that males would become more territorial, and spend more time chasing competitors away, when flowers come into bloom (Oliver, 1998). This could lead to lesser food being fed to chicks, which is a result of not enough nectar producing trees being around.
Old growth yellow box paddock trees in a fragmented agricultural landscape: a habitat for honeyeaters.
Ross says that most areas from where museum specimens for this bird were collected, are farms or urban areas now, and habitat is the biggest limiting factor for its recovery. He says that many honeyeater sites are still being converted to farms, and being offsetted inappropriately, to either unsuitable habitat, or areas which are too far away for migration, and offset restoration is being done by planting non-habitat trees. We noticed another limitation: water. Drought has been shown to reduce nesting success of these birds (Geering & French, 1998). During our visit, Capertee was completely dry, and had received much lower rain that previous years. Many saplings that Ross had planted had withered. Most of the individuals that we saw, were nested around mistletoes that parasitised casuarina, along stream banks. These sites are crucial for conservation of this species, because they have water even during drought years, and hence need to be prioritised for conservation, in order to save these birds. We helped Ross water the saplings, so that in 40 years’ time, they would grow into suitable paddock trees, and [hopefully] become nesting and feeding host spots for these birds. This also made me realise how water can be a limiting resource for an entire community of organisms. I wonder what impact climate change would have on such habitats, with increase in temperature and aridity, and greater unpredictability in rainfall.
Casuarina along streams, with mistletoes on them: suitable riparian habitat.
Aston watering yellow box saplings
The Park has also carried out culling of 400 noisy miners, which they think will increase the numbers of regent honeyeaters. Noisy miners are very territorial, and compete with honeyeaters for nectar, and often exclude them from suitable habitat (Clark & Grey, 2010). They also prevent lerp eating species, such as pardalotes and honeyeaters, from accessing iron bark and yellow box trees, which can cause a boom in lerp populations, leading to dieback of trees which are habitat and food for regent honeyeaters. Since the culling, Ross has observed regents in areas where they wouldn’t usually go to or nest in, due to competition from miners, and also an increase in honeyeater numbers. The honeyeaters also need the presence of birds, like the mistletoe bird, to facilitate their niche. The mistletoe bird propagates mistletoe seeds, from host to host, allowing mistletoes to parasitize their hosts, providing important food source for the honeyeater. We also helped Ross plant some new Mugger Iron bark saplings, which in the future, would restore their habitat. One problem with planting these trees is that they need low nutrient soil, but because the valley has been used for farming previously, it is rich in phosphorous, which causes exotic plants to outcompete natives (Lambers et al, 2013).
An area from where miners have been culled. New ironbark saplings were planted here.
Aston digs a pit, where new sapling will be planted. These will become habitat trees for honeyeaters, after a few decades.
We spent our last few hours sitting and looking at these rare birds, observing what they do, and appreciating this opportunity we got, to observe them before they may go extinct in the wild. I pondered on the joys of bird watching, something I hadn’t done since a long time. Our 3 day internship had come to an end. I not only learnt about the life history of, and conservation efforts for this species, but also got the privilege of being one of the few people in the world to observe this critically endangered bird in the wild. The regent honeyeater has a very small chance of surviving in the future, and it was surprising to see how much effort is put into saving a single species [without any guarantee], a species whose habitat we destroyed in an eye blink. There seems to be no effective short-term solution for this species’ conservation, because of its habitat being so limited, hence we need to conserve it long enough for our long-term habitat recovery plans to become effective. We also need a long-term monitoring program, that tests whether our efforts are meeting conservation objectives. I still remain optimistic for its survival, and hope that the little time we spent trying to restore its habitat and monitor it, is useful in its conservation.
A painting of honeyeaters, on the national park entrance. A flagship species that may soon be extinct.
BirdLife International. 2016. Anthochaera phrygia. The IUCN Red List of Threatened Species 2016: e.T22704415A93967301. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22704415A93967301.en. Downloaded on 07 September 2017.
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