Birds

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A total of 511 records of 47 species of birds were collected during wet and dry season surveys. Forty species were recorded in corridor planting sites and 29 species in the Lake Barrine reference site. Corridor sites shared 66-76% of the species recorded in Barrine. Bird diversity and the numbers of rainforest-dependent and mixed forest species were broadly similar between the forest reference and corridor plantings. Twenty-five rainforest-dependent species and five species confined to north Queensland’s Wet Tropics (endemics) were recorded in the corridor. This represents a threefold increase in rainforest species richness compared to Amy Jansen’s 2005 study (3), which recorded only eight rainforest-dependent species, none of which are endemic. 

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Importantly, Donaghy’s corridor is providing habitat for several IUCN red-listed Wet Tropics birds threatened by climate change. These include the endangered Wet Tropics brown gerygone and vulnerable Bower’s shrike-thrush and Victoria’s riflebird. However, some of the endemic and climate-sensitive species seen at Barrine remain absent from the corridor.

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Mammals 

During 2021/22, trail cameras were set out throughout the corridor every four months for five days. Mice (Mus musculus), grassland melomys (Melomys burtoni) and cane-field rats (Rattus sordidus), all rodents of grassland habitats, were captured in base-line surveys and were still present in 2000, but none were seen in 2021/22. Conversely, water rats (Hydromys chrysogaster) were seen throughout the corridor in 2021/22, but never in any previous surveys. Musky rat-kangaroo (Hypsiprymnodon moschatus) was recorded in the corridor for the first time; in 2000 the species was only trapped once - in reference forest.  All the forest-dwelling mammals recorded in 2000 remain present.

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Musky rat kangaroos and giant white-tail rats (Uromys caudimaculatus) are key dispersers of large fruits such as black walnut (Endiandra insignis) (weighing 125-240 grams) and yellow walnut (Beilschmiedia bancroftii) (weighing 30-90gms). Apart from cassowaries and gravity, these mammals are the only dispersers of these fruits, and the results of this dispersal are now evident. Seedlings of black walnut were recorded in four corridor survey plots, representing dispersal distances of 39, 64, 97 and 112m from the nearest potential mother tree. Seedlings of yellow walnut were also recorded in surveyed plots; a nearest mother tree is unknown but is at least >100m distant, representing minimum dispersal distances of 100, 127, 131 and 143m from the nearest potential seed source.

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Microbats

No microbat surveys were undertaken in 2000 (in fact, microbats had never been surveyed in restored rainforest in far north Queensland before this study). Over a 12 month period we set out bat call detectors throughout the corridor, in reference forest at either end of the corridor, and in the adjacent pastures.

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More than 95% of bat calls were reliably attributed to 12 species from six families – all are insectivores. Microbats in the corridor and reference forest were the same and comprised species of forest environments, e.g., the eastern horse-shoe bat (Rhinolophus megaphyllus) and the near threatened diadem leaf-nosed bat (Hipposideros diadema reginae). These bats are commonly known as ‘clutter-adapted’ species; broader wings allow them to forage in forested habitats where slower flight and the ability to manoeuvre in dense vegetation are required. Species detected in pasture sites differed markedly from those in corridor and reference forest, being dominated by narrower-winged, fast-flying species that forage in open areas, e.g., white-striped free-tail bat (Austronomus australis) and the northern free-tail bat (Chaerephon jobensis). Detectors also recorded the endangered bare-rump sheathtail bat (Saccolaimus saccolaimus nudicluniatus) – the first time this fast-flying species has been recorded in the tropical uplands (4). Without base-line data it is difficult to know how microbat colonisation has progressed. However, corridor vegetation is clearly the preferred habitat of microbats adapted to dense forest, and contains an abundance of their insect prey.

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Reptiles

Reptiles were studied by placing 24 log piles constructed of six old fence posts throughout the corridor and (after 6 months and 12 months) identifying the animals that took up residence. Five reptiles from two families (Scincidae, Agamidae) were recorded, in addition to two amphibians - the feral cane toad (Rhinella marina) and the vulnerable Australian lace-lid frog (Litoria dayi). Prickly forest skinks (Gnypetoscincus queenslandiae) and pale-lipped shade skinks (Saproscincus basiliscus) were the most common. The Australian lace-lid frog (1 site), and tiger skink (Concinnia tigrina) (2 sites) were the least common. Most log piles were also colonised by the venomous tiger centipede (Ethmostigmus rubripes rubripes).  

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Since planting, three species typical of intact forest - the prickly forest skink, tiger skink and Australian lace-lid frog - appear to have colonised the corridor. None of these species were captured between 1998 and 2000. Two pre-existing skinks, the pale-lipped shade skink and four-fingered shade skink (Saproscincus tetradactylus), have radiated throughout (5).

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Soil seed banks

Soil seed banks give an indication of how the restored forest might recover from disturbances including floods and cyclones. Seeds present in the soil (along with re-sprouting of existing trees) will determine the composition and speed of the area’s regeneration. Soil collection involved 24 samples, each 300mm x 300mm x 25mm, from the corridor and four equally sized samples from Lake Barrine reference forest, all at 20m from forest edge. Samples were germinated at the Lake Eacham Nursery and germinating seedlings were counted and identified at 30, 60 and 90 days.

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Corridor samples revealed 1673 seedlings of 41 species, comprising 26 natives and 15 weeds. Forest reference sites recorded 61 seedlings of 24 species, comprising 17 natives and 7 weeds. Twelve native species were common to corridor and reference sites; all the weeds found in forest samples were also found in the corridor samples. Red-leaf fig (Ficus congesta) was the most commonly recorded species, and Ficus was the most common genus, occurring in 23 of 24 corridor samples and 3 of 4 forest samples, with 273 individuals across seven fig species. Weeds recorded were all common and unlikely to affect the recovery of corridor vegetation, and results suggest corridor vegetation is capable of self-reorganisation after a major natural disturbance.

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So what do these studies tell us?

After 20 years, corridor vegetation has a similar habitat structure to mature rainforest – buttressed canopy trees, vines, orchids and ferns are all present, the first strangler figs have begun to appear on planted trees and many pioneers from the original planting are now large logs decomposing on the forest floor. But the vegetation composition remains distinctly different to mature forest which contains many more large trees comprised of a wider range of species.

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To rainforest wildlife, corridor habitat appears to be increasingly attractive. Musky-rat kangaroo, Victoria’s rifle bird, diadem leaf-nosed bat and the tiger skink are creatures of the rainforest; their growing presence indicates an increasing complexity of corridor habitat. Germination of large-fruited species sourced from outside the corridor is evidence of interactions with their specialised dispersers. Well-stocked soil seed banks suggest the restored forest is now potentially capable of withstanding natural disturbance.

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Lastly, this site is unique in terms of its size, age, the composition of the original plantings and its proximity to rainforest. Every restored area differs in these respects and these results reflect these factors. But what also makes this site unique is the knowledge gained. Few restoration projects collect base-line data and even fewer are monitored over time scales that allow meaningful insights into the processes of regeneration and colonisation.  

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References

(1) Tucker, N.I.J., Elliott, S., Holl, K.D., and Zahawi, R.A. (2023) Restoring Tropical Forests: Lessons Learned from Case Studies on Three Continents. In: Ecological Restoration: Moving forward using lessons learned (Eds) S. Florentine, L. Broadhurst, P. Gibson-Roy and K. Dixon. Springer-Link

(2) Tng, D.Y.P., Tucker, N.I.J, Apgaua, D.M.G.(2023) How does the forest structure, diversity and species composition of a restored rainforest 25 years after planting compare with that of mature rainforest? North Queensland Naturalist 53

(3) Jansen, A. (2005). Avian use of restoration plantings along a creek linking rainforest patches on the Atherton Tablelands, North Queensland. Restoration Ecology, 13:  275–283. DOI: 10.1111/j.1526-100X.2005. 00035.x

(4) Tucker, N.I.J and Ford, G. (2023) Observations on the utilisation of a restored wildlife corridor by echo-locating microbats in North Queensland’s Wet Tropics. Ecological Management and Restoration DOI: 10.1111/emr.12576

(5) Tucker, N.I.J., Colman, D., and Snodgrass, P. (2024) Using log piles to assess reptile habitat development in Donaghy’s Corridor. North Queensland Naturalist 54