Home Technical Feature Major Mitchell’s Hollows Artificial Formation Of Tree Cavities – Part 3

Major Mitchell’s Hollows Artificial Formation Of Tree Cavities – Part 3

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A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis): for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri).

Restore

The deterioration of cavities can reduce their quality to a point where they are no longer suitable for nesting by cockatoos long before they are lost to tree fall or fire (Hurley, 2009; and Saunders et al., 2014). Collapse of the nest chamber roof and walls due to decay and weathering exposes the nest chamber to rain, reducing the insulating quality of the cavity and exposing eggs and nestlings to the risk of drowning from flooding (Hurley, 2006a). The accumulation of wood debris and decayed material can result in cavities becoming too shallow to provide suitable shelter or protection from predators (Saunders et al., 2014).

We used a method similar to that of Saunders, et al. (2014) and Hurley (2009) to restore collapsed cavity floors by placing rounds of timber into the cavity, followed by a layer of coarse chip and finally a layer of fine clean Callitris woodchips ofa texture mimicking that produced by the MMC. Missing cavity roofs or walls were replaced using a Callitris section carved to fit the cavity spout and sealed into place with wedges of timber and silicone sealantand tech screwed.

Another strategy is to replace a collapsed cavity floor by screwing in place a sub floor of wire mesh. On top of this build up a stable cavity floor of Callitris chips to the desired depth (Figure 22).

Cracks in the nest chamber wall were also filled with wooden wedges and silicone sealant; or for larger sections, replaced by affixing sections of timber carved to provide a firm fit (Figure 25)

It is imperative that these sections are well fitted to prevent gaps and are glued and secured in place with long wood screws or coach bolts where necessary.

The collapse of nest chamber floors caused by the progression of heart wooddecay can also result in nest chambers Figure 32 becoming too small or exposing jagged wooden spikes of un-decayed wood (Figure 27 and Figure 28), both of which have been found to prohibit nesting of large cockatoo species. Saundersetal. (2014) did report successful breeding by Carnaby’s Black-Cockatoo, in WA, after restoring cavities by in-filling collapsed nest chamber floors. We further developed this technique for application in Callitris in Pine Plains (Figure 29 and Figure 31).

Nest-box

The creation of and installation of nest-boxes is a last resort action for the conservation of cavity dependent fauna. It is an admission that all other conservation and management action shave failed. Installing nest-boxes creates a Figure 34 requirement for ongoing maintenance and active management of these structures. In conservation reserves where wildfires have removed large numbers of cavity bearing trees it may be necessary to replace some with nest boxes.

Nest-boxes were made from salvaged windfall Callitris logs.

For a safe work environment, a tension tie-down strap was used to secure the log in position when using power tools on each log. A biscuit was sliced from the top and base of each log using a chainsaw to provide a clean surface (Figure 32). Immediately after each cut was made the newly exposed end grain was painted with a log sealer to prevent the ends of the log from splitting (Figure 33). For this we used Mobil Log Seal©. Without an end-grain sealant, once cut, the timber tended to split very quickly (Figure 34). A second thick coating of log seal should be applied. As a further precaution strapping is placed around the top and bottom of each log to further reduce splitting (Figure 35).

Once the ends of the log have been secured the main cuts in the log can be made to create and remove the face plate (Figure 36 and Figure 37). This is best done by first cutting two cross cuts ~ 70 cm apart and not more than 1/4 the circumference of the tree at the height of the cuts. Then make two longitudinal cuts with the chainsaw bar held at a 45° angle for each on either side of the tree starting one at a time from just below one end of the top cut and continuing down to the lower cut (Figure 36). Repeat this on the other side. The angling and depth of the longitudinal cuts should allow the cuts to meet in the middle of the trunk at a right angle all the way along the cuts. The faceplate should naturally fall lose once the final cut is complete (Figure 37).

The wedged shape provides a more robust strThe inside face of the faceplate must be carved so it has internal concave contours to match the curvature and wall thickness of the cavity being carved from the inside of the tree trunk (Figure 44 and Figure 45). The cavity entrance can also be carved from the faceplate (Figure 46) or may be carved out of the nest-box on the oppositeucture to the nest-box by leaving more of the nest-box intact as a single piece (Figure 38). Put the face plate to one side while working on the nest-box proper. To efficiently clear the large amount of material required to form the nest cavity, use a chainsaw to create longitudinal cuts along the internal length of the log (Figure 39). This creates internal slabs that can be further split with a pinch bar and lifted out (Figure 40).

The main cavity, can be worked with two Arbortech blades on separate angle grinders. Once the internal slabs have been removed to create a cavity use the Arbortech© to sculpt the interior walls and floor and deepen the cavity if necessary (Figure 41 and 42).

The inside face of the faceplate must be carved so it has internal concave contours to match the curvature and wall thickness of the cavity being carved from the in

side of the tree trunk (Figure 44 and Figure 45). The cavity entrance can also be carved from the faceplate (Figure 46) or may be carved out of the nest-box on the oppositeside to the face-plate (Figure 47 to Figure 49). These carving tasks are best done with an Arbortech© blade attached to an angle grinder.

Once the interior of the nest-box is nearing completion, the entrance can be made in the log on the side opposite to the faceplate (Figure 47 and Figure 49). It is recommended to carve the entrance to nest-boxes on the opposite side to the face-plate so the face-plate can be placed against a tree trunk and provide further protection from damage by large parrots (Figure 49) (Hurley, 2009).

Use the Arbortech© blade attached to an angle grinder to clean and smooth-off any rough edges to the cavity entrance from both within and outside the nest-box (Figure 50 and 51). Final adjustments can be made to the interior of the nest-box such as carving climbing holds for the birds and ensuring the caulking timbers cover all gaps between the walls and the faceplate. Ply wood fill in the gap created by the kerf width of the chainsaw blade (Figure 52). It is recommended to use timber slats and then glue and screw the face-plate securely in place.

References

Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Johnson, R.D., Kleinig, D.A., McDonald, M.W. & Turner, J.D. (2006) Forest Trees of Australia. CSIRO Publishing, Collingwood.

Bond, J. (2006) Foundations of Tree RiskAnalysis: Use of the t/R ration to Evaluate Trunk Failure Potential. International Society of Arboriculture – Arborist News:

Carey, A.B. & Gill, J.D. (1983) Direct habitat improvement – some recent advances. In: Snag habitat management symposium, pp. 80-87. Forest Service General Technical Report Curtis, A., Green, J. & Warnock, B. (2000) Mimicking natural breaks in trees. English Nature, 8:1, 19-21.

DSE (2011) Guideline 8.1.42: Working in the vicinity of hazardous trees. Vitorian Government Department of Sustainability and Environment, East Melbourne.

Fay, N. (2002) Environmental arboriculture, tree ecology and veteran tree management. The Arboricultural Journal, 26:2, 129-136. Forbes-Laird, J. (2008) THREATS: Tree Hazard: Evaluation and Treatment System. Forbes-Laird Arboricultural Consultancy, United Kingdom. FWPRDC (2004) The In-ground Natural Durability of Australian Timbers. Forest & Wood Products Research & Development Corporation, Australian Government, Canberra.

Gibbons, P. & Lindenmayer, B.D. (2002) Tree hollows and wildlife conservation in Australia, 1st edn. CSIRO Publishing, Collingwood. Gibson, M., Florentine, S. & Hurley, V.G. (2008) Age distribution of Slender Cypress-pine (Callitris gracilis) within Pine Plains, Wyperfeld National Park. Centre for Environmental Management, University of Ballarat, D.O.S.A. Environment, Ballarat.

Hurley, V.G. (2006a) Physical characteristics and thermal properties of Major Mitchell’s Cockatoo, Cacatua leadbeateri leadbeaterinest hollows, Wyperfeld NP. Department of Sustainability and Environment, Mildura. Hurley, V.G. (2006b) Survey of Major Mitchell’s Cockatoo in Pine Plains, Wyperfeld NP – Spring 2006. Department of Sustainability and Environment, Mildura.

Hurley, V.G. (2009) A report on installing nest boxes and repair of degraded nest hollows in Callitris Pine for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri) in Pine Plains, Wyperfeld National Park. Unpublished report prepared by the Department of Sustainability and Environment for the Mallee Catchment Management Authority, Mildura. Hurley, V.G. (2011) Results from the 2010 breeding survey of Major Mitchell’s Cockatoo (Lophocroa l. leadbeateri) Pine Plains, Wyperfeld NP. Department of Sustainability and Environment, Mildura.

Hurley, V.G. & Harris, G.J. (2014) Simulatingnatural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). Department of Environment and Primary Industries, Mildura.

Kenyon, P. & Kenyon, P. (2010) Pruning for habitat workshop.

Korpimäki, E. & Higgins, P.J. (1985) Clutch size and breeding success in relation to nest-box size in Tengmalm’s Owl Aegolius funereus. Holarctic Ecology, 8:1, 175-180.

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management. HMSO, 1999.

Mattheck, C. & Breloer, H. (1997) The Body Language of Trees. HMSO, London.

Rowley, I. & Chapman, G. (1991) The breeding biology, food, social organisation, demography and conservation of the Major Mitchell or Pink Cockatoo, Cacatua leadbeateri, on the margin of the Western Australian wheatbelt. Australian Journal of Zoology, 39:2, 211-261.

Saunders, D.A., Mawson, P.R. & Dawson, R. (2014) Use of tree hollows by Carnaby’s Cockatoo and the fate of large hollow-bearing trees at Coomallo Creek, Western Australia 1969–2013. Biological Conservation, 177:1, 185-193.

SWA (2011) Draft Code of Practice: Safe Access in Tree Trimming and Arboriculture. Safe Work Australia, Canberra.

Taylor, A.M., Gartner, B.L. & Morrell, J.L. (2002) Heartwood formation and natural durability a review. Wood and Fiber Science, 34:4, 587-611.

VTIO (2010) Draft Climbing Guidelines Victorian Tree Industry Organisaion, Ringwood.

Figure 47: Initial cut into back of nest-box to form entrance.

Figure 48: Marks on inside of nest-box indicating dimension of entrance.

Figure 49: Cavity entrance opened and ready for finishing off rough edges.

Figure 50: Arbortech being used to hollow out and form the cavity entrance.

Figure 51: Arbotech being used to smooth-off and from external entrance features.

Figure 52: Plywood caulking planks tacked and glued into place. Wood glue placed on interior gluing surface ready for attachment of face plate.

Figure 52: Plywood caulking planks tacked and glued into place. Wood glue placed on interior gluing surface ready for attachment of face plate.

Figure 54: This nest box has a metal plate, top and bottom to further protect timber from rotting and splitting. The nest box is resting on the stump of a cut branch.

Figure 55: Note the face plate is facing into towards the tree trunk.

Hurley, V.G. & Harris, G.J., (2015) A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). A report to the Department of Environment, Land Water and Planning, Melbourne.

For more information please send an email to Grant Harris at http://grant@ ironbarkenviroarb.com

Visit the website www.ironbarkenviroarb.com

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