This sisal by-product is for the birds

Nesting logs to improve biodiversity.

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About 40 years ago, government-funded projects saw thousands of hectares of marginal land in South Africa planted to sisal plantations. Agava sisalana, a native to Central America, would create much- needed employment in the former homelands and produce a valuable low-cost multi-use plant fibre.

Time and cheap synthetic alternatives caught up with our fledgling sisal industry and the plantations fell into disuse, eventually being abandoned. In many places, sisal spread and became a nuisance invader, reducing the value of vast tracts of land. It also left behind something initially regarded as worthless – the tall flower stalks.

Resembling an aloe in structure and appearance, a sisal plant produces leaves in a rosette pattern from its ground level base. This takes place over seven to 10 years, then the plant sends up a tall central stalk with flowers on the tip. Once it has flowered and set seed, it dies and dries out along with the rest of the plant.

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A nest log excavated and used by a pair of crested barbets. Note the toothpick, used as an activity indicator.

Cavity nesters
Ornithologists and bird watchers soon saw a use for these stalks as material for nesting logs for cavity-nesting birds such as barbets and woodpeckers. In the last 25 years, this has led to a small informal home industry with several players and as-yet unfathomed potential for increasing biodiversity in especially urban areas.

The principle is simple. Cut off the top of the stalk at a convenient length – 1,2m – above the dried leaf and root base. Trim off the dried leaves and roots. Seal the cut top of the stalk with a coat or two of thick paint to prevent water absorption. Drill an appropriate-diameter pilot hole 50mm deep at a right angle into the side of the stalk about 150mm below the top and affix the log firmly to the underside of a slightly sloping tree branch. The pilot hole will soon attract bird cavity resting species which, if undisturbed, will excavate a cavity in the soft wood for nesting or roosting.

Principles of the nesting log
Any primary or secondary cavity- nesting species in your area may occupy the nest. Primary cavity-nesting species excavate their own cavities; secondary cavity-nesting species use abandoned pre-excavated or natural cavities; The pilot hole attracts primary cavity-nesting birds. Its diameter determines which species will use the log – 40mm is a good size for barbets and woodpeckers; The pilot hole must face south or east; There should be no foliage within 1,5m of the hole; Don’t disturb the bird while it is excavating its cavity.

Nest logs are available from EcoSolutions at R100 (R140 installed). – Chris Nel

Phone EcoSolutions on 011 791 7326.

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