How to make a house martin nest
To make your own nest cup for house martins you will need some exterior gap-filler or a mixture of cement and sawdust, and a mould to make the nest the right shape. A child's plastic ball measuring about 18 cm across is ideal. If you have to buy one, choose a cheap, smooth and shiny one without a bladder. One ball will make four moulds.
For each nest cup, you will also need a piece of rough, un planed wood about 30cm by 20cm.
Step by step
· To make the mould, divide the ball into equal quarters with a marker pen, and cut carefully along the lines with a sharp knife (Figure 1).
· Mark and cut out the entrance hole to the nest cup. This needs to be a semi-circle 60mm wide and 25mm deep. Stick pieces of masking tape to the inside of the mould, leaving plenty of overlap (Figure 2).
· Drill three screw holes in the piece of wood for fixing. If you want to remove the nest easily from the eaves, cup hooks can be fitted in place of screws at this stage.
· Place the mould on the wood flush with the top edge and stick down the loose ends of the masking tape to attach it. Pack the mould with newspaper to make it firm (Figure 3).
· Pour a thick layer of filler over the exterior of the mould so it overlaps thickly onto the wood. Smooth the mixture with a knife into an even layer about 1 cm thick (Figure 3).
· Leave the covered mould at room temperature until it is completely set inside and out. Then carefully remove the ball mould, paper and masking tape (Figure 4).
· Seal the joint between the inside of the cup and the wood with a worm of wood glue. Allow to dry thoroughly. Plaster the outside of the cup with wet mud and allow to dry before hanging the nest cup (Figure 5).
· Fix the nest cup under the eaves so it sits flush in the corner. The overhang of the eaves needs to extend far enough to provide the nest protection from the elements. If you have several nest cups, fix them in groups for best results.
· There is some indication that house martins prefer to nest on east or north-facing walls, but walls in any direction are used.