This is another way of doing it by making a simple plastic insert out of a piece of 50mm OD uPVC pipe that stays in the wall. It is a lot easier to make these inserts than making formers.
As an experiment, I bought 2 metres of grey pipe from Homebase for £3.99 (see here). This pipe has an internal diameter of 46.5mm, which both Starlings and Swifts can get into. If such a pipe is squashed then it should exclude Starlings but still admit Swifts.
The pipe is cut into 40mm pieces, placed in an oven at 120°C for 10 minutes, then pressed into a D-shape using a flat piece of wood with another piece attached to it to control the height.
With a flat piece of wood 44mm wide by 29mm high, the width of the entrance piece is 57mm
With 30mm wide by 31mm high, the width is 56mm.
Starlings should not be able to enter either of these entrances, but the 31mm high one may be easier for Swifts.
Finally to give the Swifts some grip, the floor is scored with a soldering iron to make a toe-hold.
Disclaimer - this idea has not yet been tried on a project, but it is so simple and cheap that anyone could do it. Further work is needed to establish the optimum height that will exclude Starlings.
|A piece of 50mm pipe, an entrance being shaped and a finished entrance with scoring.|