I read that tree tubes can be a hazard for young birds. They get in them for insects etc but then find they cannot get out. Some tubes have been found with many dead birds. I am not sure whether this problem is recognised in this country but in America tree tubes have to have a 'top' to prevent entry by birds.
With the many thousands of tree tubes in Calderdale, standing for years on end, does anyone know if there is a problem with dead birds locally?