These methods are designed to prevent the eggs from hatching, thus stabilising or reducing the size of the colony.
It is essential to check the appropriate Natural England General License each year to ensure that these techniques are still permitted.
The incubation period of Lesser Blackbacked and Herring Gulls is approximately 25-26 days. If the nests and eggs are destroyed every 3 weeks this will prevent any eggs from hatching. The Gulls will probably nest again and re-lay so the process will need to be repeated throughout the nesting season (May to August). This should result in a year on year reduction in bird levels.
Oiling the eggs (dipping them in light paraffin oil) seals the shell and effectively sterilizes it. The birds, however, are duped into thinking it is still viable and will continue to sit. At this time they are actually very quiet, disturbance is therefore significantly reduced. As no chicks hatch the particularly noisy aspect of the breeding cycle is removed. The eggs must be oiled as near the laying time as possible this will depend with the season but will normally be around the first week of May. After about 4-6 weeks the eggs will start to deteriorate and they will be ejected from the nest. Mature birds will lay a second or even third clutch, and if the technique is to be successful these will need oiling as well.
As well as cutting down on noise, oiling may slowly disperse the colony. Although more research is needed it is thought that unsuccessful females will find a new mate and therefore nest elsewhere (this could of course be the adjacent roof).
Dummy eggs have also been shown to be successful. Plastic eggs are available which look like gulls eggs. These are then substituted for the real thing. This method has the same advantages as egg oiling but there is the added benefit that less frequent visits to the nest are needed.