Egg oiling with liquid paraffin BP is approved for use under the Control of Pesticides Regulations (COPR) but can only be used under licence provided by the Department of Environment, Food and Rural Affairs (DEFRA) under Section 16 (1) of the Wildlife and Countryside Act 1981.
It is an offence to interfere with a nest or its contents and therefore, before taking any action to remove a nest with or without eggs or chicks, or to oil eggs within a nest, permission must be sought from the Department of the Environment, Food and Rural Affairs (DEFRA).
Egg oiling is considered to be an extremely effective method of non-lethal and humane bird control but is not commonly used for the control of urban species such as the feral pigeon. Egg oiling is a method of egg treatment that is normally used for the control of ground nesting birds and is considered to be 100% effective if carried out at the correct time of year. The only exception to this rule would be where egg oiling is used for the control of roof-nesting birds such as the gull. Although the gull does not nest at ground level the process has been successfully adapted to be used as part of a gull control programme where birds are nesting in accessible areas at height.
Egg oiling involves the use of liquid paraffin BP to coat the shell of the egg in order to stop the embryo from developing. Liquid paraffin BP is a white mineral oil, commonly known as paraffin oil. When an egg is removed from the nest and fully immersed in liquid paraffin BP the oil blocks the pores of the egg, coating the underlying egg membrane and depriving the fertilised egg of oxygen. In order for the process to be completely effective the whole of the egg must be coated leaving no gaps or ‘dry’ areas. DEFRA recommends the use of a wide-necked container or small bucket for dipping the eggs. Once immersed in the liquid paraffin BP the egg must be turned 360° several times to ensure that the whole egg is coated. DEFRA recommends that the operator should wear protective gloves and a facemask to comply with Control of Pesticides Regulations (COPR) but confirms that a gloved hand will not remove liquid paraffin BP from a coated egg. Liquid sprays or sponges should not be used to coat the egg as these methods of coating may leave some areas of the shell untreated.
Once the egg has been dipped in liquid paraffin BP it should be allowed to drain before being replaced in the nest. The nests and eggs that have been treated should be marked to ensure that they are not revisited and re-oiled more often than is necessary. The major benefit of this method of egg treatment is that the parent will be unaware that the egg has been interfered with and will continue to incubate the eggs for the requisite period. Other methods of egg interference include the following:
- Breaking eggs (in the nest)
- Pricking eggs (using a pin or needle to make a hole in the shell of the egg that will allow bacteria to enter the egg as well as desiccating the contents)
- Removing eggs
- Cracking eggs
- Shaking eggs
- Removal of eggs and the provision of dummy eggs
All of these methods of egg interference are not only illegal, unless a licence has been obtained from DEFRA, but they are also ineffective, with the possible exception of removing eggs and replacing them with dummy eggs. When eggs are interfered with by any means other than egg oiling with liquid paraffin BP, the parent will normally re-lay another clutch of eggs immediately, rendering the process of interference pointless. Dummy eggs are likely to be accepted by the parent but only if the dummy egg is an exact replica of the real egg, not only in size and colour but also in weight. When using egg oiling it is important to be aware that if the target species commonly lays more than one clutch of eggs per season it is possible that re-laying will occur once the parent has incubated the treated eggs for the normal period (ie. for pigeon control this period would be 19 days).
As each and every species of bird lays a particular number of eggs (within a range), and as each species will spend varying periods laying and incubating their eggs, the timing of each egg oiling operation is critical. Some species of birds lay 12-15 eggs, some only 2 or 3. Some species breed all-year round others only produce one clutch per year. It is therefore also critically important to have in-depth knowledge of the target species before applying for a licence to oil eggs and before undertaking any oiling operations. As egg oiling operations can be highly labour-intensive, particularly where the control of waterfowl is concerned, a well-planned and structured species specific program must be provided. Failure to do so will compromise the success of the operation.
Where the control of species such as the feral pigeon is concerned egg oiling can be an extremely effective method of control when combined with a loft-based control system. A system of this nature would normally involve the use of an artificial breeding facility such as pigeon loft where pigeons are encouraged to roost and breed as an alternative to their normal roosting and breeding sites. As pigeons breed all-year round any control system involving the use of egg oiling would need to be provided throughout the year with particular attention paid to the period March-October, this being the height of the breeding period. Although human interaction would be required throughout the whole year the act of oiling and marking eggs and nests in a loft-based environment would only take minutes per week.
Egg oiling is most commonly associated with the control of Canada goose populations due to the fact that Canada geese are becoming a growing problem in the UK with static populations of non-migratory birds increasing every year. As with the control of most species of bird, effective Canada goose control systems involve the use of several control techniques with egg oiling being considered to be one of the most effective options. Egg oiling regimes must be well planned and require nesting sites to be monitored prior to nests being built and clutches being laid. Clutches must be oiled immediately after the final egg has been laid on sites where multiple nests exist and for single breeding pairs the eggs should be oiled 3 days after the last egg has been laid. Canada geese start to lay in the second half of March with most eggs being laid in the first half of April. It would therefore be necessary to visit the breeding site 3 times; at the end of March, mid-April and the end of April. All eggs should be oiled throughout this period and by doing so it is highly unlikely that the parent will re-lay once past the end of the normal incubation period.
For the control of large gulls in urban environments egg oiling can be an extremely effective method of control, particularly when used as the main control option alongside the installation of deterrents and anti-perching devices. Gulls are normally colonial, sometimes breeding in mixed colonies and laying their eggs between mid-April and late June. Gulls will either breed on flat-roof areas, normally in numbers, or solitarily on or beside chimney pots or other difficult-to-access areas at height. Nests will need to be visited several times during the course of the breeding period to ensure that all the eggs are oiled. Clutches should be oiled as soon as incubation has started. As with Canada geese, constant monitoring will be required but as gulls tend to habituate to the same nesting site each year the monitoring process may be more straightforward. Although the installation of deterrents and anti-perching devices may be required, egg oiling, if carried out consistently and thoroughly, will be 100% successful as a birth control option. It may also have the effect of moving the birds on to other breeding sites permanently due to their lack of success in rearing young on the site concerned. This process is likely to take 2 to 3 seasons before the birds permanently desert the site.
Egg oiling is a cheap, humane and 100% effective method of control that can be used in a variety of situations and for the control of a wide variety of bird species. When used for the control of some species, such as wildfowl in rural areas, the act of oiling may be labour intensive, thereby increasing the cost of the operation. However, the fact that this method can be 100% effective relative to conventional controls such as shooting, which are completely ineffective (and in some cases act to increase population size as a result of rejuvenation), egg oiling has to be considered to be one of the most effective methods of control available.