Researchers at the Animal and Plant Health Authority (APHA) has been working of an oral contraceptive that will hopefully offer a way to reduce grey squirrel populations in a humane and effective manner.  The contraceptive targets a mammalian hormone known as GnRH [Gonadotropic Releasing Hormone].  This hormone stimulates squirrels to ovulate or produce testosterone.  The contraceptive stimulates the production of antibodies against the GnRH so that the animals are rendered sterile.  However, there are problems with the contraceptive.

• It affects other species, such voles, wood mice, and dormice if they feed in the ‘traps’.
• Ensuring its effective means of delivery to grey squirrels alone.

To address these issues, APHA has be experimenting with different designs of baited ‘traps / feeders’ to deliver the contraceptive so that only grey squirrels can enter.  The bait for these ‘traps / feeders’ is hazelnut butter mixed with rhodamine B.  The rhodamine B is added as it causes the fur of grey animals that have taken the bait to fluoresce under UV light, it may also colour the fur of the squirrel to PINK. Red squirrels cannot reach the bait as they are not heavy enough to trigger the internal mechanism of the trap / feeder.  A recent test of the mechanism revealed 19,000 visits by grey squirrels but only 9 by mice, so it does effectively distinguish between different woodland species.  There is now a plan to test the traps / feeders on a much larger scale in Cumbria, Northumberland, South Scotland and Lancashire.  Perhaps technology may be used to follow the behaviour of the animals at the 'traps' - e.g. trail cameras / infra red photography.

Modelling by APHA of the contraceptive and modified traps suggests that grey populations might drop by half within six years.  Other methods to reduce the grey squirrel numbers include:

• The introduction of Pine Martens in suitable areas, which predate more successfully on grey squirrels, as the red ones are somewhat nimbler.
• Incentives for landowners to create more woodland.  

Further information : https://aphascience.blog.gov.uk/2018/10/09/red-squirrel/