"Bulgy eye" in red grouse

A new problem currently facing grouse stocks is the disease colloquially known as “bulgy eye”. 

Until recently, outbreaks of “bulgy eye” (caused by the bacteria Mycoplasma gallisepticum) had been confined to pheasants and partridges, and the appearance of the same symptoms amongst red grouse were blamed on infected birds moving up from the low ground and spreading the disease amongst grouse.

Recent research has revealed that the symptoms described as “bulgy eye” in grouse are actually caused by a totally different species of bacteria – Cryptosporidium baileyi. There is currently no explanation for why or how this disease has suddenly appeared amongst wild red grouse populations.

Birds infected with C. baileyi exhibit very similar symptoms to those suffering from M. galliseptum, which effectively mimics severe sinusitis. The tissue around the eyes becomes extremely swollen with a cheesy pus, leaving the grouse blind. In extreme cases, death results after starvation or predation, and there is evidence to suggest that the disease could become a serious issue for the future of grouse management.

It is known that infections are caused when grouse inhale or eat C. baileyi bacterium, and early research suggests that infection “hot-spots” could well be around grit stations, particularly where there are splashes or puddles. The best advice currently on offer is to increase the number of grit stations so that birds are not concentrated around just a few and to spread sand or wood chips around the immediate vicinity of grit boxes in order to keep the ground dry. There are treatments available for C. baileyi, but these are so toxic that they are impractical for use on wild birds.

It may also be relevant to consider biosecurity measures for the moor, since it has been suggested that humans and dogs could be responsible for transmitting the disease.

Anyone who finds a grouse which they believe is suffering from “bulgy eye” should contact the GWCT or St David’s Game Bird Services.