Eye-orbital swellings in Dippers on the Welsh Borders

Abstract

On 5 December 2019 Stephanie Tyler (SJT) and Rachel Shepherd (RES) were mist-netting on the Afon Honddu in the Llanthony Valley of the Black Mountains in Monmouthshire and caught four Dippers Cinclus cinclus gularis coming in to roost at a bridge at the Neuadd, Cwmyoy. One adult male had a puffy ring around the eyes and marked swellings above both eyes. On 29 November 2020, at the same bridge, SJT and RES retrapped an adult female with a slight swelling. SJT then looked through some photos of Dippers taken by Mick Jenner at one of her nest sites at Maesyberan on the Afon Honddu on 2 June 2017 and noticed that one of a side view of a Dipper which she had labelled ‘dipper with eye injury’, had a similarly enlarged orbital ring. SJT contacted Tony Cross (AVC), a keen Dipper ringer, to see if he had caught similarly affected birds. It transpired that AVC had first noticed eye problems in Dippers on 30 January 2005, when he had taken a photo of an affected bird. He put out the photo online, in a post on the old Ringers’ Forum, asking if any ringer had seen a similar problem, but had had no response. Since then, he has caught Dippers with swollen eye orbits on several occasions, including: on 7 April 2019 on the Rhydhir Brook, Rhayader; on 6 January 2020 on the River Clun, near Clun, and at Beambridge, Aston-on-Clun; on 9 January 2020 at Afon Peiran, Cwmystwyth; on 4 January 2021 on the River Onny, Plowden; and on 5 January 2021 on the Quinney Brook, Grove Park, Craven Arms, at Middleton near Ludlow and on the River Onny at Stokesay. The main feature of the waterways where Dippers with swollen eye orbits had been noted is that, in late 2019 and early 2020 and again during the winter of 2020/21, they had all been in continuous spate for up to three months with no respite, and the water turbidity was exceptional, with a suspension of bright reddish-brown sediment from the land. The increased water depth and turbidity were not usual for these waterways, in the experience of the authors who have observed them for over 40 years, although seems to be becoming more common as spate conditions become more frequent. Williams (1997) noted that many disease processes can affect the avian eye and periorbita; periorbital swelling can be an indication of a primary ocular disorder or may occur secondarily to sinusitis. Sinusitis is fairly common in birds that are human companion animals, such as parrots and cockatoos, leading to periorbital swellings (Stiles & Greenacre 2001, Graham et al 2003). In January 2020, AVC and SJT contacted Gareth Thomas (GT), a retired vet from Ludlow with an interest in Dippers, sending photos, and he in turn contacted Dr Neil Homer-Forbes who is a dedicated avian vet with an interest in exotics and wildlife. At first, they considered whether a specific waterborne disease, with a possible parasitic or mycoplasmal aetiology, might be responsible for the symptoms shown in the photographs. GT, in discussion with another avian specialist vet from the English Midlands, Jason Waine, then suggested that it could be a type of traumatic ‘boxers’ eye’, resulting from the birds’ habit of continually forcing their way into stony riverbeds when searching for food, often with little or no underwater visibility and driven by hunger because of a prolonged spell of difficult feeding due to floods. GT noted that in very forceful currents some water may enter the bird’s nasal cavity, finding its way into the sinuses, which are much more extensive than in mammals. Any such ‘brown’ water will be carrying some contamination, even if only sterile soil particles, which will likely cause some mild sinusitis. If GT’s hypothesis was correct, the eyes would be expected to improve gradually as a river spate eases and the water becomes clearer; as the fluid in the swellings should disperse when feeding activity becomes less traumatic.