Respiratory cryptosporidiosis in red grouse

Infection is more prevalent in young red grouse. © Laurie Campbell

BACKGROUND Infection by Cryptosporidium baileyi, a parasitic protozoan, causes respiratory cryptosporidiosis in red grouse. It was first diagnosed in 2010 and has spread with infection rates higher in young birds. Understanding underlying causes of disease emergence and routes of infection transmission are fundamental to its subsequent control. Respiratory cryptosporidiosis was first diagnosed in red grouse on a North Pennines moor in the autumn of 2010. In the next three years, respiratory infection by the protozoan parasite Cryptosporidium baileyi, which is confined to birds but includes several orders, had manifested itself in red grouse on half the moors in northern England and 80% of moors in the North Pennine Hills. C. baileyi is typically associated with high densities of birds, either released gamebirds or captive collections of birds in aviaries and zoos. Initially, we hypothesised that outbreaks in red grouse were also density related following the recent increases in both breeding and pre-shooting stocks across many moors in the English uplands.

In this account of the impact of respiratory cryptosporidiosis on grouse population dynamics, we fitted 111 diseased and 67 healthy grouse with radio-transmitters at two North Pennine moors where disease prevalence averaged 8.1% and monitored their survival and productivity between autumn 2013 and autumn 2015. Six-month natural survival rates (excluding birds that were shot) were 70% in healthy grouse, but only 44% in diseased females and 22% in diseased males. Some 39% of diseased birds died from their infection, whereas 28% of healthy birds were shot. A similar proportion of each group were killed by predators, either by stoats or raptors. On average, diseased

females bred eight days later than their healthy counterparts, but neither clutch size, egg volume or nesting success differed in relation to disease status. Productivity was 43% lower among pairs with a diseased member than in healthy pairs, but appeared impaired only if the female was diseased, not the male. Differences in productivity were related to chick survival rather than the proportion of pairs that reared broods, with chick survival being lower in the 10 days after hatching and again when chicks were 20-50 days old. This latter period was when respiratory infection among chicks was first noticed and the on-set of infection may have been a contributing factor to higher mortality during this period. Described levels of respiratory infection reduced the number of birds available to shoot in August by 6%, which represented a mean annual loss of £0.9 million in revenue across managed grouse moors. Likely reductions in shoot economics could escalate should prevalence increase.

We have continued monitoring disease prevalence involving screening in excess of 45,000 grouse shot at 10 North Pennine moors over the period 2013-18. Analysis of these data has shown that prevalence is twice as high in juveniles as in adults, it fluctuates across years in relation to annual breeding success and is highest in the years immediately following the first observations of disease on a given moor. There is no evidence for an escalation of prevalence over time, but we will continue limited annual monitoring at a smaller subset of moors in future years. Respiratory cryptosporidiosis has to-date largely been confined to the Pennines, especially the more northerly dales, and verified reports have been absent from the North York Moors, Trough of Bowland and all Scottish moors. These absences are despite similar densities of grouse to those in the Pennines on several moors in these UK regions, suggesting that outbreaks and subsequent prevalence may not be directly density-dependent.

This disease is a welfare concern and potentially a conservation concern too should infection cross to other bird species occupying the same moors. A screening programme of black grouse occupying the fringes of moors where red grouse are infected has been conducted over the last three years. Despite in-hand examination of birds caught at night for research purposes, together with close-quarter visual examination of displaying males at leks and testing of droppings, we have found no sound evidence of respiratory cryptosporidiosis occurring in this species.

KEY FINDINGS Respiratory cryptosporidiosis was first diagnosed in red grouse as recently as 2010 and within three years was observed on half of driven grouse moors in northern England, most of those in the

North Pennines. Infected female grouse bred a week later, produced only half the fledglings and survived only half as well as their healthy counterparts on the same moor. Impacts of disease on shooting have to date been slight due to low prevalence in the population, which currently shows no sign of increasing. Despite a programme of screening, the disease has not been found in black grouse.

David Baines

David Newborn Mike Richardson

Philip Warren

The disease has not been found in black grouse. © Dave Kjaer

ACKNOWLEDGEMENTS We acknowledge the generous funding provided by Roger Henderson QC on behalf of the G & K Boyes Charitable Trust.