Abstract:
Ticks and their pathogens cause significant disease
and economic loss in many animal populations. Despite
this, experiments that test the impact of ticks and tickborne
diseases on wild animal populations are rare. Here,
we report on an experiment assessing the effect of ticks
on red grouse productivity and chick growth in relation to
other causes of poor recruitment at two sites in the
Scottish uplands during 2005. Treated hens received two
leg bands impregnated with the acaricide permethrin,
while controls hens were untreated. Chicks were captured
at c.2 weeks of age and fitted with a metal patagial tag,
and chicks from treated hens also received a permethrinimpregnated
strip. Mean tick burdens in treated chicks
were close to zero compared with a mean of around 12
in the control group. Although treatment reduced tick
infestations, it did not increase brood size. Growth rates in
chicks from control and treated hens were similar during the first 10 days and comparable with chicks fed an ad-lib
invertebrate-based diet. These results suggest that in this case,
neither ticks (and the tick transmitted louping-ill virus) nor
food shortages was the main cause of chick mortality.
However, mortality in the adult hens was around 35 %, and
predation accounted for 62 % of these losses before broods
fledged. Our results indicate that on our study sites, predation
may have a more important impact on grouse population
dynamics than ticks and tick-borne disease. We suggest that
it may be more cost effective to determine the causes of poor
grouse population performance before implementing popular
but expensive tick control measures such as the culling
of alternative hosts and running acaracide treated sheep
‘tick-mop’ flocks.
