In 2006 we conducted a trial on two moors in the Angus Glens to test the effectiveness of using acaricidal leg bands attached to hen red grouse in reducing the impact of sheep ticks on the survival of their chicks.
The leg bands, containing 8.5% alpha-cypermethrin, reduced tick burdens on chicks and increased their survival relative to broods from untreated hens. Treated hens were distinguished from untreated (control) hens by different coloured wing tags. However, low re-sighting rates of marked birds prevented us from detecting a significant difference between experimental groups. Consequently we conducted a second trial in the spring of 2008 on the same moors, but this time using radio-tagged hen grouse to ensure sufficient re-sightings.
We caught 40 red grouse hens at night in March and fitted them with radio collars. We tagged 10 hens at each of two sites on one moor and 20 hens on the other. At each site, we randomly selected half the hens and fitted them with acaricidal leg bands containing 8.5% cypermethrin, a synthetic pyrethroid, and fitted the remaining hens with placebo leg bands as controls.
We tracked the hens weekly until they laid clutches and began incubating. We disturbed the hens from their nests once, usually in mid-incubation, to count and measure the eggs. Neither clutch size, which averaged 9.0 eggs, nor hatch date, with a median date of 24 May, differed between experimental groups of hens. Before breeding, the transmitters or their signals were lost from four of the 40 hens, one was killed by a mammal and one probably died from disease. A further four hens were killed by raptors while foraging away from the nest during incubation and a final hen died immediately post-hatch for no apparent reason. All of the remaining 29 hens successfully hatched their clutches.
We caught chicks from each of the 29 broods when they were 10 to 12 days old and counted the number of ticks attached to their heads. The average tick burdens on chicks differed between the three study sites. On Moor A, only one tick on a treated chick was found at site 1 and two ticks, both on untreated chicks at site 2. However, Moor B proved very ticky and significantly more ticks were found on the chicks of untreated hens than on those from acaricide-treated hens (see Table 1).
|Moor||Site||Acaricide-treated chicks||Untreated chicks|
|Sample size||Ticks/chick||Sample size||Ticks/chick|
At approximately seven weeks old, we relocated and flushed the broods to get a final count of the chicks. Across all sites, there was a tendency for higher chick survival from treated hens. However, this trend was not significant, with 36% of chicks from treated hens surviving and 20% of untreated chicks surviving at seven weeks old. However, when data from site 1, which had virtually no ticks, were excluded, survival of chicks from treated hens was 49% (+9 se) compared with only 18% (+8 se) from control hens (see Figure 1).
These data collected this year tend to confirm earlier findings in 2006; that is, equipping hen grouse with acaricidal leg bands helps to reduce tick burdens on their chicks and that this in turn results in higher chick survival. However, these findings are interim and we need to repeat it again in 2009. Given that two of our study sites had so few ticks, next year we will revise our site selection to ensure that all sites have tick problems. We cannot yet recommend the use of acaricide leg bands as a management tool to enhance grouse productivity in ticky areas.
|Figure 1. Chick survival from hen red grouse on sites 2 and 3 combined|
|Treated hens = 10; untreated hens = 11|