Effects of fly disturbance on the behaviour of a population of reintroduced Przewalski horses ( Equus ferus przewalskii) in Mongolia

Abstract

Flies constitute a cost to animals by feeding from them, passing on disease or by preventing them feeding effectively. These costs could be more severe to animals suffering from some kind of stress such as reintroduction as part of a conservation programme. This study focused on the effects of fly disturbance on Przewalski horses ( Equus ferus przewalskii) reintroduced into Hustai National Park in Mongolia. As the reintroduced horses could not be handled, we took three approaches: direct fly sampling, sampling flies on a ridden domestic horse ( Equus ferus caballus) and monitoring their behaviour, and observations of Przewalski horse behaviour. Flies were sampled in traps and on a domestic horse in grazing and resting places used by the Przewalski horses; more flies were found in valley grazing places than ridge resting places. The number of flies was related to temperature, with most found between 15 °C and 30 °C, peaking at 22 °C, however taken together no environmental or seasonal variable satisfactorily explained the number of flies. Comfort behaviour, the behavioural response of horses to the presence of flies, increased with temperature and decreased with wind speed in both domestic and Przewalski horses, and increased with elevation for Przewalski horses. During warm months Przewalski horses had a daily pattern of moving up to high, bare places where there was no forage during the warmer hours of the day. It is likely that they moved to escape flies, but were followed by them. The cost of flies to horses and their potential impact on the reintroduced population is discussed.