The free-roaming horses that inhabit the Shackleford Banks of North Carolina appear to take advantage of local wind patterns to reduce their harassment by biting flies, researchers report.
The Shackleford Banks is a barrier island system on the coast of Carteret County, which is home to a well-known herd of wild horses.
Daniel Rubenstein and Lisa Feinstein, writing in the journal Frontiers in Ecology and Evolution, observed the Shackleford horses for a two-month period during late spring and early summer to learn more about their fly avoidance strategies.
The pair said horses in the United States are harassed by many species of biting flies.
Apart from being a nuisance, their bites can lead to blood loss and transmit disease. Horses, therefore, tend to avoid areas where fly numbers are high.
Environmental factors such as low wind speeds and high temperatures can also increase fly problems for horses. Similarly, coat color matters because darker horses attract more flies than lighter ones, especially on hot, sunny days.
The pair said many horse populations reduce fly loads by living in large groups or by bunching tightly together.
“Shackleford horses do so, too,” they said. However, they also use wind speed differences among habitats to keep the fly problem in check.
“By adopting a systematic pattern of moving between habitats such that they only visit a habitat when wind speed is high enough to keep fly harassment to a tolerable level, they can avoid being bitten while continuing to forage,” Rubenstein and Feinstein reported.
Typically, they begin the day foraging on the salt marshes where fly abundance is inherently low and is lowered further by faint early morning breezes.
Later in the morning, the horses move to grassy swales when increasing wind speeds reduce fly landings there to levels found on the marshes.
Later still, when wind speeds peak, the horses begin foraging among the sand dunes.
“At this point wind speeds are high enough so that horses using any habitat will be minimally harassed by flies, thus enabling them to freely choose where to feed based on which habitat meets particular dietary needs for protein, energy and nutrients on any particular day.
“Hence, Shackleford horses follow the breeze to solve a challenging dilemma of maintaining a high nutritional plane without succumbing to fly harassment.”
The researchers said other free-ranging horse populations appear to have more limited options, thus limiting their decision-making options.
Rubenstein DI and Feinstein LH (2021) Bothersome Flies: How Free-Ranging Horses Reduce Harm While Maintaining Nutrition. Front. Ecol. Evol. 9:659570. doi: 10.3389/fevo.2021.659570