付記する学位プログラム名: 霊長類学・ワイルドライフサイエンス・リーディング大学院 / 京都大学 / 新制・課程博士 / 博士(理学) / 甲第24469号 / 理博第4968号 / 新制||理||1709(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 平田 聡, 教授 伊谷 原一, 教授 村山 美穂 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Mammal species often live in social groups, but the factors that promote group cohesion can be difficult to analyze due to the prevalence of strong group affiliations. Feral horses maintain stable harems of one or two males and several females, and harem stability is strongly related to individual fitness. Anecdotal evidence and an early study in the non-breeding season suggest that management of the Shackleford Banks island horses with immunocontraception reduces harem stability in the population, providing an opportunity to study the factors that influence harem stability. I investigated the effects of the immunocontraceptive PZP on harem stability during the breeding season and examined mare activity budgets and harassment rates to determine if these factors influence harem stability. I hypothesized that 1) immunocontraception would increase the rates at which mares changed harems during the breeding season 2) activity budgets of contracepted individuals would differ significantly from those of uncontracepted individuals, and 3) contracepted mares would experience greater levels of harassment associated with changing harems than uncontracepted mares. I found that the immunocontraceptive does increase harem changes during the breeding season. I also found that contracepted mares have different activity budgets than uncontracepted mares; as predicted, contracepted mares grazed less and moved more than uncontracepted controls. The factors that influence mare activity budgets included immunocontraception, harem stallion, number of individuals in the harem, number of mares in the harem and body condition of the mare, as well as some interactions between factors. I found that high harassment rates by both harem stallions and other mares in the harem are correlated with higher harem change rates and that contracepted mares are harassed more than uncontracepted mares. These results indicate that the immunocontraceptive does influence harem stability in this feral horse population, potentially through alterations in activity budgets and harassment rates.