Body size relationships and reproductive ecology of female feral horses on Sable Island, Nova Scotia
Date
2015-04-17
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Masters
Abstract
Body size is an important determinant of reproduction in capital breeding animals, including
large mammals. However, it is not always practical to hand-measure body size of free-ranging
species. In recent years, parallel-laser photogrammetry has been used to obtain remote estimates
of body size for some animals, though it remains unknown how well this technique might
capture variation in curvilinear body features or if the distance between parallel-laser calipers is
altered when projected onto a curved surface. In this thesis, I describe a photogrammetric system
that may be useful for obtaining body-size measurements from unrestrained large mammals that
permit approach, using domestic horses (Equus ferus caballus) as a model (Chapter 2). I then
apply this technique in the field to a wild (feral) population of horses at Sable Island National
Park Reserve, Nova Scotia, Canada, where I include body size measurements as variables in a
detailed analysis of factors affecting reproduction in females (Chapter 3). Using my parallel-laser
photogrammetric system, I show how curvilinear hand-measurements (e.g., across the barrel of a
horse) are stongly correlated with their respective linear photogrammetric estimates (R2 ≥ 0.998),
and most photogrammetric estimates using my system had high reliability. Using three variables
of body size, photogrammetric estimates and hand-measurements explained 86.0% and 96.2%,
respectively, of the variation in body weight of a sample of domestic Newfoundland ponies. On
Sable Island, Nova Scotia, I examined the relationship of numerous variables (including skeletal
body size and body condition) with the probability of yearly reproductive success for female
Sable Island horses (years 2008–2012), where I define reproductive success as production of an
offspring surviving to one year of age. Age class was a dominant factor predicting reproductive
success, as expected from trends previously associated with body size or reproductive experience
iii
in other populations. Age-class specific energy budgets or social and sexual behaviour caused a
more pronounced relationship with body condition at parturition in sub-adults, and body
condition at conception and stability of consort relationships were associated with reproductive
success in adults. In addition, relationships with local density suggested limited forage around
the time of conception and limited water during lactation might also influence reproductive
success in adult females. Although relationships were evident for age class, which is correlated
with body size, reproductive success was not related to skeletal body size, past reproductive
experience, age of primiparity, or band structure. The capital breeding strategy and year-round
social associations seen in horses make their reproductive ecology a combination of patterns
observed for large ungulates and social primates.
Description
Keywords
body size, conformation, Equus ferus caballus, horse, morphometrics, parallel-laser calipers, photogrammetry, Sable Island, reproductive ecology, reproduction, density, age, socio-ecology, body condition, reproductive success, weather
Citation
Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology