Antler Mass of Barren-Ground Caribou Relative to Body Condition and Pregnancy Rate

Abstract

ABSTRACT. Antlers of caribou (Rangifer tarandus) likely contribute to breeding success of males, defence of feeding sites by females, and recognition of the hierarchical status of conspecifics. However, few data are available on how antler mass is related to age, body mass, fat reserves, other physical indices, and reproduction. Mass of antlers was recorded for 958 caribou obtained in early and late winter, 1982 through 1987, from the Beverly herd of barren-ground caribou (R. t. groenlandicus) in north-central Canada. In females, antler mass increased with age to 14 years, whereas mean body mass was stable from 7 through 13 years. Female antler mass correlated with body mass, body size, fat indices, and pregnancy rate both among and within age classes. In males, antler mass correlated highly with lean body mass to age 4 years. Antler mass varied among years in concert with fatness in females and with changes in body mass in both sexes. We conclude that antler mass is an index of body mass, body size, condition, and pregnancy rate, but high variation makes it inferior to other indices.Key words: antler and body mass, Arctic, Subarctic, fat indices, pregnancy rate, Rangifer tarandus RÉSUMÉ. La ramure du caribou (Rangifer tarandus) contribue probablement au succès de la reproduction chez le mâle, à la défense des aires d'alimentation chez la femelle et à la reconnaissance du statut hiérarchique parmi les congénères. On possède toutefois peu de données sur la façon dont le poids de la ramure est relié à l'âge, à la masse corporelle, aux réserves de gras, à d'autres indices physiques et à la reproduction. On a consigné le poids des ramures pour 958 caribous prélevés au sein de la harde Beverly de caribous des toundras (R. t. groenlandicus) dans le centre-nord du Canada, au début et à la fin de l'hiver, de 1982 à 1987. Chez la femelle, le poids de la ramure augmentait avec l'âge jusqu'à 14 ans, alors que de 7 à 13 ans, la moyenne de la masse corporelle était stable. Chez la femelle, le poids de la ramure était en corrélation avec la masse corporelle, la taille du corps, les indices de gras et le taux de gestation entre les groupes d'âge et au sein de ces groupes. Chez le mâle, le poids de la ramure était fortement corrélé avec la masse corporelle maigre jusqu'à l'âge de 4 ans. Le poids de la ramure variait d'une année à une autre de concert avec l'adiposité chez la femelle, et de concert avec les changements dans la masse corporelle chez les deux sexes. On conclut que le poids de la ramure constitue un indice de la masse corporelle, de la taille du corps, de l'état corporel et du taux de gestation, mais que sa grande variation en fait un indice inférieur à d'autres.Mots clés: ramure et masse corporelle, Arctique et Subarctique, indices de gras, taux de gestation, Rangifer tarandus Traduit pour la revue Arctic par Nésida Loyer.

Svalbard reindeer (Rangifer tarandus platyrhynchus) antler characteristics reflecting the local environmental conditions

“…On this basis, the antler characteristics in reindeer populations have been recognised as a proxy of the population conditions, with certain limitations discussed later. Similar conclusion has also been reported by Thomas and Barry (2005) using the antler mass as a proxy of conditions for each individual.…”

“…The antler size seems obviously dependent on age, too. There has been observed an overall positive correlation between age and antler size (Thomas and Barry, 2005), with the maximum antler size at an age of about 14-16 years. Therefore, our results reflect both the population fitness and the population age structure.…”

Non-Invasive Assessment of the Interrelationships of Diet, Pregnancy Rate, Group Composition, and Physiological and Nutritional Stress of Barren-Ground Caribou in Late Winter

“…Pregnancy is largely a factor of autumn weight/body condition [26,27,51]. Pregnancy rate (95% confidence interval = 76–88%) was slightly lower than what would be expected for a healthy, increasing herd (~90%) [44,52–54]. Given the Western Arctic Herd’s high population size and decade-long decline, the lower pregnancy rate is not unexpected [27,55].…”

Morphological change in Newfoundland caribou: Effects of abundance and climate

“…The inability of the GLM models to account for decreased antler size may reflect the current nutritional conditions for males (i.e., conditions in year of harvest) rather than conditions in the year of birth. In elk, for example, antler mass appears indicative of prevailing foraging conditions while they are growing (Smith, 1998) and in male caribou, antler mass (but not the number of tines) varies in concert with body mass (Markusson & Folstad, 1997;Thomas & Barry, 2005). In addition, overgrazing may have created foraging conditions that are a cumulative result of past foraging activity and not directly related to current population abundance or climate conditions (Henry & Gunn, 1991).…”

“…In sum, our study points to diminished body size, in these and other large insular Newfoundland herds (Mahoney, 2000;Mahoney & Schaefer, 2002; S. Mahoney and J. Schaefer, unpublished data), as a phenotypic consequence of high abundance and large-scale climate patterns, likely mediated by nutrition. Jawbone size and antler or horn quality are highly sensitive to variation in nutrient quality and availability (Suttie & Kay, 1982;Suttie & Mitchell, 1983;Gordon et al, 2004;Høye & Forchhammer, 2006) and are frequently used as proxies of range quality and condition (Nugent & Frampton, 1994;Hewison & Gaillard, 2001;Schmidt et al, 2001;Keyser et al, 2005;Thomas & Barry, 2005;Weladji et al, 2005;Høye & Forchhammer, 2006). Beyond morphology, other ecological features of Newfoundland caribou coincide with their dramatic numerical fluctuations.…”