The relationship between fertility and fat reserves of Peary caribou

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Abstract
There was a close association between pregnancy rates and levels of fat reserves and body weights in Peary caribou (Rangifer tarandus pearyi) collected in the late winters of 1974 through 1977 on several islands in the Canadian Arctic. Pregnancy rates were 2 years) females weighing 75% in those weighing >57 kg, and 100% in those >67 kg in weight. Pregnancy rates increased progressively from 7 to 100% as the percentage marrow fat increased from 43 to 79% and the kidney-fat index increased from 24 to 41%. Only heavy (>46 kg) yearling (21 month) females with high fat reserves were pregnant. Reproduction virtually ceased from 1973–1974 to 1975–1976 in Peary caribou on the western Queen Elizabeth Islands because their physical condition was poor. Pregnancy rates were as high as 100% in females in a second population located on Somerset and Prince of Wales islands, and in 1974–1975 four of five yearling females were pregnant. The adjustment of fertility to energy reserves is viewed as an adaptation to conserve energy. It is well developed in Peary caribou whose environment is characterized by a highly variable and often harsh climate in which negative energy balances probably prevail for 8 to 10 months of the year.

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