Effects of Supplemental Food on Snowshoe Hare Reproduction and Juvenile Growth at a Cyclic Population Peak

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Abstract
1. Snowshoe hare (Lepus americanus (Erxleben)) populations were provided with supplemental food on two study grids in the south-west Yukon to examine the effects of food on reproduction and juvenile growth. 2. Timing of parturition, pregnancy rates, litter sizes, male breeding condition, and juvenile growth rates were measured on two food grids and on two control grids during two summers at a cyclic peak in hare numbers. 3. Most female hares gave birth to three litters per summer, and parturition was in approximate synchrony, such that there were three distinct litter groups per season. 4. The main effects of food addition were to increase hare densities 2.1-to 2.7-fold, advance the timing of breeding by about 1 week in 1 year, and increase pregnancy rates by 5% relative to the controls. 5. There were no significant differences in litter sizes, lengths of male breeding seasons, juvenile growth rates, or total female reproductive output between hares on the food and control grids. 6. Third litter stillborn rates were higher, and third litter juvenile growth rates slightly lower on food grids relative to those on controls, possibly reflecting an effect of higher densities. 7. This study suggests that food is not a proximate factor limiting hare reproduction and early juvenile growth at the observed peak hare densities.

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