In conclusion
Lactating female striped hamsters kept at a relatively hot ambient temperature significantly decreased their energy intake and milk output during the peak of lactation, and raised significantly lighter offspring than those kept at a cooler temperature. Exposure to simulated wind significantly increased the energy intake and thermal conductance of hamsters lactating at a cooler temperature, but had no effect on milk output; results that support the PLH. However, consistent with the HDL hypothesis, the energy intake, milk output and capacity to dissipate heat of females at an ambient temperature of 32.5°C were all significantly increased by exposure to simulated wind. Moreover, lactating females kept at an ambient temperature of 21°C displayed a strong preference for sheltered conditions, whereas those kept at 32.5°C preferred simulated windy conditions. Wild, lactating female hamsters also appear to be more active on windy days in summer but on calm days in spring. Collectively, our results not only demonstrate the negative effects of high temperature on the maximum rate of energy intake and reproductive output, but also provide evidence that exposure to wind may improve milk production, and thereby the productivity and fitness, of small mammals during hot summer conditions.