Which of the following options best describes the thermal response of animals when they are too cold?

The thermal response of animals when they are too cold involves physiological adaptations aimed at conserving heat and maintaining body temperature. The best description is increased metabolism to produce heat. When animals are exposed to cold temperatures, their bodies react by raising metabolic rates. This increase in metabolism generates additional internal heat, helping to warm the body and maintain core temperature.

This response is crucial for survival in colder environments, as it counteracts the heat loss that occurs due to low ambient temperatures. Animals may also engage in behaviors such as seeking shelter or clustering together for warmth, but from a physiological standpoint, boosting metabolism is a primary response to cold exposure.

The responses are aimed at reducing heat loss and ensuring that body functions remain efficient in colder conditions. The other options suggest mechanisms that do not support the body’s need to conserve heat in cold environments. For example, increased blood flow to the skin would promote heat loss rather than conservation, while increased sweating relates to cooling, and decreased blood flow from capillaries does not directly contribute to generating body heat.