Vasoconstriction occurs when the arteriovenous shunts dilate. This causes less blood to flow through the capillaries near the surface of the skin.Sweating is decreased to reduce evaporative cooling. The erector pili muscles contract raising hairs or feathers. This traps a layer of insulating air next to the skin reducing heat lost to the environment.The body may begin to shiver. Rapid involuntary contractions of large (voluntary) muscles in the body generate heat by respiration.