Changes in body surface temperature play an under-appreciated role in the avian immune response

Fever and hypothermia are well characterized components of systemic inflammation. However, our knowledge of the mechanisms underlying such changes in body temperature is largely limited to rodent models and other mammalian species. In mammals, high dosages of an inflammatory agent (e.g., lipopolysaccharide, LPS) typically leads to hypothermia (decrease in body temperature below normothermic levels), which is largely driven by a reduction in thermogenesis, and not changes in peripheral vasomotion (i.e., changes in blood vessel tone). In birds, however, hypothermia occurs frequently, even at lower dosages, but the thermoeffector mechanisms associated with the response remain unknown. We immune-challenged zebra finches (Taeniopygia guttata) with LPS and monitored changes in subcutaneous temperature and energy balance (i.e., body mass, food intake), and assessed surface temperatures of, and heat loss across, the eye region, bill, and legs. We hypothesized that if birds employ similar thermoregulatory mechanisms to similarly-sized mammals, LPS-injected individuals would reduce subcutaneous body temperature and maintain constant surface temperatures when compared with saline-injected individuals. Instead, LPS-injected individuals showed a slight elevation in body temperature, and this response coincided with a reduction in peripheral heat loss, particularly across the legs, as opposed to changes in energy balance. However, we note that our interpretations should be taken with caution due to small sample sizes within each treatment. We suggest that peripheral vasomotion, allowing for heat retention, is an underappreciated component of the sickness-induced thermoregulatory response of small birds.