Experimental evidence that hyperthermia limits offspring provisioning in a temperate-breeding bird

In many vertebrates, parental care can require long bouts of daily exercise, that can span several weeks. Exercise, especially in the heat, raises body temperature, and can lead to hyperthermia. Typical strategies for regulating body temperature during endurance exercise include modifying performance to avoid hyperthermia (anticipatory regulation hypothesis) and allowing body temperature to rise above normothermic levels for brief periods of time (facultative hyperthermia hypothesis). Facultative hyperthermia is commonly employed by desert birds to economize on water, but this strategy may also be important for chick-rearing birds to avoid reducing offspring provisioning when thermoregulatory demands are high. In this study, we tested how chick-rearing birds balance their own body temperature against the need to provision dependent offspring. We experimentally increased the heat dissipation capacity of breeding female tree swallows (Tachicyneta bicolor) by trimming their ventral feather...