The Ruby-throated Hummingbird (Archilochus colubris), as the only species of hummingbird found in eastern North America, has drawn the attention of naturalists for decades. Its high rate of energy expenditure, remarkable flight dynamics, and iridescent colors are shared with several other members of the family found in the southwestern United States and Central America. The nesting habits of this species have been observed and recorded by naturalists but nesting has not been critically examined in attempts to analyze the energetics involved. In this article, I deal with some aspects of incubating egg temperatures.