Abstract: Steroid hormone testosterone is one of the most important sex hormones affecting bird reproduction, which is closely related to breeding behavior. Testosterone affects sexual selection by changing feather color, song and so on. Meanwhile, testosterone could regulate the tradeoff between sexual selection and reproductive input. Testosterone affects reproductive efficiency, including nestling size, fledging size, and hatching success rate. Testosterone also affects the immune activity and survival rate of individuals. Most studies of bird breeding are based on exogenous implantation of testosterone. The results from literature had no consensus. The changes of testosterone level under natural conditions and the influencing factors are not well understood. The effects of testosterone on the reproductive process differed between male and female birds. Further studies on the effect of testosterone on breeding birds are critically needed.

Key words: microbial enhanced oil recovery, denitrifying bacteria, oil swelling, nitrous oxide