Generally speaking and watching the behaviour of these felines in the wild, we so far know that their reproduction season is between January and February. Nevertheless, this knowledge was not based on any scientific report, and researchers of Spanish National Research Council (CSIC) are pioneers in determining that the oestrogen concentration levels in the faeces of female lynxes are very low when they are sexually inactive. Usually, in January, there is an important increase in the concentration of these metabolites, which coincides with the ovulation cycle indicating the beginning of the female reproduction season. ’The variation in the faeces oestrogen concentration is so drastic –its increases up to five times- that it allows to accurately determine the exact moment of ovulation, as well as the beginning and end of adult female sexual activity’, Dr. Abáigar Ancín said. This method is specifically based on measuring the secondary metabolites found in the progesterone, testosterone and oestrogen contained in animal excrements. The ovaries are the organs that produce the hormones progesterone and oestrogen, whereas testosterone is the hormone produced by the testicles. Such hormones go from the reproductive organs to the bloodstream and then to the digestive system, from which they are expelled outside the body. Moreover, the receptivity period depends on many physiological, behavioural and environmental factors. In this sense, if a female does not mate or get pregnant, the high levels of oestrogen are kept until March or April so as to assure reproduction. Once the pregnancy ends, or from May if there is no pregnancy, the production of oestrogen hormones goes back to low levels until the next reproduction cycle in December. The end of puberty Another success of this project consists of determining the end of the puberty of the Iberian Lynx, that is, where he is no longer a cub, becomes an adult and therefore reaches sexual maturity. A hormonal analysis of testosterone and oestrogen in faeces carried out in a sample of cubs aged between eight and thirty six months revealed that the concentration levels were very low until they reached 22 months. From that age onwards, the presence of this hormone increases enormously until there is the hormonal cycle of an adult. ’The results until now are a magnificent tool for the managers of the Programa de Cría en Cautividad del Lince Ibérico (program on the breeding of the Iberian lynx in captivity)’, said Abáigar Ancín. The efforts that are currently made to assure the reproduction of this species show excellent results, and human intervention is very low. However, getting to know their reproduction cycle with accuracy is essential in order to perfect the assisted or artificial reproduction techniques that may be necessary for the future perpetuation of this species.