Pairing in 141 pairs of Pinyon Jays (Gymnorhinus cyanocephalus ) was assortative for age, but was random for bill length and body weight. Assortative pairing for age may be favored because similar-aged partners produced slightly more young than dissimilar-aged ones and their young survived longer than young from dissimilar-aged pairs. Large jays appear to have the highest genetic quality because they lived longer and body size was heritable. Genetic quality of a mate, however, may be negated if phenotypic properties of partners are not compatible
