Photographic Key Determines Age and Gender in Two Thryothorus Wrens From Nicaragua's Pacific Slope
Forest Service scientists used meristics, or countable traits, plumage, and molt characteristics to derive an innovative photographic key for determining age and gender in two species of Neotropical wrens, Thryothorus rufalbus and T. modestus. The key is useful in determining age and gender, a daunting task throughout the species' range, but especially in the tropics, where few studies have been conducted.
Knowing a bird's age is an essential component of long-term avian banding programs designed to track changes in the demographics of Nearctic-Neotropical migrants and permanent residents, while monitoring their population trends. Plumage characteristics can be used to determine the gender, and much less often, the age of sexually dichromatic species that exhibit markedly different sizes and colors based on gender.
Avian sexual dichromatism is prominent in species with wide geographical ranges, and especially in those that undergo long-distance migration, whereas it is much less common in species with limited distribution and restricted movements. Neotropical wrens, which are members of the mostly New World family Troglodytidae, in general, tend to be sexually monochromatic (although seasonal sexual dichromatism occurs in some species). As a consequence, wrens pose a serious challenge to aging and sexing efforts.
To investigate the best techniques to confidently age and sex 2 permanent-resident wrens, the scientists captured 92 Rufous-and-white Wrens (Thryothorus rufalbus) and 61 Plain Wrens (T. modestus). They discovered that the gradation in the hues of the eumelanin, or black, pigment in the feather barbs of both species was lighter in young birds and can be used with confidence in aging but should be used in combination with molt limitsuthe boundaries between replaced and retained wing feathers during molting. Wing chord length, in combination with plumage characters and brood patch, are reliable criteria for determining the sex of Rufous-and-white Wrens.
Forest Service Partners