North American Bird Bander Jan-Mar 2015 Vol. 40 No. 1

Feature Articles

The Accuracy of Eastern Bluebird (Sialia sialis) Nestling Age Estimates Produced from Three Different Aging Guides of Digital Images

Nikki Wilkins and William P. Brown

Abstract- We examined the accuracy of age estimates produced from three different aging guides of Eastern Bluebird (Sialia sialis) nestlings.  The “complete guide presented digital images of dorsal and lateral views of the entire nestling from days 1 to 17 after hatching.  The “wing” aging guide presented images of lateral views of wings and the “tail” aging guide presented dorsal views of tails for the same span of development.  One of the three aging guides and one of 16 sets of 50 randomly selected images from a total of 596 images were assigned randomly to each participant (n= 39) participants resulting in 1,950 age estimates.  Differences in average daily age estimates among the guides were explored with a linear mixed model with each observer specified as a random variable.  Differences in overall accuracy (± 1 day of actual nestling age) among the three guides are differences in the proportion of accurate age estimates for each day of development among the guides were evaluated with corrected Chi-square tests.  There were no differences in average daily age estimates among the three guides but overall accuracy differed among the guides (p <0.001). Estimates generated by the complete guide (90.3% accurate) did not differ from those of the wing guide (88.2% accurate).  Age estimates from the complete and wing guides differed from those generated with the tail guide (75.1% accurate).  Generally, the proportion of accurately determined age estimates decreased for older nestlings.

Eye Coloration in Common Yellowthroat (Geothlypis trichas) to Determine Age

Gerardo Rodriguez Ramos, Manuel Grosselet and Georgita Ruiz

Abstract- We present a study on age determination of the Common Yellowthroat (Geothlypis trichas) through the use of eye coloration, which is compared with other known aging criteria: skull ossification, preformative molt and shape of rectrices.  From a sample of 300 birds, it has been determined that the use of eye color is one of the most reliable criteria to determine the age of this species during fall.  It is recommended that one gains experience observing captured birds to establish the characteristic.