Sources of variation in measurements of birds in a Puerto Rican dry forest

Abstract

Based on more than 2000 total captures of 40 species of birds in 14 avian families, resulting from 15 yr of banding at a single net line in southwestern Puerto Rico, body mass and wing length measurements of 246 individuals of 25 species of birds that were captured and recaptured 612 times were used to show that: (1) Among and within different individuals, temporal variation in selected avian morphological characters is minimal when measurements are taken at the same time of year. (2) Measuring instruments widely used in the field are precise. (3) Sampling techniques are comparable. (4) Investigator influence, for single and cooperative banders, is minimal even when small samples are compared. Seasonal and daily variation within the data did appear, however, and were attributed to seasonal fluctuations of food resources, feather wear, breeding activities, and the added mass of ingested food. These data emphasize that the time of measurement is a critical factor when comparing morphological measures among different studies. Comparing measures from one season with those from another, or comparing measures taken during a whole year with those taken during a brief period, may show differences that are not biologically significant.

Citation

Arendt, Wayne J.; Faaborg, John. 1989. Sources of variation in measurements of birds in a Puerto Rican dry forest. Journal of Field Ornithology 60:1–11.