Relationship between wing length and body mass in Atlantic Puffin chicks

Ages of Atlantic Puffin (Fratercula arctica) chicks are sometimes estimated by comparing their wing lengths with a sample of known-aged chicks from the same colony. The technique is reliable if the rare of wing growth is unaffected by variation in nutrition. Recent studies suggest that wing growth may respond to food supply. I investigated variation in wing length in relation to chick age and mass during a period of reduced food availability. Wing length was correlated with mass at all chick ages, and wing growth over a 4-d interval was related to change in mass over the same interval at most ages. Variation in wing length and differences between estimated and actual ages increased with age. Average ages of chicks between 5-50-d old were estimated satisfactorily, but estimates for chicks growing faster or slower than average were biased. Measurements from a representative sample of contemporary, known-aged chicks are required to provide reliable, average age estimates. Large potential errors for individual chicks poses problems for studies investigating individual behavior.