Assessing growth and age of Whiskered Tern Chlidonias hybrida chicks using biometrics

Abstract

The growth of Whiskered Tern Chlidonias hybrida chicks was investigated in Lake Grand-Lieu, western France. Body mass, tarsus, culmen and wing lengths of 33 chicks from 19 nests held in enclosures were measured at intervals of 2-3 days during the rearing period (0-20 days). The repeatability between two observers in chick body size measurements was generally high (overall 0.94), with the highest value for the wing length. Tarsus length and body mass increased fast and reached asymptotic values at about 14 (23.23 mm ± 0.18 SE) and 16 days (92.35 g ± 1.82 SE). The body mass growth rate (K, resulting from a logistic model) was 0.294 g day-1 ± 0.016. The linear growth rate at age 3-9 days was 6.32 g day-1 ± 0.28 SE. The standardized linear growth rate was 7.0% of adult body mass, which was in the range of values recorded for the closely related Black Tern Chlidonias niger (6.5-7.9%). The culmen and wing were still growing at fledging (age 20 days), asymptotic values had clearly not been reached. Before fledging, chicks were better aged by wing length (logistic model) than by any of the other body measurements. Given the geographic variation in bird morphometry, the applicability of our growth curves to disjoint populations of whiskered terns may be restricted. We encourage therefore new studies on chick growth in other European breeding populations.