Marcin Przymencki, Klaudia Litwiniak, Magdalena Zagalska-Neubauer, Joanna Pomorska-Grochowska, Paweł Grochowski, Grzegorz Neubauer
Ornis Polonica 2023, 64: 107–118
https://doi.org/10.12657/ornis.2023.2.2
Abstract: Knowing the growth rate of chicks is important in ecological and evolutionary studies, since it allows to determine their age. In this article, we analysed the growth rate of chicks of the Caspian Gull Larus cachinnans for the first time for the species and we present a method of age estimation based on biometric measurements. The data were collected in 2005 and 2007 at Włocławek Reservoir (C Poland) and 2019–2020 at Mietków Reservoir (SW Poland). A total of 275 chicks were captured and ringed, and 150 of them were recaptured and measured more than once (in total 546 captures). During each capture, four biometric traits were taken: total head length (DCG), tarsus length (DT), bill height at the gonys (WD), and body mass (MA). Chicks’ average measurements at hatching were: DCG – 47 mm, DT – 24.2 mm, WD – 7 mm, MA – 55.1 g. These traits on the 35th day of chicks’ life, i.e. approximate fledging time, reached on average: DCG – 118.7 mm, DT – 76 mm, WD – 14 mm, MA – 994.7 g. DCG, WD, DT grew rather uniformly until reaching relatively stable asymptote, only the MA growth curve had a sigmoid shape. The average growth rate of traits (except WD) initially increased and then slowed down and was, respectively: DCG – 1.99 mm/day, with a peak on the 7th day of life (3.1 mm); DT – 1.44 mm/day, the highest increase was recorded on the 10th day of life (3.1 mm); WD – 0.2 mm/day, with a tendency to decline over time. Chicks’ MA was increasing exponentially until the 10th day of their life and the mean MA increase reached 26.1 g/day. The highest MA increase was recorded on the 16th day of chicks life (48.4 g/day). The data characterize the growth rate of Caspian Gull chicks and provide a valuable tool for estimating their age, and thus allow for more precise fieldwork planning in gull breeding colonies. This offers the possibility to reconstruct the approximate date of hatching and to obtain information on breeding phenology in a colony. The MS Excel spreadsheet with formulas for calculating the age of the chick based on the two most useful measurements in determining the age (DCG and MA) was made available for download (Appendix 1 to this work, at the www.ornis-polonica.pl website).
Keywords: ageing, Caspian Gull, chicks, growth rate, Larus cachinnans
