Abstract
The growth of a nestling during the first few weeks after hatching is crucial for its further life and is sensitive to the conditions experienced during this period. Among species exhibiting Sexual Size Dimorphism (SSD), one of the most important factors influencing growth parameters is the sex of the hatchlings. In this study, we tested whether sex and other factors (hatching date, egg volume, brood size and sex ratio in the brood) were related to sex on growth parameters in Whiskered Tern (Chlidonias hybrida) chicks. In this species, males are 3%–10% larger than females when adult. At hatching, only the total head length was greater in males than females, but values close to fledging were greater for most of the measured parameters (3%—tarsus, 4%—total head length, 13%—body mass). Moreover, the maximum body mass growth rate was higher in males but females entered the rapid growth phase somewhat earlier and achieved the final total head length sooner. Nestling growth was also significantly correlated with brood size and hatching date, though mostly negatively (e.g. lower tarsus and total head length asymptote, lower maximum growth rate and growth rate constant of total head length in bigger and later clutches). The occurrence of SSD during the nestling period and higher maximum growth rate of body mass in males indicates that the costs of raising sons may be higher than of raising daughters. However, we did not find evidence of either sex-biased nestling mortality or skewed sex ratio.
Highlights
The early development of an individual bird affects its subsequent life in several ways, including competition for territory and mate as well as its fitness and survival (Lindström 1999; Metcalfe and Monaghan 2001)
The maximum growth rate in males was higher than in females, which means that males gain body mass faster than females (Tables 1, 2)
The mentioned above growth rate constant of the total head length was influenced by the interaction of the brood size and the sex of nestlings: females grew faster than males in two-chick broods, but there were no differences between the sexes in three-chick broods (Table 2)
Summary
The early development of an individual bird affects its subsequent life in several ways, including competition for territory and mate as well as its fitness and survival (Lindström 1999; Metcalfe and Monaghan 2001) This has long been of interest to ornithologists in view of the considerable variability in growth patterns among bird species (Ricklefs 1979; Richner 1991). We can perceive significant differences within a species in respect of chick growth parameters, depending on the conditions experienced by individual birds during this crucial period. In this regard, it is extremely important to identify factors influencing growth. Other related factors that influence chick growth include egg volume (Bogdanova and Nager 2008; Kalmbach et al 2009; rev. Krist 2011; DiazReal et al 2016), brood size (Müller et al 2005; Bogdanova and Nager 2008; Gilliland et al 2016), hatching date (Bogdanova and Nager 2008; Loonstra et al 2018), laying and hatching order (Müller et al 2005; Bosman et al 2016; Diaz-Real et al 2016), and sibling sex (Becker and Wink 2003; Müller et al 2005)
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