Journal
JOURNAL OF ORNITHOLOGY
Volume 162, Issue 4, Pages 1035-1047Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s10336-021-01911-y
Keywords
Chick growth; Sex-specific growth; Body mass; Body size; Sexual size dimorphism; Whiskered Tern; Sternidae
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Funding
- National Science Centre [2014/15/B/NZ8/00214]
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In Whiskered Tern chicks, males are generally larger and have a higher maximum growth rate than females, indicating that raising sons may be more costly than raising daughters. Nestling growth is also significantly affected by brood size and hatching date, with larger and later clutches generally showing lower growth rates.
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.
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