Sexual differences in post-hatching Saunders's gulls: size, locomotor activity, and foraging skill

Area of Science:

• Zoology
• Evolutionary Biology
• Animal Behavior

Background:

• Sexual size dimorphism (SSD) is common in animals, driven by varied selection pressures on males and females.
• In the genus Larus (seagulls), adult males are typically larger than females, but juvenile SSD ontogeny is less understood.
• Saunders's gulls (Larus saundersi) present a model for studying the development of SSD.

Purpose of the Study:

• To investigate the ontogeny of sexual size dimorphism in Saunders's gulls (Larus saundersi) under controlled, captive conditions.
• To analyze the development of sexual differences in body size, locomotor activity, and foraging skills in juvenile gulls.
• To explore the early life-stage emergence of SSD and its potential adaptive significance.

Main Methods:

• Artificial incubation of collected Saunders's gull eggs from Incheon, South Korea.
• Post-hatching monitoring of chicks in captivity, measuring body size, locomotor activity, and foraging proficiency.
• Comparative analysis of sexual differences throughout juvenile development.

Main Results:

• Sexual differences in body size and locomotor activity were observed to develop progressively after hatching.
• By 200 days of age, larger male gulls demonstrated superior foraging skills compared to smaller female gulls.
• The study identified distinct developmental trajectories for size and behavior between sexes in juvenile gulls.

Conclusions:

• Sexual size dimorphism in Saunders's gulls originates and develops during the post-hatching juvenile phase.
• The observed differences in size and foraging skills suggest early adaptive divergence between sexes.
• Further research is needed to link juvenile SSD with survival rates, competition, and parental investment.