Sexual Differences in Post-Hatching Saunders's Gulls: Size, Locomotor Activity, and Foraging Skill

Abstract

Various selection pressures induce the degree and direction of sexual size dimorphism in animals. Selection favors either larger males for contests over mates or resources, or smaller males are favored for maneuverability; whereas larger females are favored for higher fecundity, or smaller females for earlier maturation for reproduction. In the genus of Larus (seagulls), adult males are generally known to be larger in size than adult females. However, the ontogeny of sexual size dimorphism is not well understood, compared to that in adults. The present study investigates the ontogeny of sexual size dimorphism in Saunders's gulls (Larus saundersi) in captivity. We artificially incubated fresh eggs collected in Incheon, South Korea, and measured body size, locomotor activity, and foraging skill in post-hatching chicks in captivity. Our results indicated that the sexual differences in size and locomotor activity occurred with the post-hatching development. Also, larger males exhibited greater foraging skills for food acquisition than smaller females at 200 days of age. Future studies should assess how the adaptive significance of the sexual size dimorphism in juveniles is linked with sexual divergence in survival rates, intrasexual contests, or parental effort in sexes.

Response of young and adult birds to the same environmental variables and different spatial scales during post breeding period

“…Males and females may also respond to the same factors, but at different spatial scales (Alves et al 2013). There are some sexual differences in foraging tactics in gulls (Yoon et al 2013;García-Tarrasón et al 2015), which may results in differential response to spatial scales. However, in our study we did not control sex of birds as sex is indistinguishable in field conditions (Malling Olsen and Larsson 2004).…”

Genetic and morphological sex identification methods reveal a male-biased sex ratio in the Ivory Gull Pagophila eburnea

“…Although morphological differences can be marked between sexes in bird species, sexual dimorphism is often subtle in appearance or escape the human vision (Endler and Mielke 2005). Distinguishing males from females can be problematic in the field and methods have been developed to overcome this issue, including anatomical investigations (Miller et al 2007), vocalization analyses (Krull et al 2012), sex-specific behavior observations (Bosman et al 2012;Yoon et al 2013), and molecular techniques (Griffiths et al 1998;Fridolfsson and Ellegren 1999).…”

Tide Associated Incubation and Foraging Behaviour of Saunders's GullsLarus saundersi

“…a Reed bed of genus Phragmites) which allowed us to detect variation in the number of gulls in relation to tidal conditions. We also monitored the breeding stages of the nests found in this area during April-May 2011 (Yoon et al 2013) and April-May 2012: the average clutch size was 2.8 (n = 78 nests in 2011) and 2.7 (n = 61 nests in 2012) eggs per nest (mode = 3 eggs) at clutch completion, ranging from one to four eggs per nest. In 2011-2012, 64% of all monitored nests had at least one fledgling, as determined by the fledging behaviour of the semi-precocial chicks; nesting failure was mostly (43%) caused by nest predation (e.g.…”