Jongmin Yoon

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

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 Saunderss 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.

Nest predation risk influences a cavity-nesting passerine during the post-hatching care period

Some nest predators visually assess parental activities to locate a prey nest, whereas parents modify fitness-related traits to reduce the probability of nest predation, and/or nestlings fledge early to escape the risky nest environment. Here, we experimentally tested if the parental and fledging behaviours of oriental tits (Parus minor) that bred in the nest-box varied with cavity conditions associated with nest predation risk during the nestling period. The entrance of experimental nest-boxes was enlarged to create a long-term risk soon after clutch competition. A short-term risk, using simulated playbacks with a coexisting control bird and avian nest predator sound, was simultaneously applied to the nest-boxes whether or not the long-term risk existed. We found that the parents reduced their hourly feeding trips, and the nestlings fledged early with the long-term risk, although the nest mortality of the two nest-box types was low and did not differ. While this study presents a portion of prey–predator interactions with the associated uncertainties, our results highlight that the entrance size of cavities for small hole-nesting birds may play an important role in determining their fitness-related traits depending upon the degree of perceived risk of nest predation.

Post-Mating Sexual Behaviors of Oriental Storks (Ciconia boyciana) in Captivity

Parental behaviors that vary by sex and breeding stage facilitate the survival of offspring in birds. Females invest in reproducing according to the level of direct and/or indirect benefits provided by males. Males face trade-offs from defending territories or nests, providing for the young, and seeking additional mating opportunities. We examined whether post-mating sexual behaviors such as courtship display and nest-building were associated with reproductive investments made by males and females in the current study. The oriental stork (Ciconia boyciana) is known as a solitary breeder that nests in tall trees and provides biparental care with long post-hatching development. We filmed parental behaviors in seven stork pairs in captivity for 655 hours (245 hours during nest-building, 218 hours during incubation, 328 hours during nestling, and 192 hours during the fledgling period). We found that paired mating behaviors such as synchronous allopreening and bill-clattering were highly skewed to the pre-incubation period. Males participated in nest-building more than females although both sexes shared similar parental care during the incubation and nestling period. Male nest-building was negatively correlated with male nest attentiveness only during the nestling period. Our results suggest that male oriental storks with higher nest-building effort might spend more time taking precautions against conspecific intruders or nest predators near the nests with chicks while the females were attending the nests in the form of biparental care.

Parent recognition in chicks of the ground-nesting, nidifugous Saunders's Gull Saundersilarus saundersi

Abstract. In birds, offspring-parent interactions play an essential role in facilitating offspring survival at nest-leaving. In contrast to nidicolous nestlings, nidifugous chicks are expected to hatch in ground nests, leave the nest soon after hatching, and presumably exhibit precise parent-offspring recognition during this time. Yet, some studies document variation in nidifugous behavior and offspring-parent recognition of semi-precocial chicks during the nest-leaving stage in the family Laridae. We examine patterns in nest-leaving age, mobile capacity, and parent recognition in wild and captive chicks of the Saunderss Gull Saundersilarus saundersi that is one of ground nesting and colonially breeding species. Our results indicated that the development of locomotor activity in nidifugous chicks coincided with the nestleaving age. Soliciting behavior of experimental chicks increased with age, but they strongly discriminated vocalizations of pseudo-parents against unfamiliar adults only at the early stage of nest-leaving. We suggest that parent recognition by chicks during this short period may play a key role in facilitating their own survival while moving to a new environment with their parents after leaving the nest. More studies using a comparative approach are needed to understand how nesting ecology, nest-leaving behavior, and parent-offspring interaction are interconnected in the members of the family Laridae.

Does Nest Predation Influence Colony Movements of Saunders's Gulls (Saundersilarus saundersi) in a Reclaimed Land Area?

Some seabirds commonly use artificially reclaimed lands, which are frequently located next to mainland environments, for breeding. Nest predation risk caused by birds or mammals from the mainland has negative influence on fitness-related costs and distribution of seabirds. Here, we sought to link potential factors, specifically those related to nest predation and nest environment, with breeding performance and colony movements of the Saunderss gull (Saundersilarus saundersi), a vulnerable species, on a large reclaimed area (1350 ha) in Incheon in Republic of Korea. This reclaimed area has experienced rapid changes in communities of nest predators from the mainland and vegetation ranging from halophytes to terrestrial plants after reclamation. Additionally, changes in the surrounding of used nest sites were retrospectively examined to determine whether colony movement was reversible in this reclaimed area. Our results indicated that high nest predation in a previous year induced colony movements in a consecutive year while the breeding colony exhibited a gradual reduction in clutch size. However, such movement after high nest predation seemed to be irreversible due to ongoing habitat degradation caused by construction and vegetation alteration. This study highlights that high nest predation may exert strong pressure on breeding colonies of Saunderss gulls. It also has anthropogenic impacts, leading to continuous dispersal of colonies to new areas for this vulnerable seabird in a reclaimed land.

Tide Associated Incubation and Foraging Behaviour of Saunders's Gulls Larus saundersi

Various factors such as food, climate, nest predation, and phylogenetic relationships influence parental behaviour in birds. However, few studies have addressed how the tidal cycle shapes incubation behaviour in seabirds. In the intertidal zone, spatiotemporal limitations in foraging opportunities for the parents are expected to affect breeding behaviour. We studied tide-associated incubation behaviour in Saunderss Gulls Larus saundersi, nesting in a colony on recently reclaimed land and foraging on tidal mudflats, near Incheon in the Republic of Korea. This colony is the last remaining colony in the Republic of Korea. In May 2012, the number of non-foraging adults present in the 200 ha nesting area was monitored; also parental activity at ten nests was videotaped during the daytime, using a car black box recording system. Presence in the colony and parental activity were analysed in relation to the tidal cycle, ambient temperature, time of day, and nesting success. Our results indicated that the number of non-foraging adults staying in the nesting area was higher at high tide than at low tide, and the time that parents incubated eggs increased with higher sea level. The observed pattern was more apparent during ebb tide than during flood tide. No association of time of day, ambient temperature, and nesting success was found. We conclude that the parents regulate incubation in response to the exposure time of their foraging areas and possibly the dietary activity of benthic organisms in the mudflats.

Use of the foraging area by captive bred oriental storks (Ciconia boyciana) in a closed semi natural paddy field

Rice paddy fields have been recognized as an alternative habitat for avian wetland foragers, and fish-rice farms have become a new tool in improving the abundance of aquatic animals. However, the use of the habitats by avian foragers, particularly by oriental storks (Ciconia boyciana), was not well understood. In the present study, we investigated how a fish-rice farm influenced the abundance of aquatic animals and documented the foraging behavior of the two captive bred oriental storks in a closed semi-natural paddy field. Our results showed that the fish refuge pond (water depth 40 cm) had a higher abundance of fish whereas the areas planted with rice (water depth 20 cm) had more tadpoles and some aquatic insects. The two captive bred oriental storks captured mostly fish and aquatic insects in the rice-planted area and mostly fish in the fish refuge pond. The two oriental storks had higher foraging success and spent more time for foraging in the rice-planted area than in the fish refuge pond. This result suggests that the oriental storks might prefer foraging in the area with fish, aquatic insects, and amphibians under a greater success rate presumably due to shallow water depth in the paddy fields with a fish-rice farm.