Eurasian Oystercatchers Haematopus ostralegus have proven indicators and play important roles as top predators of coastal ecosystems. Eurasian Oystercatcher Haematopus ostralegus has proven indicator and play important role as top predator of coastal ecosystem. There are four subspecies of Eurasian ...
Eurasian Oystercatchers Haematopus ostralegus have proven indicators and play important roles as top predators of coastal ecosystems. Eurasian Oystercatcher Haematopus ostralegus has proven indicator and play important role as top predator of coastal ecosystem. There are four subspecies of Eurasian Oystercatcher: Haematopus ostralegus osculans is the subspecies that live in the East Asia have been designated as the Natural Monument No. 326 and the Endangered Wild Species Class Ⅱ in Korea. Because the great majority of the studies about H. o. osculans in Korea have focused in wintering populations until now, there is little detailed studies of H. o. osculans foraging behavior.
This study has been conducted on H. o. osculans foraging behavior in Yubu Island large numbers wintering during the breeding season. Study area is the three deserted islands and tidal flats about 2㎞ north of Yubu Island. When the breeding season has come in earnest, late March to late June, I visited the breeding sites to find the nests every two to three days a week. If the nests were confirmed incubation from egg surface temperature, the nests were considered active and were checked to determine whether the chicks had hatched. If the eggs failed before hatching, I tried to determine the causes of hatch failure: predated, washed away, broken, unhatched, abandoned.
The individuals started foraging behavior were randomly selected for video recording as close to the individuals as possible. The recording time for each individual was 3.12±0.10min(mean±SE, n=115). The recorded videos were analyzed using slow mode and repeat mode replay walk, prey search, prey swallow(No./recording time). The prey search of H. o. osculans was classified single peck, multiple peck, boring. Analysis of video recordings allowed the distinction among prey items or observation part of body from foraging process, prey items were classified gastropod, polychaeta, bivalve, crustacean. I compared how the factors: ⅰ) breeding stage(pre-incubation, incubation, brood-rearing, fledging), ⅱ) foraging site type(tide line, nearby nest site), ⅲ) age(adult, immature), ⅳ) tidal cycle: affects foraging behavior, prey swallow and prey items. As foraging specialization, individuals of which eat only one, has been observed through the recorded videos, I compared how prey items would cause any difference foraging behavior and prey swallow. In addition, I measured handling time, a prey item until it was searched and swallowed, and head ups, the number of times the head was raised thile a prey item was handled. Significant test was followed by Mann-Whitney U test, Kruskal-Wallis ANOVA test and Spearman's rank correlation as nonparametric statistical analysis.
A total of 148 nests in Yubu Island during the breeding season combined 2015 and 2016 were identified. Most nests were created in April, clutch size topped three(56.76%). The average hatching success rate of 132 eggs hatch confirmed or presumed were 30.96±3.50%. The main cause of 240 eggs hatch failed is predated by 37.18±3.72%, which is presumed due to Black-tailed Gulls Larus crassirostris or mammals. Especially, Black-tailed Gulls are invisible before entering into the breeding site but appear as soon as entering, they are witnessed to fly approach. The eggs predated of rate at Site B was about half that of other sites. According to previous studies, sandy areas with gentle slopes, low height and open squares are advantageous for easy monitoring of predators, the predation rate is relatively low. However, it is necessary to execute the survey method using video recording in order to investigate accurate predation status.
At early of the breeding season, gastropod Umbonium thomasi account for about 92% of the foraging prey items for H. o. osculans. It gradually decreased over time and only about 27% the breeding was completed. By contrast, at early of the breeding season, bivalve account for about 7% of the foraging prey items for H. o. osculans but increased to 70% later. Although to eat much for a short time at early of the breeding season, H. o. osculans choose gastropod Umbonium thomasi using single peck, by choosing bivalve as a prey item using multiple peck and boring at the late of the breeding season, prey swallow gradually increased. Because bivalve clearly is larger compared with other prey item and dominates benthic invertebrates biomass, H. o. osculans follow the tide line must be an efficient prey item. In order to verify the difference in foraging trends according to the breeding stage, studies on biomass change between gastropod Umbonium thomasi and bivalve must be promoted preferentially. Polychaeta account for about more than 80% of the foraging prey items in the nearby nest site as drained foraging site type. Also, it captured about 43%, highest level in brood-rearing stage. This was utilize the foraging site closest the nest site to protect cheek, the reason choice polychaeta as main prey item might be polychaeta activity increased during the tide retreats all surface water is drained. Despite a lot of walk, more prey search compared to the tide line, result prey swallow was lower supporting that the nearby nest site is not a good foraging site.
Although immature often used boring more energy than adult, there is no difference foraging behavior, prey swallow and prey items overall. It was showed the younger foraging ability was not fall necessarily. Foraging ability in younger increased by experiencing which had probably fed with other individuals. Depending on tidal cycle, most foraging behavior and prey swallow could not be confirmed significant difference, but there was a significant difference in prey items. Unlike gastropod Umbonium thomasi, the frequency of foraging bivalve gradually decreased from high tide to ebb tide. Sometimes H. o. osculans was observed to be taken from the surface of sand at high tide. In order to satisfy the energy demand required for H. o. osculans, it is considered foraging of bivalve is necessarly performed.
H. o. osculans population in Yubu Island clearly increased the foraging specialization using both tide line and nearby nest site to forage, but it is uncertain how it affects the long-term fitness of the population. I'm convinced continuous foraging study at the individual level can be quite useful for formulating an effective conservation strategy for H. o. osculans.
Eurasian Oystercatchers Haematopus ostralegus have proven indicators and play important roles as top predators of coastal ecosystems. Eurasian Oystercatcher Haematopus ostralegus has proven indicator and play important role as top predator of coastal ecosystem. There are four subspecies of Eurasian Oystercatcher: Haematopus ostralegus osculans is the subspecies that live in the East Asia have been designated as the Natural Monument No. 326 and the Endangered Wild Species Class Ⅱ in Korea. Because the great majority of the studies about H. o. osculans in Korea have focused in wintering populations until now, there is little detailed studies of H. o. osculans foraging behavior.
This study has been conducted on H. o. osculans foraging behavior in Yubu Island large numbers wintering during the breeding season. Study area is the three deserted islands and tidal flats about 2㎞ north of Yubu Island. When the breeding season has come in earnest, late March to late June, I visited the breeding sites to find the nests every two to three days a week. If the nests were confirmed incubation from egg surface temperature, the nests were considered active and were checked to determine whether the chicks had hatched. If the eggs failed before hatching, I tried to determine the causes of hatch failure: predated, washed away, broken, unhatched, abandoned.
The individuals started foraging behavior were randomly selected for video recording as close to the individuals as possible. The recording time for each individual was 3.12±0.10min(mean±SE, n=115). The recorded videos were analyzed using slow mode and repeat mode replay walk, prey search, prey swallow(No./recording time). The prey search of H. o. osculans was classified single peck, multiple peck, boring. Analysis of video recordings allowed the distinction among prey items or observation part of body from foraging process, prey items were classified gastropod, polychaeta, bivalve, crustacean. I compared how the factors: ⅰ) breeding stage(pre-incubation, incubation, brood-rearing, fledging), ⅱ) foraging site type(tide line, nearby nest site), ⅲ) age(adult, immature), ⅳ) tidal cycle: affects foraging behavior, prey swallow and prey items. As foraging specialization, individuals of which eat only one, has been observed through the recorded videos, I compared how prey items would cause any difference foraging behavior and prey swallow. In addition, I measured handling time, a prey item until it was searched and swallowed, and head ups, the number of times the head was raised thile a prey item was handled. Significant test was followed by Mann-Whitney U test, Kruskal-Wallis ANOVA test and Spearman's rank correlation as nonparametric statistical analysis.
A total of 148 nests in Yubu Island during the breeding season combined 2015 and 2016 were identified. Most nests were created in April, clutch size topped three(56.76%). The average hatching success rate of 132 eggs hatch confirmed or presumed were 30.96±3.50%. The main cause of 240 eggs hatch failed is predated by 37.18±3.72%, which is presumed due to Black-tailed Gulls Larus crassirostris or mammals. Especially, Black-tailed Gulls are invisible before entering into the breeding site but appear as soon as entering, they are witnessed to fly approach. The eggs predated of rate at Site B was about half that of other sites. According to previous studies, sandy areas with gentle slopes, low height and open squares are advantageous for easy monitoring of predators, the predation rate is relatively low. However, it is necessary to execute the survey method using video recording in order to investigate accurate predation status.
At early of the breeding season, gastropod Umbonium thomasi account for about 92% of the foraging prey items for H. o. osculans. It gradually decreased over time and only about 27% the breeding was completed. By contrast, at early of the breeding season, bivalve account for about 7% of the foraging prey items for H. o. osculans but increased to 70% later. Although to eat much for a short time at early of the breeding season, H. o. osculans choose gastropod Umbonium thomasi using single peck, by choosing bivalve as a prey item using multiple peck and boring at the late of the breeding season, prey swallow gradually increased. Because bivalve clearly is larger compared with other prey item and dominates benthic invertebrates biomass, H. o. osculans follow the tide line must be an efficient prey item. In order to verify the difference in foraging trends according to the breeding stage, studies on biomass change between gastropod Umbonium thomasi and bivalve must be promoted preferentially. Polychaeta account for about more than 80% of the foraging prey items in the nearby nest site as drained foraging site type. Also, it captured about 43%, highest level in brood-rearing stage. This was utilize the foraging site closest the nest site to protect cheek, the reason choice polychaeta as main prey item might be polychaeta activity increased during the tide retreats all surface water is drained. Despite a lot of walk, more prey search compared to the tide line, result prey swallow was lower supporting that the nearby nest site is not a good foraging site.
Although immature often used boring more energy than adult, there is no difference foraging behavior, prey swallow and prey items overall. It was showed the younger foraging ability was not fall necessarily. Foraging ability in younger increased by experiencing which had probably fed with other individuals. Depending on tidal cycle, most foraging behavior and prey swallow could not be confirmed significant difference, but there was a significant difference in prey items. Unlike gastropod Umbonium thomasi, the frequency of foraging bivalve gradually decreased from high tide to ebb tide. Sometimes H. o. osculans was observed to be taken from the surface of sand at high tide. In order to satisfy the energy demand required for H. o. osculans, it is considered foraging of bivalve is necessarly performed.
H. o. osculans population in Yubu Island clearly increased the foraging specialization using both tide line and nearby nest site to forage, but it is uncertain how it affects the long-term fitness of the population. I'm convinced continuous foraging study at the individual level can be quite useful for formulating an effective conservation strategy for H. o. osculans.
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