Jeong-Chil Yoo

The Palearctic Oystercatcher Haematopus ostralegus, a Natural Definitive Host for Gymnophalloides seoi

In order to verify the role of migrating birds as natural definitive hosts for Gymnophalloides seoi (Gymnophallidae), Palearctic oystercatchers, Haematopus ostralegus, were caught from several western coastal areas in the Republic of Korea and examined for intestinal flukes. Five (71.4%) of 7 oystercatchers were infected with 302–1,660 (mean 892) adult G. seoi. In intestinal sections of the host, worms were found in the intervillous space of the mucosal layer. We conclude that the oystercatcher is a natural definitive host for G. seoi.

Egg survival is related to the colour matching of eggs to nest background in Black-tailed Gulls

A long-standing hypothesis posits that, for species with exposed nests, a close match between the colour of the eggs and that of the nest in which they are laid should enhance egg survival, but this has rarely been tested in a rigorous manner. Here, we demonstrate the effects of egg–nest colour matching on egg survival in Black-tailed Gulls (Larus crassirostris) on Hongdo Island, Korea. We quantified the ground colour of eggshells and that of the nest background using a digital camera and computerized RGB and greyscale colour systems. We show that a close match of eggshell ground colour and nest background colour was associated with increased chances of eggs surviving through to hatching. In particular, there were strong survival advantages for eggs matching the nest colour in sites with poor concealment, whereas there was no effect of eggshell ground colour in nests that were more concealed by vegetation. Our findings support the hypothesis that egg colour functions to make eggs cryptic and that egg colouration may be a significant factor affecting egg loss.

Effect of host egg color dimorphism on interactions between the vinous‐throated parrotbill (Paradoxornis webbianus) and common cuckoo (Cuculus canorus)

To investigate the effect of host egg color dimorphism on the vinous‐throated parrotbill (Paradoxornis webbianus) – common cuckoo (Cuculus canorus) interactions, we monitored breeding nests of vinous‐throated parrotbills, and conducted model egg experiments, using two colors: white and blue. Of the 190 nests examined in this study, cuckoo parasitism occurred at 10 nests (8 blue and 2 white egg clutches, respectively), and only blue cuckoo eggs were found. This frequency was similar to the egg‐color ratio of all host nests found (151 blue and 39 white egg clutches). Vinous‐throated parrotbills showed high rejection rate towards both cuckoo eggs and model ones. There was a significant difference in rejection rates towards mimetic (blue) and non‐mimetic (white) eggs in blue egg clutches. Mimetic eggs put in nests took significantly longer to be rejected than non‐mimetic ones. The most common rejection method used by the hosts was egg ejection (puncture‐ejection). The costs of ejecting non‐mimetic eggs tended to be lower than those of ejecting mimetic eggs. These results indicate that egg‐color dimorphism in this species favors the individuals having white egg clutches in terms of higher rejection rate and lower ejection costs of the parasitic eggs. This study also suggests that egg‐color dimorphism of the vinous‐throated parrotbill decreases the effect of cuckoo parasitism on host populations.

“cu-coo”: Can You Recognize My Stepparents? – A Study of Host-Specific Male Call Divergence in the Common Cuckoo

The presence of multiple host-specific races in the common cuckoo Cuculus canorus has long been recognized as an evolutionary enigma but how this genetic divergence could be maintained is still equivocal. Some recent studies supported biparental genetic contribution in maintaining the host-races, implying the necessity that they should recognize and mate assortatively with those who belong to the same host-race. One potential mechanism to accomplish this is that males may produce distinctive calls according to host-specific lineages. In order to test this hypothesis, we carried out a comparative study for male cuckoo calls recorded from three distant populations, where two populations share a same host species while the other parasitizes a different host species. Populations with similar habitat structures, maintaining comparable distance interval (ca. 150 km) between neighboring ones, were selected so as to minimize any other causes of vocal differentiation except the pattern of host use. By comparing the vocal characteristics of male cuckoos at the level of individual as well as population, we found that individual males indeed produced different calls in terms of spectral and temporal features. However, these differences disappeared when we compared the calls at the population level according to host species and geographic location. In conclusion, it seems unlikely for the cuckoos to identify the stepparent of male cuckoos based solely on the vocal characteristics, although they may be able to use this cue for individual recognition. Future studies including detailed morphological and genetic comparisons will be worthwhile to further elucidate this issue.

Egg Rejection by Both Male and Female Vinous-throated Parrotbills Paradoxornis webbianus

Abstract In bird species that suffer brood parasitism, the question about which sex is responsible for egg rejection has important implications for determining the coevolutionary relationship between brood parasites and their hosts. In order to determine which sex rejects a parasitic egg in vinous‐throated parrotbills (Paradoxornis webbianus) which have egg color dimorphism, we conducted model egg experiments and video‐recorded the behavior of the focal pair. Both sexes showed rejection behavior to the parasitic eggs. It indicates that the vinous‐throated parrotbill may have a high rejection rate and faster spread of any rejection alleles through out populations. However, further studies are still needed to confirm the egg recognition mechanism in this species, which will expand our knowledge of the evolutionary relationship between host and parasite.

Distribution of Waterbirds in Rice Fields and Their Use of Foraging Habitats

Abstract. Over the course of a year, rice fields display spatial and temporal differences according to farming management practices, providing a succession of habitats throughout the crop-growing cycle for various waterbird species. However, few studies have assessed the influence of the spatial and temporal differences produced by rice field farming management practices on waterbird species during a year. The present study investigated spatial and temporal patterns of species distribution and examined the factors that affect waterbird selection of foraging habitats in the rice fields located in the midwestern part of South Korea from April 2009 to March 2010 and from April 2011 to March 2012. Waterbird species represented strong seasonality and selectively used different field types at a fine spatial scale. The selection of field type depended more on field structures that were related to the vulnerability of prey items than on prey abundance in rice fields. Water level was an important factor that affected shorebird selection of foraging habitat, and they chose habitats with different water levels according to their body size. The density of rice plants was a critical factor affecting the selection of habitats by herons, because densely planted fields inhibited their access to food. The presence of rolled straw in rice fields affected the distribution of waterfowl. These results demonstrate that farming management practices, which determine prey accessibility, strongly affect the use of rice field habitats by waterbirds. Our knowledge of these relationships should be incorporated into conservation practices protecting the various waterbird species that use rice fields.

A Study of Feeding Methods in Five Species of Herons and Egrets in Korea

Feeding methods of five species of herons and egrets were studied in an agricultural landscape in Asan city, Chungcheongnam-do, Korea in 2006. Grey herons primarily hunted while standing, whereas great egrets fed while walking slowly. Two smaller species, little and cattle egrets, were active foragers, feeding both while walking quickly and walking slowly. Little egrets were the only species using the foot stirring method. The medium-sized heron, intermediate egrets, foraged mainly while walking slowly or leaning. For grey herons, great egrets and little egrets, the frequency of use of different feeding methods was different between habitats: these species used the leaning method more frequently in rice fields than in reservoirs and ditches. Also, most herons (all species other than great egrets) showed seasonal changes in their feeding methods that are related to changes in habitat condition.

Foraging Habitat Preferences of Herons and Egrets

We investigated the foraging habitat preferences of herons and egrets in an agricultural area in Asan city, Chungcheongnam-do, Korea. In the study area, rice fields were the most abundant habitat type (86.8%) and total suitable feeding habitat was greater in the northern area (59.0%) than the southern area (22.5%) of the colony. Most feeding herons and egrets were located in the northern area of the colony. The number of feeding individuals in a given area was related to the available feeding area (Pearson correlation, r=0.773, p< 0.001 for field habitats; r=0.901, p< 0.001 for freshwater habitats). Feeding habitat preferences differed among species. Grey herons ( Ardea cinerea ), great egrets ( Egretta alba ), and black-crowned night herons ( Nycticorax nycticorax ) used reservoirs and ditches. However, intermediate egrets ( E. intermedia ) and cattle egrets ( Bubulcus ibis ) were dependent on rice fields. The little egret ( E. garzetta ) was a habitat generalist using all types of habitats. The two largest species, grey herons and great egrets, fed at deeper site than little egrets and foraged in deeper sites in reservoirs than in ditches ( χ 2 -test, χ 2 3=26.6 and p< 0.001 for grey herons, χ 2 3 =17.5 and p< 0.001 for great egrets). All species displayed seasonal changes in feeding habitat use and these changes were related with changes in availability of feeding habitats.

Spatial patterns, ecological niches, and interspecific competition of avian brood parasites: inferring from a case study of Korea

Since obligate avian brood parasites depend completely on the effort of other host species for rearing their progeny, the availability of hosts will be a critical resource for their life history. Circumstantial evidence suggests that intense competition for host species may exist not only within but also between species. So far, however, few studies have demonstrated whether the interspecific competition really occurs in the system of avian brood parasitism and how the nature of brood parasitism is related to their niche evolution. Using the occurrence data of five avian brood parasites from two sources of nationwide bird surveys in South Korea and publically available environmental/climatic data, we identified their distribution patterns and ecological niches, and applied species distribution modeling to infer the effect of interspecific competition on their spatial distribution. We found that the distribution patterns of five avian brood parasites could be characterized by altitude and climatic conditions, but overall their spatial ranges and ecological niches extensively overlapped with each other. We also found that the predicted distribution areas of each species were generally comparable to the realized distribution areas, and the numbers of individuals in areas where multiple species were predicted to coexist showed positive relationships among species. In conclusion, despite following different coevolutionary trajectories to adapt to their respect host species, five species of avian brood parasites breeding in South Korea occupied broadly similar ecological niches, implying that they tend to conserve ancestral preferences for ecological conditions. Furthermore, our results indicated that contrary to expectation interspecific competition for host availability between avian brood parasites seemed to be trivial, and thus, play little role in shaping their spatial distributions and ecological niches. Future studies, including the complete ranges of avian brood parasites and ecological niches of host species, will be worthwhile to further elucidate these issues.

Evaluation of environmental factors to predict breeding success of Black-tailed Gulls

Abstract This study demonstrated prediction of breeding success of Black-tailed Gulls in relation to the selected environmental factors through evaluation of relative importance in determining breeding success. The data were obtained from the 258 selected and 120 non-selected sites for breeding of the gulls during the breeding periods in 2002–2003. Breeding success at the selected sites, and environmental factors such as vegetation cover, vegetation height, rock cover, nest-wall, nearest distance between neighbors and slope, were measured at each sampling site. For predicting breeding success of Black-tailed Gulls, we used two different artificial neural networks in this study: self-organizing map (SOM) and multilayer perceptron (MLP). SOM was used to classify the sampling sites based on the environmental factors, whereas MLP was implemented to prediction of breeding success of the gulls at the non-selected sites based on environmental conditions. In our results, SOM discriminated clearly the sampling sites and presented differences in environmental factors between the selected and non-selected sites. Subsequently, the breeding success was accordingly predicted by MLP. Nest-wall was considered the most important environmental factor in determining survival status of the gulls. An increase in nest-wall and vegetation cover was required to support breeding of the specimens for managing the habitats for Black-tailed Gulls.