제주도에 서식하는 흑로 Egretta sacra의 번식생태와 관리방안

Abstract

제주도에서 흑로의 번식지 유지와 서식 환경을 보호하기 위해서는 여러 방해요인에 대한 대책과 관리방안을 수립해야 할 시점이다. 흑로의 개체군 보전을 위해서 서식지 및 종 수준에서는 여러 프로그램을 진행하여야 할 것이다. 첫째, 제주도 전역의 해안은 흑로의 취식지로 이용되는 곳이기 때문에, 해안조간대의 서식지가 손실되지 않도록 효율적인 관리방안이 필요하다. 둘째, 제주시 애월읍 신엄리의 번식지 일대의 동서 10㎞ 이내의 해안조간대 7곳은 흑로의 주요 취식지로 이용되고 있기 때문에 안정적으로 유지되도록 특별 관리되어져야 할 것이다. 셋째, 우도면 조일리, 애월읍 신엄리, 한경면 고산리, 남원읍 남원리 등의 해안절벽은 흑로의 주요 번식지로 이용되고 있으므로, 번식지 주변의 개발을 최소화하기 위한 행정적 제도 장치를 마련하여야 할 것이다. 번식지로 이용되는 해안절벽의 산책로는 절벽에서 내륙 쪽으로 5m 이상 이격되게 조정하고 번식기인 3～7월중에는 산책로 출입을 제한할 필요가 있다. 특히 애월읍 신엄리 일대의 해안절벽 150m 구간을 보호구역으로 지정할 필요가 있다. 넷째, 흑로의 종 보전을 위해서 제주도와 부속도서를 대상으로 번식하거나 월동하는 개체수를 모니터링 하여 개체군과 서식지 정보를 파악하여야 할 것이다. 다섯째, 흑로가 해안절벽이 발달된 곳에 국한하여 번식하기 때문에 종 자체를 천연기념물 또는 멸종위기 야생 동물로 지정할 필요가 있다. 여섯째, 흑로의 번식 성공률을 높이기 위해서는 번식지 주변의 인위적인 방해요인을 최소화하여 천적의 출현을 줄이고, 혹독한 기상조건을 극복할 수 있도록 번식지 관리가 필요하다.

This study was based on an investigation of the breeding sites, nidification habits, breeding ecology, breeding failure, and food of Pacific Reef Herons during breeding seasons from 2003 to 2005. 1. Breeding sites and nidification habits The nests were built on the ledges of cliffs in order to avoid predator attack. The found nests included a total of 31 places‥13 in Sineom-ri, Aewol-eup, 7 of Namwon-ri, Namwon-eup, 6 in Joil-ri, Udo-myeon, and 5 in Gosan-ri, Hangyeong-myeon. It turned out that the reuse rate of the nests was 61.5% in 2004, and 83% in 2005. The average reuse rate of nests was 72.0%. The mean height of the nest was 10.5±1.4 m above sea level. The selection of nest location was determined by the location and structure of the available ledges or grooves. The mean length of the nest was 77.8±3.1 ㎝, and the breadth was 56.2±3.8 ㎝. The nests of Pacific Reef Herons were larger than those of other egret species such as Black-crowned Night Herons, Cattle Egrets, Little Egrets, Great Egrets, the depth of the nests was relatively low. The nests were built up only with Peucedanum japonicum. 2. Clutch, egg size and breeding cycle The clutch size of Pacific Reef Herons was 3.24±0.2, and the eggs were laid at dawn or night at one to three-day intervals. The egg dimensions were: 46.73±0.31 ㎜ for length, 34.06±0.13 ㎜ for breadth, 27.67±0.50 g for weight, and 0.26±0.01 ㎜ in thickness. In regard to the breeding cycles of Pacific Reef Herons, nesting or nest repair was conducted from February to the end of April each year, egg laying from the beginning of March to the beginning of May, hatching from the beginning of April to the middle of May, and nest departure from the middle of May to the end of July. The supplement brood began from May to June when the first brood had failed. The incubation period was 28.17±1.7 days, and the fledgling period was 40.00±3.1 days. As compared with other egret species, the egg laying period of Pacific Reef Herons was earlier than that of the Black-crowned Night Herons, Little Egrets, and Great Egrets, but later than that of Grey Herons, in Korea. 3. The breeding success and breeding failure factors The hatching rate was 56.6%, the nest leaving rate of the hatched birds was 56.7%, and the breeding success rate was 32.1%. The breeding failure factors detected herein were as follows: eggs or chicks were eaten by predators (32.4%), the eggs or chicks fell out of their nests (29.7%), the incubation of eggs or the fledgling of chicks was abandoned (21.6%), and infertile eggs (16.2%). 4. The food resources and foraging sites The food resources of Pacific Reef Herons were identified as comprising 21 individuals of 5 species, and these identifications were verified as follows: 38.1% of Tridentoger obscurus, 19.0% of Ennedpterygius etheostomus, and 14.3% of Engraulis japonica. The sizes of the food resources were measured as follows: total 58.29±5.17 ㎜, T. obscurus was 67.49±4.91 ㎜, E. etheostomus was 43.98±3.50 ㎜, and E. japonica was 22.77±1.17 ㎜. The semi-digested foods were identified as Paralichthys olivaceus and Sebastes inermis. The primary foraging sites were 7.4 ㎞ (Oedocheon) east, to 6.6 ㎞ (Geumseongcheon) west of the Aewol breeding site. 5. Management for the conservation of Pacific Reef Herons We support a management plan targeted toward the prevention of the loss of the littoral zone of Jeju island for the foraging sites of Pacific Reef Herons. In particular, 7 sites in the littoral zones within 10㎞around the breeding site of Sineum-ri Aewoel-eup must be preserved and protected because they are the principal foraging sites of Pacific Reef Herons. An administrative system must be established to carve out a zone of protection from development around Jeju's cliff areas, including Joil-ri Udo-myeon, Sineom-ri Aewol-eup, Gosan-ri Hangyeong-myeon, and Namwon-ri Namwon-eup. A cliff walk should be located more than 5m from the cliffs that Pacific Reef Herons used as breeding sites, and walking should be prohibited near breeding sites in the season from March to July. In particular, the cliff around Sineum-ri, which is approximately 150 meters long, must be preserved. Monitoring must be carried out to evaluate the breeding and wintering population and habitat behavior of Pacific Reef Herons on Jeju island and its attached islets. The Pacific Reef Heron must also be designated as an endangered species or as a natural monument due to its limited breeding sites.