Volume 2 Number 2 September 2003

Adaptations and maladaptations to island living in the Seychelles Warbler.

Animal Ecology Group, Zoological Laboratory, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands

The Seychelles Warbler (Acrocephalus sechellensis) was an endangered endemic of the Seychelles islands where, until 1988, the entire population of ca. 320 birds was restricted to the one island of Cousin Island (29 ha). Although warblers can breed independently in their first year, some individuals remain in their natal territory as subordinates, and often help by providing nourishment to non-descendent offspring. The frequency of helping is affected by habitat saturation, variation in territory quality (insect prey availability), and the genetic relatedness between the helper and the offspring. Helping results in indirect benefits from enhancing the reproductive success of close relatives, and direct benefits as improved parental skills and the acquisition of parentage. The overall helping benefits are higher for daughters than for sons, and it is therefore no wonder that most helpers are daughters from previous broods. Furthermore, on low-quality territories breeding pairs raising sons gain higher fitness benefits than by raising daughters, and vice versa on high-quality territories. Female breeders adaptively modify the sex of their single-egg clutches according to territory quality: male eggs on low quality and female eggs on high quality. However, despite the saturated nature of the Cousin population, the possibility of obtaining higher reproductive success on new nearby island, and a well developed flight apparatus, inter-island dispersal by Seychelles Warblers is extremely rare. The Seychelles Warbler is a beautiful example of behavioural and life history adaptations and maladaptations to restricted circumstances.

Johanna P. Pierre
Translocations in avian conservation: reintroduction biology of the South Island Saddleback (Philesturnus carunculatus carunculatus).
Marine Conservation Unit, Department of Conservation, P. O. Box 10-420, Wellington, New Zealand
Translocation is a commonly used tool in conservation management. However, because post-release monitoring has been infrequent in the past, reasons for the outcomes of translocations have often been unknown. Here, I review the reintroduction biology (including dispersal patterns, social organisation, survival, habitat use and foraging patterns) of a population of 26 South Island Saddlebacks (Philesturnus carunculatus carunculatus), on Motuara Island, New Zealand. After release on Motuara Island, South Island Saddlebacks dispersed widely through forest areas. During their first post-release breeding season, saddlebacks established territories of 1.9 ha-8.8 ha (mean 4.21 ha, SD 52.42) in size, and territorial confrontations were very rare. Saddlebacks bearing both adult and subadult plumage held territories and attempted to breed, and successful breeding produced approximately 10 fledglings. Saddlebacks foraged on a variety of plant species, dead wood and the ground. Except for five-finger (Pseudopanax arboreus), a preferred foraging substrate, birds foraged in all plant material in proportion to its availability. Saddlebacks preferred to forage in the lower levels of the forest. Although vegetation composition differed significantly between territories, all territories contained forest areas, and birds appeared to prefer foraging in larger sized trees. Large territory sizes, breeding attempts by young birds and rarity of territorial confrontations are most likely products of low population density. As density increases, birds are expected to occupy smaller territories, forage more efficiently within these smaller areas, start breeding at older ages, and possibly colonise scrub habitats. The translocated group sustained no more than 50% mortality at 8-10 months after release. In the past, translocations of 15-59 South Island Saddlebacks have been successful, suggesting that the relatively small founder group does not threaten the success of the transfer to Motuara Island. Saddlebacks are flexible in their habitat use, appear to readily adapt to ‘new’ environments and have high reproductive potential, increasing the likelihood of success of translocations of this species.

Mizuta T, Yamada H, Lin R-S, Yodogawa Y & Okanoya K
Sexing White-rumped Munias in Taiwan, using morphology, DNA and distance calls.
Laboratory of Ethology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
Methods of sexing the White-rumped Munia Lonchura striata phaethontoptila were investigated in eastern Taiwan. Twenty-six individuals were captured and their physical parameters were measured in the hand. Distance calls emitted when the birds were released were also recorded. The sex of each bird was confirmed using a DNA sexing method in the laboratory. Among the morphological traits measured, the tails and wings of males were significantly longer than those of females. An increasing stepwise discriminant analysis was performed to determine sex on the basis of morphological characters, however, only 84.0% of individuals were sexed correctly by such analysis. Distance calls of the White-rumped Munia were very similar to those of the Bengalese Finch, Lonchura striata var. domestica, the domesticated strain of the White-rumped Munia. Two distinct distance calls were recorded from birds on release, corresponding to the sexual difference confirmed by DNA testing. It is concluded, therefore, that the difference in distance calls is a useful trait that facilitates separation of the sexes in the field.

Matsubara H
Comparative study of territoriality and habitat use in syntopic Jungle Crow (Corvus macrorhynchos) and Carrion Crow (C. corone).
Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
Jungle Crows (Corvus macrorhynchos) and Carrion Crows (C. corone) are common species in Japan. They are closely related and considered 'ecological generalists'. I carried out a comparative study on territory and habitat use of these crows in an area where they occur syntopically. The two species defended their territories both intra- and interspecifically. The feeding behavior on the ground and the microhabitats in the territories differed between the species. Jungle Crow territories contained more urban areas, and they foraged mainly at garbage stations. In contrast, Carrion Crows mainly foraged in natural or at least un-paved microhabitats and stayed longer on the ground. Differences in microhabitat use and feeding behavior seemed to contribute to ecological separation between the two species of crows.

Hamao S
Reduction of cost of polygyny by nest predation in the Black-browed Reed Warbler.
Institute for Nature Study, National Science Museum, 5-21-5 Shiroganedai, Minato-ku, Tokyo 108-0071, Japan
When female birds choose already-mated males as their mates, they suffer some costs. One major cost is a reduction in male parental care. However, since nest predation disturbs the nesting cycles of polygynously mated females, it might change the allocation of male parental care between the females. I investigated the effect of nest predation on the relationship between female mating order and their brood status during the nestling-rearing period in the Black-browed Reed Warbler Acrocephalus bistrigiceps. Polygynous males did not feed later-hatched broods. The nest predation rate was high (56% of nests), which gives subsequently mated females a chance to receive male assistance. Four subsequently mated females acquired monogamous status by the time their eggs hatched, because the previously mated females had failed in their breeding attempts and disappeared from the territories. In addition, a subsequently mated female's nest was preyed upon and her renesting delayed her own nesting cycle, which resulted in the disappearance of the previously mated female with her fledglings and gave monogamous status at egg-hatching to the subsequently mated female. Furthermore, a case of inversion in the hatching order in polygynously mated females occurred by the prolonged pre-laying period of the previously mated female, which resulted in the subsequently mated female obtaining primary status at egg-hatching. As a result, 43% of the females that paired with already-mated males acquired monogamous or primary status at egg-hatching, whereas 69% of the females that paired with unpaired males did so. This suggests that nest predation reduces the cost of polygynous mating in this reed warbler population.

Kelvin S.-H. PEH & Fong Lin CHONG
Seed dispersal agents of two Ficus species in a disturbed tropical forest.
Department of Biological Sciences, National University of Singapore, Blk S2, 14 Science Drive 4, Singapore 117543, Republic of Singapore
Observations were carried out at the Bukit Timah Nature Reserve, Singapore on two species of the keystone genus, Ficus fistulosa and F. grossularoides. This study shows that the two species of different morphological characteristics (e.g. plant height, fruit colour and size) attracted different assemblage of avian frugivores. The frequency of visits by the avian frugivores was significantly different between the two Ficus species. The fig-eating frugivore communities feeding on both Ficus species seemed to be comparatively depauperate and a substantial number of members were the non-obligate (i.e. routine) avian frugivores. Mammalian frugivory was also observed. The mean number of feedings at F. grossularoides might not correlate with body size of the avian frugivores. Such information may aid the forest conservation and management of the nature reserve and future attempts at forest restoration.