Nariko Oka

Nutritional Status of Dead Oiled Rhinoceros Auklets (Cerorhinca monocerata) in the Southern Japan Sea

Abstract We analysed the nutritional status of 44 oiled rhinoceros auklets (Cerorhinca monocerata) found dead along the Japan Sea coast. The species is a medium-sized Alcidae and one of the most vulnerable diving seabirds to oil spills in the northern North Pacific. We compared results with those obtained from 19 non-oiled auklets incidentally killed in fishing nets or predated at colonies as controls. All of the oiled birds were mal-nourished, having lost 60% of liver mass and 1/3rd each of their body, muscle and organ (e.g., uropygial gland) masses. They consumed 90% of their subcutaneous and abdominal fat and more than half of fats stored in muscles and other organs, thus having only 7 g total fat remaining. Bone marrow was almost entirely replaced with water. There were no stomach contents and livers were light, having lost nearly two thirds of mass. Low values for nutritional indices in the oiled group, compared with those of the non-oiled group, showed that oiled birds did not die instantly but died of nutritional exhaustion. A bird weighing 620 g on average was estimated to starve to death in one to two days after oiling, as oiled aquatic birds consume energy rapidly due to loss of thermoregulatory ability as a result of plumage oiling. As body mass is highly correlated both with organ mass and fat storage, as shown in detail in this study, body mass is effective as a simple and important index to evaluate nutritional recovery for use in determining the best time to return birds to sea after care in rehabilitation facilities. Based on our nutritional study, we recommend making every effort to rescue birds on the day they are oiled if rescue and rehabilitation are going to occur, as oiled birds quickly starve to death while at sea, especially during the cold winter.

Post-breeding movement and activities of two Streaked Shearwaters in the north-western Pacific

ABSTRACT We used miniature light-level/immersion loggers (geolocators) to study the movements and behavior of two Streaked Shearwaters (Calonectris leucomelas) during their travel away from Japan, after the breeding season. During the period from late October until late December, the tracked shearwaters moved south over subtropical pelagic waters with low productivity. The birds traveled to the seas off northern New Guinea and the Gulf of Carpentaria, Australia, 3400–5200 km distant from Mikura Island, their breeding colony in Japan. During the wintering period (December–February), the birds were on the sea surface for 77–85% of their time on average. The migratory and wintering behavior of Streaked Shearwaters are discussed in relation to the physical and biological marine environment of the north-western Pacific.

Individual consistency in migratory behaviour of a pelagic seabird

Many animals migrate between breeding and wintering areas; however, whether each animal behaves consistently in space and time between consecutive years is less well understood. Furthermore, previous breeding state (successful or failed) is often not considered when attempting to understand consistent individual differences in behaviour that are likely to impact upon the subsequent behaviour. Between 2006 and 2010, we used geolocators to track the migratory movements of a pelagic seabird, the streaked shearwater Calonectris leucomelas, with individuals (N=46) being followed for two years or more, including 23 birds that had chicks in two seasons and 23 birds in just one season. All individuals, except for one bird, migrated to the same broad wintering areas, and their migratory route as well as the centre of wintering distribution did not change in relation to the previous breeding outcomes. Migration schedules (dates of departure from the breeding colony, southward and northward migrations, and first return to the colony) did not differ significantly between years for individuals that had chicks during both years, while failed individuals left the breeding colony and appeared to start the southward migration at an earlier date than the previous successful year. Nonetheless, the timing of the southward migration was consistent within individuals, including both males and females, over successive years regardless of the previous breeding outcome, and also the timing of first return back to the colony for females that had chicks in the both previous years and eggs in the both following season. This may imply the existence of individual-specific broad time schedules, possibly a circannual rhythm, though ecological conditions might affect the exact timing of the actual departure event. Our results present evidence for high levels of individually consistent behaviour for this pelagic seabird outside the breeding season.

Foraging behavior and Diet of Streaked Shearwaters Calonectris leucomelas Rearing Chicks on Mikura Island

Abstract Foraging behavior and diet of Streaked Shearwaters Calonectris leucomelas rearing chicks on Mikura Island was studied using depth and temperature recording data-loggers and stomach contents. Water mass where birds were foraging was estimated using sea surface temperature experienced by birds. Birds spent 76–96% of their time at sea flying, 4–24% for landing on the water, and made a few (0.5–17.0 per day) shallow (<6 m) dives. Birds made many short (<2 days) and some long (4–10 days) trips. During short trips, birds stayed in the warmer Kuroshio and Kuroshio-Oyashio mixed regions, and fed on Japanese Anchovy Engraulis japonicus, Common Squid Todarodes pacificus and Flying Fish Cypselurus hiraii. During long trips, birds stayed in the colder Oyashio region and fed on anchovy and Pacific Saury Cololabis saira. Birds made more dives during short trips than they did during long trips. Streaked Shearwaters breeding on the island in low—productive Kuroshio water, therefore, adopted dual foraging strategies, and changed their diet and dive frequencies in relation to water masses.

Habitat selection by wintering tufted ducks with special reference to their digestive organ and to possible segregation between neighboring populations

Habitat selection by tufted ducks (Aythya fuligula), a diving duck which swallows benthic prey organisms, was studied during winter at two neighboring lagoons (Lakes Nakaumi and Shinji, Honshu, Japan) which differ strongly in their benthic fauna and in their diving duck densities. The ducks fed overwhelmingly on the dominant bivalve found in each of the two lagoons, the mussel Musculista senhousia in L. Nakaumi and the clam Corbicula japonica in L. Shinji. In general, however, the ducks probably preferred the mussels to the clams because of: (i) their high (2.9 times) calorific content for their weight; (ii) their high digestibility; (iii) their greater accessibility; and (iv) their shorter handling time. An average tufted duck (850 g) was estimated to require 1.3 kg of mussels or 3.8 kg of clams to meet their daily energy requirements. As a result, the two wintering populations were estimated to consume 4970 t mussels and 4770 t clams during a single wintering season, amounting to some 20% of the standing clam crop. Throughout the winter the average gizzard weight (37 g), and gizzard–body mass ratio (4.2%) of the Lake Nakaumi population were half those of the Lake Shinji population (73 g, 8.1%, respectively), despite their significantly similar nutritive body condition (% body lipid > 12%). The need to maintain a specialized gizzard mass in order to be able to cope with the different prey species results in little opportunity for ‘sampling’ movements of birds between lakes/prey types and as a result two subpopulations of ducks are indicated to be segregated.

Inter-colony differences in the incubation pattern of streaked shearwaters in relation to the local marine environment

Abstract. Foraging trip duration of breeding seabirds is affected by characteristics of available feeding habitat in the marine environment, which may, in turn, generate inter-colony difference in the patterns of nest attendance. Here, nest attendance patterns and foraging areas of Streaked Shearwaters (Calonectris leucomelas) during their incubation period were examined using global location sensors. The study was conducted at Sangan (SI) and Mikura Islands (MI) in the northwestern Pacific, and Awa Island (AI) in the Japan Sea during 2006–2009. The duration of incubation shifts showed significant inter-colony difference, but no sex-related difference. Shearwaters from SI had shorter mean incubation shifts (5.6 days on average; range 3.0-8.0 days) than those from MI (7.2 days; range 4.8–10.7 days) and AI (6.9 days; range 6.0–9.7 days). During the incubation period, SI and MI shearwaters foraged in the northwestern Pacifics Kuroshio-Oyashio transition area, while shearwaters from AI mostly foraged in the Japan Sea. The Northwestern Pacific represents a high-productivity zone, and SI shearwaters appeared to forage in these waters, where foraging efficiency is potentially high, leading to shorter incubation shifts. Also, although MI shearwaters foraged in the northwestern Pacific, the distance between their colony and foraging areas was greater (645 km on average; range 546–756 km), compared to SI (272 km; range 244–297 km) and AI birds (228 km; range 75–518 km). In this study, inter-colony differences in incubation shift length of Streaked Shearwaters appeared to be related to differences in foraging areas associated with the local marine environment.

Gender Identification by Calls and Body Size of the Streaked Shearwater Examined by CHD Genes

Abstract Like most seabirds Streaked Shearwaters Calonectris leucomelas have sexually monomorphic plumage. Researchers have conveniently identified gender in the field by means of two types of calls, associated with dimorphism in body size. By molecular sexing analysis using the chromo-helicase-DNA-binding (CHD) genes, we determined the gender of Streaked Shearwaters in relation to call types and body size. We recorded the type of calls, measured body dimensions and collected non-invasive samples (buccal cells or feathers) of Streaked Shearwaters at two breeding islands. As obvious amplification to identify gender by polymerase chain reaction (PCR) could not be obtained at high rates using a known universal primer pair, we developed two new primer pairs to identify gender in this species; this enabled us to identify the gender of all of the samples. Without exception all males gave high-pitched calls, whereas all females gave low-pitched calls. Molecular evidence also confirmed morphometric differences between males and females. We, therefore, conclude that Streaked Shearwaters exhibit sexual dimorphism in body size and call type. Males are significantly larger than females, and males give high calls whereas females give low calls.

Diet selectivity and shift of wintering common pochards and tufted ducks in a eutrophic coastal lagoon

Abstract Diet selectivity and shift of common pochards ( Aythya ferina ) and tufted ducks ( A. fuligula ) were investigated in the eutrophic coastal lagoon, Lake Nakaumi, during three winters (1994–1997). These two diving ducks fed mainly on mussels Musculista senhousia , but used food resources differently. Common pochards foraged larger mussels that were depleted earlier than the smaller ones eaten by tufted ducks. After the mussel biomass decreased in late winter, tufted ducks shifted their diet to clams Ruditapes philippinarum and Crustacea, while common pochards shifted only to the clam. Thus, depletion of mussel biomass in the lagoon affected common pochards earlier and stronger than tufted ducks. We suggest that different use of food resources of each species influenced their wintering patterns. Tufted ducks used the wintering area for a long period, while common pochards moved to the other area when animal foods became less abundant.

Basal and field metabolic rates of Streaked Shearwater during the chick-rearing period

Abstract The energetics of adult Streaked Shearwaters Calonectris leucomelas during the chick-rearing period were examined on Awa Island, Japan, in 2008 and 2009. Basal metabolic rates (BMR) were quantified using an open-flow respirometry system and field metabolic rates (FMR) were quantified using a doubly labelled water (DLW) method. In addition, we used activity loggers to estimate time allocations for different activities at sea. BMR was 0.0124 kJ g-1 h-1 (±0.0153, N=4) on average and corresponded to 54% of the value predicted from allometric equations. FMR was 0.0634 kJ g-1 h-1 (±0.0331, N=3) and was equivalent to 5.1 times BMR, which was higher than values reported for albatrosses (2–4 times BMR). Shearwaters made 50.3 landings a day (±9.8, N=12) and spent 44.8% (±8.0, N=12) of their time sitting on the water. They landed on water approximately twice as often as albatrosses (which have been well-studied using DLW), but they both spent similar proportions of their time on water. Frequent landings at sea, and frequent takeoffs, may generate incremental energetic expenses because of the use of flapping flight; therefore, the Streaked Shearwaters relatively high FMR may be related to its high number of landings.

Sexual Size Dimorphism in Streaked Shearwaters Calonectris leucomelas

Abstract We collected fresh Streaked Shearwater Calonectris leucomelas carcasses and describe sex differences in external measurements following sex identification using reproductive organs. Males had significantly deeper bills, longer bills, longer heads, longer tarsi, greater wingspans and greater wing areas than females, but overall wing and tail lengths and aspect ratios did not differ between sexes. Streaked Shearwaters showed a greater degree of sexual dimorphism in bill size than other Puffinus species. Comparing the wing loadings of male and female Streaked Shearwaters, the mass increase required for females to have the same wing loading as males is 0.036 kg. Females could feed to increase their body mass during a foraging trip to have similar wing loading to males.