Masaki Shirai

Applicability of the doubly labelled water method to the rhinoceros auklet, Cerorhinca monocerata

Summary The doubly labelled water (DLW) method is an isotope-based technique that is used to measure the metabolic rates of free-living animals. We validated the DLW method for measuring metabolic rates in five rhinoceros auklets (Cerorhinca monocerata) compared with simultaneous measurements using the respirometric method. We calculated the CO2 production rate of four auklets (mean initial body mass: 552 g±36 s.d.) injected with DLW, using the one- and two-pool models. The metabolic rate during the 24-h measurements in a respirometric chamber for resting auklets averaged 16.30±1.66 kJ h−1 (n = 4). The metabolic rates determined using the one- and two-pool models in the DLW method for the same period as the respirometric measurement averaged 16.61±2.13 kJ h−1 (n = 4) and 16.16±2.10 kJ h−1 (n = 4), respectively. The mean absolute percent error between the DLW and respirometric methods was 8.04% using the one-pool model and was slightly better than that with the two-pool model. The differences in value between the DLW and respirometric methods are probably due to oxygen isotope turnover, which eliminated only 10–14% of the initial enrichment excess.

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.

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.

Applicability of a Single-Sample Approach for the Doubly Labelled Water Method to the Streaked Shearwater Calonectris leucomelas

Abstract The doubly labelled water method is a common means of investigating field metabolic rates (FMRs) of free-ranging animals by injecting oxygen and hydrogen isotopes. Compared with a general two-sample approach including double blood sampling, a single-sample approach, which includes an estimation of initial isotope enrichment and single blood sampling, has been developed as a less invasive technique with lower impact on the behavior of study subjects. However, little attempt has been made to improve the indirect estimation of initial isotope enrichment and to apply the two-pool model for calculating FMR from the single-sample approach. Therefore, we studied the validity of a single-sample approach in the Streaked Shearwater Calonectris leucomelas. We developed equations for estimating initial isotope enrichment based on the amount of injected isotopes and body mass collected from 15 shearwaters. Then, for six shearwaters subjected to a two-sample approach, we calculated the turnover rates of oxygen and hydrogen isotopes (ko and kd), and FMR using the two-pool model with measured and initial isotope enrichments. The arithmetic errors were -0.01% for the estimated initial enrichments of oxygen isotope and -0.11% for hydrogen isotope. The ko, using estimated initial isotope, is overestimated by 3.2% on average, while kd is underestimated by 0.4% in comparison with those measured by the two-sample approach. The FMR measured by the single-sample approach are overestimated by 12.0% (± 12.1 SD) in comparison with those measured by the two-sample approach. We were able to estimate reliably the initial enrichments of both isotopes and apply the two-pool model in the calculation of FMR.

Laboratory evidence suggests glochidia metamorphosis in Sinanodonta japonica (Bivalvia: Unionidae) is supported by gills, but no other tissues of the host Gymnogobius urotaenia (Perciformes: Gobiidae)

ABSTRACT We quantitatively assessed the ability of the gills, caudal fin and scales of the floating goby Gymnogobius urotaenia (Hilgendorf, 1879) (Perciformes: Gobiidae) to serve as substrates for the larvae (glochidia) of the freshwater mussel Sinanodonta japonica (Clessin, 1874) (Unionida: Unionidae) by comparing parasitism success and metamorphosis success. We established three experimental treatments with 10 fish per treatment. Twenty glochidia were introduced onto one of the three body parts of each test fish by direct pipette infestation. Glochidia in the gill group had higher parasitism success than those in the fin and scale groups. Juvenile mussels were obtained only in the gill group. We quantitatively assessed the appropriateness of the three body parts as substrates for glochidia on the basis of three indicators: parasitism success; metamorphosis success; and parasitism and metamorphosis success. We conclude from our laboratory experiment that the artificial introduction of S. japonica glochidia onto G. urotaenia gills is a better procedure for obtaining juvenile mussels than the introduction onto fin or scales.

High levels of isotope elimination improve precision and allow individual‐based measurements of metabolic rates in animals using the doubly labeled water method

Doubly labeled water (DLW) can be used to measure energy expenditure in free‐ranging animals, but questions have been raised about its accuracy in different species or contexts. We investigated whether differences in the extent of isotope elimination affects the precision and accuracy of the DLW method, which can vary according to the experimental design or metabolic rate of the species. Estimated total energy expenditure by the DLW method (TEEdlw) was compared with actual total energy expenditure simultaneously measured via respirometry (TEEresp) in streaked shearwaters Calonectris leucomelas, a pelagic seabird. Subjects were divided into three groups with different experimental conditions: at rest on the ground for 24 h (Group A) or for 48 h (Group B), and at rest on the water for 24 h (Group C). TEEdlw in Group A matched TEEresp, whereas there was an overestimation of TEEdlw in both Groups B and C compared with TEEresp. However, compared with Group A, TEEdlw in Groups B and C had reduced the isotopic analytical variability and thus higher precision. The best regression model (TEEdlw = 1.37 TEEresp − 14.12) showed a high correlation (R2 = 0.82) between TEEdlw and TEEresp and allows a correction factor for field metabolic rates in streaked shearwaters. Our results demonstrate that the commonly made assumption that the DLW method is not appropriate for individual‐based estimates may be incorrect in certain circumstances. Although a correction factor may be necessary when using the DLW method to estimate metabolic rate, greater levels of isotope eliminations provides DLW estimates with high precision, which can adequately represent relative individual estimates. Nevertheless, the DLW method, should be used with caution when characterizing interspecies difference of energy expenditures.

Grazing Behavior and Local Management of Cattle and Buffaloes in Rural Laos

Laos presently is undergoing rapid economic development, which is also bringing about changes in the livelihoods of rural residents. While there is concern that these changes will also impact the way in which cattle and water buffalo are kept as livestock, there are few reports in the literature on the grazing behavior of these animals. In this chapter, we report on an ethological study on the spatiotemporal use of swidden fallow in northern Laos by primarily free-grazing cattle and water buffalo. In Kachet village, practicing swidden agriculture in northern Laos, livestock are grazed freely on first-year fallow following swidden agriculture. The results of an ethological survey utilizing global positioning system data loggers indicate that Kachet village offers environments that are suited to the free grazing of cattle and water buffalo. Shorter- and longer-term fallows in Kachet village serve different functions that are presumably necessary for the animals to maintain their body condition. We conclude that the grazing of livestock on swidden fallow constitutes rational use of space created by swidden agriculture. As this practice is well-suited to the villagers’ complex livelihood strategy, we must continue to evaluate the advantages of using swidden fallow for livestock grazing.