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Publications (11)3.91 Total impact

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    ABSTRACT: 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 CO(2) 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.
    Biology open. 11/2012; 1(11):1141-5.
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    ABSTRACT: In some bird species, the survival of chicks hatching later in the season is lower than those hatched earlier due to increased risk of predation and a seasonal decline in feeding conditions. To reduce these risks, it might be advantageous for late-hatched chicks to grow faster and hence fledge at younger age. In this experimental study, the growth rates of early- and late-hatched Rhinoceros Auklet Cerorhinca monocerata chicks were compared under average and poor food supplies in captivity. Controlling for potentially confounding effects of chick mass at 10 days old, chick age and nest-chamber temperature, late-hatched chicks had higher wing growth rate than early-hatched chicks before attaining the minimum wing length required for fledgling under both average and poor food supplies. After attaining the minimum wing length, however, late-hatched chicks had a lower fledging mass, indicating a potential cost that could diminish the early advantage of fast wing growth.
    Ibis 01/2012; 154(2):296-306. · 2.36 Impact Factor
  • Japanese Journal of Ornithology 01/2010; 59(1):38-54.
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    ABSTRACT: We studied the foraging behaviour of adult thick-billed murres Uria lomvia as they reared their chicks at St. George Island, Alaska, USA, relative to the thermal structure of the nearby ocean water column in the summers 2004, 2006, and 2007 using data recorders attached to the birds. The thermal structure of the upper ocean varied substantially among the years. Satellite-derived sea surface temperature (SST) and water temperature at depths >40 m were higher in 2004 than in 2006 and 2007 (9.1, 8.3 and 7.8°C for mean SST; 5.1, 4.4, and 2.2°C for median bottom temperature, respec- tively). We recorded a strong thermocline in 2004 and 2007, but not in 2006. Nonetheless, the thermo- cline was one of the important foraging habitats in all years. The foraging behaviour of thick-billed murres appeared to vary with annual variation in the intensity of the thermocline and water temper- ature at depth and evidently with associated vertical distribution of prey. Birds spent more time forag- ing in stratified waters and dived to around thermocline depth (and deeper in 2007) in 2004 and 2007. However, the birds used both stratified and mixed waters in 2006 and were less likely to dive to ther- mocline depth. Main prey items delivered to chicks varied among years. Sandlance (53% of observed items) and pollock (23%) predominated in 2004, compared with cephalopods (23%), flatfishes (17%) and pollock (15%) in 2006, and cephalopods (62%), pollock (16%) and sculpins (9%) in 2007.
    Aquatic Biology - AQUAT BIOL. 01/2010; 8:289-298.
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    ABSTRACT: Sea-surface temperature (SST) directly and indirectly affects the distribution and abundance of prey species for seabirds, so we expect variation in SST to be associated with variation in seabird life history traits. In black-tailed gulls (Larus crassirostris) at Teuri Island in northern Hokkaido, Japan, we investigated the diet of the gulls prior to egg laying in 2004 and 2005, and examined the influences of SST in March or April, when the gulls congregate in the colony, on egg-laying parameters using 13years of data (1992–2004). The gulls fed on krill (Thysanoessa inermis) and fish prior to the egg laying. Mean first egg dates and clutch sizes were significantly and quadratically related to SST anomalies in March, but were not influenced by SST anomalies in April. There was no significant effect of SSTs in either March or April on egg volume. Sea-surface temperature anomalies in March of the years of early laying (−1 to 1°C) were higher than those in 2001 (−2.2°C), but lower than those in 1992 (+1.2°C) and 2004 (+1.1°C). Thysanoessa inermis congregates to spawn at the sea surface, when SSTs rise 3−4°C. Thus, a mismatch between food availability and the timing of egg production in the gulls could have occurred in these 3years. This study suggests that SST fluctuations prior to laying are important in breeding success of black-tailed gulls.
    Ecological Research 01/2009; 24(1):157-162. · 1.55 Impact Factor
  • Yuzan Tanaka, Motohiro Ito, Yutaka Watanuki
    Japanese Journal of Ornithology 01/2009; 58(1):46-54.
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    ABSTRACT: Predator-prey relationships are key to understanding complex marine ecosystem dynamics. The match-mismatch hypothesis posits that predators time energy-intensive activities, such as reproduction, to periods of high food availability. However, predators may be constrained by various ecological or physiological processes, leading to mistimed activities relative to prey availability. We investigated inter-annual variation in the timing of breeding for a piscivorous seabird (rhinoceros auklet Cerorhinca monocerata) in relation to availability of a preferred prey item, Japanese anchovy Engraulis japonicus, using data collected over 18 yr between 1984 and 2006 at Teuri Island in the northern Japan Sea. Our primary goals were (1) to identify the climatic factors that affect the seabirds' timing of breeding, proxied by hatching date, and anchovy seasonal availability, and (2) to quantify the fitness effects of predator-prey matches and mismatches relative to climate variability. Hatching date was later in years with lower spring air temperatures. Auklets switched their feeding from sandlance and juvenile greenling to anchovy when it was transported into the birds' foraging range with the seasonal northern expansion of 13 degrees C warm water from the south. The mismatch between hatching date and the period of high anchovy availability was most pronounced when spring air temperatures were warm, and there was a weak Tsushima (warm) Current. Spring air temperature was influenced by spring atmospheric pressure gradients in the Arctic and northern Eurasia, which drive the east Asian winter monsoon, whereas timing of the Tsushima warm water expansion was influenced by winter surface pressures over the western North Pacific. Chick growth rates, mass at fledging, and overall fledging success (fitness) were lower during mismatch years when the auklets fed less on anchovy. The auklets were constrained to adjust hatching date because the seasonal mismatch appeared to be driven by independent and unpredictable surface pressure patterns.
    01/2009;
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    ABSTRACT: The structure of a marine food web can change quickly within seasons as well as interannually in response to physical oceanographic changes. In this study, we examined the relationship between temporal changes in the marine ecosystem of northern Hokkaido, Japan, and diets of rhinoceros auklets Cerorhinca monocerata breeding in this region. To obtain an integrated measure of changes in diet composition on short (days) and inter-annual (2004 and 2005) time scales, we used a 2-pronged approach. We examined (1) the diets of adults using stomach contents and stable isotope signatures in tissues, and (2) chick diets using the composition of bill-loads delivered to chicks. During the incubation period, the diet of adults comprised euphausiids (Thysanoessa longipes and T inermis). During the chick-rearing period, the diet of adults was age 0 Japanese sandlance Ammodytes personatus and age 0 Japan Sea greenling Pleurogrammus azonus in the early period, but switched quickly (<10 d) to warm-water-preferring Japanese anchovy Engraulis japonicus when the warm Tsushima Current intruded into their foraging range. Adult blood plasma stable isotope ratios reflected these seasonal changes in stomach content. Diets did not differ between age categories. Furthermore, the timing of diet switching to anchovy differed inter-annually, and was about 10 d later in 2005 than 2004, reflecting a difference in the timing of the intrusion of warm water. We conclude that rhinoceros auklets respond sensitively to current-related rapid marine food web changes.
    01/2009;
  • Motohiro Ito, Yutaka Watanuki
    Japanese Journal of Ornithology 01/2008; 57(2):140-147.
  • Japanese Journal of Ornithology 01/2008; 57(2):148-153.
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    ABSTRACT: International Symposium, "The Origin and Evolution of Natural Diversity". 1–5 October 2007. Sapporo, Japan. Availability of fish as the prey of seabirds undergoes extreme changes under temporal and spatial variations of marine environments. Successive monitoring of prey species and breeding performance of seabirds at different colonies may clarify a part of the effects of these variations of marine environments. Prey species and growth rates of chicks of Black-tailed Gull Larus crassitostris at Teuri and Rishiri Island, Hokkaido, Japan, were measured from 1998 to 2006, and the effects of sea surface temperature (SST) were analyzed. At both islands, 0 + and > 1 + Japanese sand lance Ammodytes personatus and Japanese anchovy Engraulis japonica were main prey of chicks. At Teuri Island, chicks grew rapidly in the year when SST anomalies in June was low, except for 2006 when SST in June was extremely low, although prey species composition did not affect growth rates. At Rishiri, in the year when SST anomalies in July was high, the mass proportion of anchovy was small but that of 0 + sand lance was greater, and chicks grew rapidly, except for 2006 when SST in July was extremely high. The results suggest an increase in availability of (i) all prey species when SST in June is high or low outside of optimum range at Teuri, and of (ii) 0 + sand lance during high SST in July at Rishiri. Although the two islands are just 90 km apart, prey species determining chick growth of Black-tailed Gull and the marine environmental factors that enhance the prey availability seem to be significantly different in them.
    01/2008;