Examinando por Autor "Zavalaga, C.B."

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  • Miniatura
    ÍtemAcceso Abierto
    Sex-related differences in the foraging movement of streaked shearwaters calonectris leucomelas breeding on Awashima Island in the sea of Japan
    (Ornithological Society of Japan, 2017) Matsumoto, S.; Yamamoto, T.; Yamamoto, M.; Zavalaga, C.B.; Yoda, K.
    Sex-related differences in foraging habitat are common among seabirds. Streaked Shearwaters Calonectris leucomelas breeding on Awashima Island in the Sea of Japan are considered to exhibit gender differences in foraging habitat: only males cross the windy Tsugaru Strait into the Pacific Ocean. Since males are larger, with greater wing loading than females, winds are expected to increase the effect of sexual size dimorphism on their flight performance, which may determine accessibility to foraging habitats. To assess the sex-related differences in foraging movements among years in which environmental and wind conditions differed, we analyzed foraging trips of male (N=243) and female (N=241) Streaked Shearwaters during the chick-rearing period by using GPS loggers in 2011, 2012, and 2013. Both males and females were found to travel through the Tsugaru Strait into the Pacific Ocean, but the frequency was higher for males than for females. Nevertheless, we found that wind velocities had no effect on the probability of transiting the Tsugaru Strait. Greater wing loading requires higher energy demands for flight; therefore, males possibly needed to travel into the Pacific Ocean to feed on the energy-rich Pacific Saury Cololabis saira. In 2012, when the sea surface temperature (SST) in the Sea of Japan was the highest among the three study years, the frequency of foraging in the Pacific Ocean was similar for males and females. Shearwaters are considered to forage in association with predatory fish, the distribution of which is largely influenced by the Tsushima Warm Current migrating partially into the Tsugaru Strait. Hence, both males and females were more likely to travel into the Pacific Ocean when the Sea of Japan SST was high, generating conditional sex-related differences in foraging habitat. © The Ornithological Society of Japan 2017.
  • Miniatura
    ÍtemAcceso Abierto
    Unveiling an important Humboldt penguin (Spheniscus humboldti) breeding colony in Perú and the need for its protection against the potential impact of guano harvest
    (The Waterbird Society, 2015) Zavalaga, C.B.; Alfaro-Shigueto, J.
    Humboldt Penguins (Spheniscus humboldti) are globally Vulnerable due to the decline of the population and to a decline in the number of breeding sites in comparison to historical records. In 2010, we observed a few thousand Humboldt Penguins nesting in a surface-nest colony on Isla Santa Rosa in southern Perú. This number was unexpected because this site has never been listed as an important Humboldt Penguin breeding ground. We visited this island again in June 2011 and 2012, and counted 1,965 and 1,745 active nests, respectively. These numbers indicate not only the presence of at least 3,500-4,000 Humboldt Penguins, but places Isla Santa Rosa among the five largest Humboldt Penguin colonies within its entire range. The need for recognition of Isla Santa Rosa as a major Humboldt Penguin refuge is crucial for the conservation of the species, as the island has remained untouched from guano harvesting since 1996. This has resulted in a significant accumulation of guano likely to be legally collected in the next few years. Unsupervised guano harvesting could cause a Humboldt Penguin exodus and jeopardize the existence of this colony. Under this scenario, it is recommended that Isla Santa Rosa be closed to guano harvesting until a surveillance program to protect the Humboldt Penguins can be established and proven to work under the conditions found on Isla Santa Rosa. © 2015, The Waterbird Society. All rights reserved.