Various seabird foraging strategies during the non-breeding season have recently been revealed by combining the use of bio-logging devices and the study of stable isotopic signatures (δ15N and δ13C) from various tissues. In this study, we used these combined methods to determine the relationships between stable isotopic signatures in Black-tailed Gulls Larus crassirostris primary feathers and the areas in which the feathers are presumed to have been grown. The fifth primary (P5) feathers are replaced during late August, and although the migratory movements for seven of the eight gulls studied during this replacement period differed, the isotopic δ15N and δ13C values were similar. These values indicated that the seven gulls fed on a wide range of prey from krill to demersal fish species. The isotopic values from P5 for the individual gull that moved southward after breeding, were much higher than for the seven other birds. In contrast, all eight gulls showed a relatively narrow distribution during the replacement of their outermost primaries (P10), which were replaced during mid October and November. However, the isotopic values from P10 of the individual that moved southward during replacement of P5 were also much higher. The unique isotopic values of this gull might indicate specialization in anthropogenic food resources or high trophic level resources through the migration period, regardless of location. Contrary to previous studies, our research did not detect links between migratory movements and stable isotopic signatures from feathers in Larus gulls migrating through a relatively narrow range and having considerable individual variation in diet.
Antarctic Krill Euphausia superba is a key component of the Antarctic coastal marine ecosystem. Investigations into stable isotopic values of krill in predation hotspots are important in facilitating our understanding of the feeding environments of krill in a local coastal ecosystem. In this study we investigated stable isotopic values and maturity and size composition of krill at a small spatial scale, by logging GPS tracks of five Chinstrap Pygoscelis antarcticus and seven Gentoo P. papua penguins, and analyzing their stomach contents. The study was conducted at a penguin colony on Barton Peninsula, King George Island, Antarctica. The main food item of both species was Antarctic Krill (>98% wet mass). One Chinstrap and four Gentoo penguin foraging trips were classified as “on-shelf” trips, and four Chinstrap and three Gentoo Penguin foraging trips were classified as “off-shelf” trips. Krill collected from off-shelf trips had higher δ15N (4.22±0.28‰) values than those from on-shelf trips (3.78±0.29‰). The δ13C of the krill samples did not differ between the two penguin species or between trip types. The proportion of juvenile krill taken was higher for Chinstrap (13.04±4.97%) than Gentoo penguins (3.33±2.43%). Our results suggest that the main food source of the krill in our sample originated as non benthic planktonic/suspended organic matter, and that krill in off-shelf habitat may occasionally consume higher trophic level prey compared to those in on-shelf habitats.
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.
Large amounts of marine-derived nitrogen are carried ashore by seabirds in their feces (ornithogenic N). Various topological, meteorological, and environmental factors can affect microbial transformation of ornithogenic N altering the physical and biochemical conditions of the soils. Tsunami may be a factor affecting ornithgenic soil N dynamics leading to changes in soil conditions. We examined the effects of the tsunami triggered by the 11 March 2011 earthquake off the East Coast of Honshu, Japan, on ornithogenic soil N in the Black-tailed Gull Larus crassirostris breeding colony on Kabushima (Kabu Island) four months after the disaster. There were no differences in the total N content in soils between tsunami splashed (upper half of the island) and flooded areas (lower half), and the visual topography was comparable to that reported before the tsunami. It seems that the tsunami may not have extensively removed accumulated ornithogenic N in the soils, nor did it induce deposition of organic matter derived from marine sediments. However, δ15N values of soil N were lower in the area flooded by the tsunami than in the splashed area, suggesting the possibility that the tsunami caused leaching of ornithogenic N from the soil. Soils flooded by the tsunami contained higher levels of marine salts than those from the splashed area. N isotopic differences between NH4- and NO3-N were smaller in the flooded soils than in the splashed area. This indicates that nitrification of ornithogenic soil N is suppressed in the flooded area because of the remarkable increase in the salt concentration of the soil.
The water requirements of birds in humid areas are not well understood. Even rainforests have dry seasons, during which birds might experience water shortages. We surveyed use of puddles as a water source for birds in a New Caledonian rainforest during the dry season using camera traps. We found that birds frequently used puddles, and that especially granivorous and omnivorous birds were frequent water users. Almost all bird species visited puddles for bathing, but granivorous birds drank water significantly more often than other bird species. Our results suggest that even in tropical rainforests, birds depend on surface water.
The Oriental Skylark Alauda gulgula is a widespread species, but its natural history is poorly understood, especially at high altitudes. In this study, we collected breeding information on Oriental Skylarks at an altitude of 3,400 m on the northeastern part of the Tibetan Plateau and examined the effects of nest-site characteristics on nest success. The birds arrived in the study area in April, built nests in tufts of tall grass on the ground and laid their eggs (gray with brown speckles) between May and July. Clutch size averaged 3.3 eggs. Incubation was mainly by the female and lasted 12.4 days. The young left the nest when 9.7 days old. During the breeding season, individual skylarks made 2-3 breeding attempts. Nesting success, as measured by the proportion of nests from which at least one young fledged, was 41.3%. Predation accounted for the majority of failed nests. Some predators (e.g. carnivores) took both skylarks and Mountain Pikas Ochotona curzoniae, although the pikas, as the dominant mammals of the region were the key resource for their common predators. GLMM results show that the density of pika burrows around Oriental Skylark nests significantly influenced nesting success, while other potential variables were not statistically significant. Pika burrow density around successful nests was significantly lower than that around failed nests implying that an indirect effect of the presence of sympatric prey species with shared predators greatly influenced the nesting success of sympatric birds. Avoiding spatial interactions with coexisting key prey species of locally common predators is a successful strategy for improving nesting success.
A nest of the Ryukyu Scops Owl Otus elegans was found on Okinoshima (Okino Island), Fukuoka Prefecture, Japan (34.24°N, 130.10°E), in the Tsushima Strait, on 28 July 2013. The breeding pair and their three owlets were caught and their identity confirmed genetically using the BOLD System for COI in the mitochondrial genome. Their calls and external morphological measurements also accorded with what is known of the species. We estimated that at least 23 territorial males inhabit the Island. Okinoshima lies 490 km beyond the previously known northern limit of the species' distribution.