The amount of energy that organisms can allocate to self-maintenance and/or reproduction largely depends on their foraging strategies. Because of corticosterone (CORT) involvement in the control of energy metabolism, food intake and locomotor activity, recent studies have sought to demonstrate the role of this hormone in foraging decisions and performance. Moreover, considerable recent advances in animal-attached loggers now allow the study of behaviour in free-living animals. In order to assess the effects of CORT administration on the foraging behaviour of free-living Adélie Penguins Pygoscelis adeliae, we studied a group with CORT implants and a control group without CORT implants, by attaching time-depth recorders to the two groups and monitoring them throughout up to seven consecutive foraging trips during the guard stage (in Adélie Land, Antarctica). We found that foraging trips duration was similar between both groups. Dive durations, time spent at the bottom phase of dives, and the number of undulations per dive of CORT-implanted birds were all significantly higher than those of controls. However, CORT-implanted birds performed fewer dives overall (ca. 4,400) than controls (ca. 6,250) and spent many (13 and 6 times for penguins #3 and #4, respectively) long periods (>3 h) without diving. The low foraging effort and long resting periods support the view that CORT-implanted birds probably gained less energy than did the control birds. CORT treatment appears then to result in redirecting bird behaviour from costly activity (i.e. reproduction) to a behaviour promoting the preservation of energy reserves. Future studies are therefore needed to assess body condition and reproductive success of CORT-manipulated birds in parallel with the recording of their diving performances.
Testosterone affects male sexual-, aggressive-, and parental-behaviors in bird species. To understand the breadth of the proximate contribution of testosterone to breeding behaviors in male Black-tailed Gulls Larus crassirostris, sexual behaviors, aggressive behaviors against egg-predators and conspecifics, and chick-provisioning behavior of five testosterone-implanted males (T-males) were observed and compared with those of three control males (placebo-implanted; C-males). T-males showed significantly higher levels of courtship and copulation behaviors than C-males. The levels of aggressiveness against egg-predators and against conspecifics, and the rate of feeding of chicks did not differ between T- and C-males. These results suggest that sexual and mating behaviors in male Black-tailed Gulls may be affected by testosterone, while aggressive- and feeding-behaviors are affected by certain ecological factors, such as individual age, or a necessity for high levels of feeding by males, rather than by testosterone.
Mother birds can enhance growth and/or survival of chicks by supplying energetic and hormonal resources to the egg yolk (i.e. maternal effect). In several bird species, mothers supply higher level of testosterone to the eggs laid later within the clutch and enhance the growth of the chick to compensate for the disadvantage of the later hatching. As same as this within-clutch mechanism, mothers breeding later in the season can be expected to supply higher level of testosterone to the clutch. However, among-clutch seasonal variation in yolk testosterone levels has been rarely described. Here, we investigated among-clutch seasonal variation in the yolk testosterone level in Black-tailed Gulls Larus crassirostris, as well as within-clutch variation. Mean yolk testosterone level of eggs laid later within the clutch (“b-eggs”) was significantly higher than that of eggs laid earlier (“a-eggs”). The yolk testosterone levels of both a- and b-eggs of later breeders were significantly higher than those of earlier ones, while this trend was not observed in mean egg mass. Our results indicate that mothers establishing the clutch later in the season would invest more maternal testosterone into the clutch.
Alcids dive longer than are predicted by their body size alone, but the physiological mechanisms that explain their excellent diving capabilities are poorly understood. In this study, we estimated the oxygen stores of Rhinoceros Auklets Cerorhinca monocerata, medium-sized alcids that attained depths down to 62 m within 2.5 min. Hematocrit was 43.9±2.8%, hemoglobin concentration was 17.2±4.6 g·100 ml-1, and blood volume was 12.7±1.9% of their body mass. Myoglobin concentration in breast muscle (1.8±0.3 g·100 g-1) was higher than that in leg muscle (1.2±0.2 g·100 g-1). Rhinoceros Auklets have higher blood volume, hemoglobin and myoglobin concentrations, as do other flying/diving seabirds (other alcids and cormorants), than flying/non-diving seabirds (terns and kittiwakes). The oxygen store of Rhinoceros Auklets was estimated at 54.5 ml·kg-1. Using the average oxygen consumption rate of diving seabirds (1.01 ml·s-1·kg-1), we calculated their theoretical aerobic dive limit (TADL) as 53.9 s. Nearly half of their dives (47.2%) exceeded their TADL, because an overestimation of their oxygen consumption rate during diving resulted in an underestimation of TADL.
Measuring the individual body conditions of living birds is essential for understanding tradeoffs in life-history studies, especially in long-lived species. The aim of this study was to further develop a method for measuring body condition (lipid content), without killing birds. In theory, the lipid content mass in the body should have a close inverse relationship with water mass. Using this relationship, body condition can be evaluated without killing because the amount of water in the body can be estimated in live birds. However, the inverse relationship has only been shown to exist in a few studies of bird species. In this study, significant inverse relationships between water and lipid contents of three seabird species, Leach's Storm-Petrel Oceanodroma leucorhoa, Rhinoceros Auklet Cerorhinca monocerata and Black-tailed Gull Larus crassirostris, were shown. These facts highlight that body condition (lipid content) , can be estimated from the water content of the body.
Procellariiform seabirds accumulate large amounts of lipid during the nestling period. Chick obesity functions as a buffer against irregular attentiveness by parents delivering meals. Surprisingly the assimilation mechanism necessary to attain obesity remains unclear. This study presents the first measurements of assimilation efficiency in relation to age and diet throughout the long nestling period of a Procellariidae. To determine the assimilation efficiency and diet effects on growth, Short-tailed Shearwater Puffinus tenuirostris chicks were fed in captivity on different diets of marine organisms (krill Euphausia superba, squid Nototodarus sloani and fish Hyperlophus vittatus) from age 10 to 85 days. Assimilation efficiency was highest (mean 93.7%) among young chicks (10-29 days old) then declined, becoming stable (mean 80.9%) among older (70-85 days old) pre-fledging chicks. It was noted that the krill-fed chicks showed consistently higher assimilation efficiencies, not only when young (mean 95.4%) but also when older (mean 84.8%), than the squid-fed or fish-fed chicks (means 92.4-93.3% when young and 78.4-79.5% when older). The krill diet contributed to better growth in body mass (close to that of free-living chicks at the source colony), while the squid- and fish-fed chicks grew slowly. The dietary effects on feather growth and molting did not parallel those on body mass increments. Squid-fed chicks had similar feather growth rates and molt progress to those of krill-fed chicks, whereas fish-fed chicks often vomited their food when given sizable quantities of fish and had slower feather development and molting. These findings suggest that chicks may need parental digestive fluids in order to facilitate their digestion of larger amounts of fish, whereas they were competent to digest krill and squid on their own. When the diet of older (over 85 days of age) fish-fed chicks was changed to krill they stopped regurgitating food, gained weight and began rapid molting. Likewise, squid-fed chicks gained mass at a faster rate when they were switched to a diet of krill. The experimental Short-tailed Shearwater chicks were found to have a high absorption capability during the early nestling stage allowing for considerable lipid accumulation and resulting in obesity. This obesity facilitates the fasting necessary while their parents commute to distant nutritive waters. The shearwaters have a highly adaptive potential to assimilate krill, which are abundant organisms with a large biomass in the higher latitudes that shearwaters prefer to inhabit for foraging throughout the year. Even the krill-fed chicks, the best among the three experimental dietary groups, only attained similar body masses to free-living chicks despite being given 1.9 times as heavy meals as shearwater parents provided to their free-living chicks. This evidence indicates that in order for free-living Short-tailed Shearwater chicks to grow to obesity, they depend on a far higher energy intake than that available in their diet alone. The specific oil, accumulated in the shearwater parents' proventriculus, and delivered to the chick, is an important contribution. In other words, digestible prey, such as krill, and parental stomach oil, are both essential to insure obesity for Short-tailed Shearwater chicks.
The Grey-faced Buzzard (Butastur indicus) is a migratory raptor breeding in Japan. It has a high breeding density in what is known as “Satoyama”, a traditional mosaic landscape of paddy fields, woodland, grassland, and streams. We studied the foraging behavior of five buzzard pairs in Satoyama of Tochigi Prefecture, central Japan, for two years. Seasonal changes in foraging sites and differences in the amount of prey captured at each foraging site were analyzed by Bayesian inference using a Markov Chain Monte Carlo (MCMC) algorithm. The main vegetation types which characterized the foraging areas of the buzzards varied over the course of the breeding season from paddy fields to levees and grass-arable fields, and eventually to wooded areas. Along with this shift, the main prey of the buzzards changed from frogs to insects. In paddy fields, frogs and small mammals were frequently captured. A variety of prey including frogs, small mammals, lizards, snakes, and insects were taken at levees and grass-arable fields. Insects and frogs were captured in woodland areas. Since the buzzards utilized almost all vegetation types found in Satoyama when foraging, spatial distribution of these foraging sites and the prey biomass therein need to be considered when planning the conservation of breeding habitat for this species.
Recently, to help curb anthropogenic climate change and fossil fuel depletion, there has been a rapid increase in the number of wind farms being built worldwide. However, the construction of wind farms in the foraging areas of raptors or along the routes of migratory birds raises concerns about avian collisions and habitat loss. Here, we present an additional situation in which avian collisions may present a problem. That is, when wind farms are built between roosting and foraging areas of over wintering migratory birds, the bird flocks are forced to pass through the farm each morning and evening. Indeed, at the Awara Wind Farm in Fukui Prefecture, Japan, approximately three thousand White-fronted Geese Anser albifrons frontalis inhabit the site where the installation of 10 wind turbines has recently been completed. The collision risk posed by these turbines may affect the goose population. However, few studies have examined the effects of wind farms on the flight patterns of geese, making it difficult for stakeholders to achieve a consensus. The purpose of this study was to evaluate the collision risk for geese in the planning phase of the Awara Wind Farm. A collision model based on goose avoidance behavior was developed to predict collision mortality, and an applied potential biological removal (PBR) analysis was used to determine the maximum allowable collision mortality (ACM) whilst maintaining a sustainable goose population. The estimated annual collision mortality was 0-2 geese, whereas the allowable collision mortality was 75 geese per year, suggesting that the collision risk is sufficiently small for the population to persist. We also include a discussion of adaptive management plans for regulating wind turbine operations when the actual collision mortality exceeds the socially acceptable level.
Estrildine finches are important model species in experimental studies on female mating preferences, but research has focused on only two species from this family, namely, the Zebra Finch Taeniopygia guttata and the Bengalese Finch Lonchura striata var. domestica, and we know comparatively little about other closely related species. Therefore, we investigated sexual dimorphism and female choice in the Java Sparrow Padda oryzivora, which also belongs to the family Estrildidae, to open up the potential for comparative research and to better understand sexual selection in this family. First, we took measurements of eight morphological traits of six male and six female Java Sparrows: natural wing length, maximum wing length, tarsus length, tail length, exposed culmen length, bill width, bill depth and body mass. We quantitatively confirmed that Java Sparrows show sexual dimorphism in bill depth, with males having deeper bills than females. Second, we examined individual variation in male courtship songs by analyzing their acoustic and syntactical structure. After collecting data on male morphological and song-related traits, we conducted two-way choice tests to ask which kinds of male traits predicted which males were preferred by female Java Sparrows. In the choice tests, we put a cage with a female in between two cages each containing one male and recorded the position of the female every 30 seconds by point sampling. We performed a stepwise regression analysis to assess the relationship between the time females spent in front of each male and male morphological and song-related traits. The results indicated that females base their preference upon large body size, which is likely to act as a good indicator of male quality. However, no preference was observed for song-related traits or sexually dimorphic bill depth. Perhaps the sexual dimorphism in bill size is instead the evolutionary outcome of male-male competition.
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