Birdsong is an important sexually selected trait, and its acoustic features are socially transmitted in the process of song learning. Though a great deal of research has been conducted to shed light on the mechanisms and functions of song learning, we still do not have clear answers as to why for some species, including Estrildid finches and humans, the ability of “social” vocal learning has evolved. Therefore, this paper addresses social factors responsible for song learning, especially focusing on tutor choice in Estrildid finches, with the aim of elucidating what is already clear about how the social environment shapes songs and what is needed in future studies.
Density, movements, daily activity and behaviour of a wintering population of Siberian Grouse Falcipennis falcipennis was studied on radio-tagged birds in the Lower Amur region, 100 km North of Komsomol'sk (Khabarovsk region). For this species, the wintering period lasts 7–7.5 months – from October through April. Best wintering habitats occur in the middle and upper parts of slopes with tracts of mature spruce forests, dying stems and small openings surrounded by spruce-fir undergrowth. From January through March adult cocks occupy areas of 19.5±13.9 ha, females 26.5±17.3 ha; subadult cocks 128±70.5 ha, and subadult hens 151±22.9 ha. Although typically occurring in groups of 2–3 birds, by the end of winter, flock size increases to 4–6; winter aggregations averaged 3.06 birds, but up to 48% of encounters were with single individuals. Winter conditions do not interrupt numerous social contacts within the local population. The birds elaborate cryptic behaviour, its unwillingness to land on snow in daytime and the various precautions it takes to avoid disturbance, clearly indicate that the pressure of predation is a constant force with which the species has to cope.
To understand seasonal declines of investment in egg production, we studied the relationships among laying date, clutch, and egg sizes in a Great Cormorant Phalacrocorax carbo population. Seasonal changes in the amount and number of fish caught per casting net were used as an index of food abundance for Great Cormorants. Clutch size and egg volume were positively correlated and decreased as the breeding season progressed. Clutch volume (i.e. total egg volume within clutches) was explained by clutch size and laying date. However, the amount and number of fish caught per casting net increased through the season. We conclude that the observed seasonal decline in egg production investment was not a result of declining food abundance during the breeding season in Great Cormorant. The amount of egg investment appeared to depend on the fishing ability of the individual rather than fish availability during the breeding season. Early in the breeding season, only those individuals with strong fishing abilities would be able to acquire sufficient nutrition to lay eggs. Thus, egg investment and food abundance are expected to show opposite seasonal trends.
To describe the life history of an endangered insular subtropical subspecies of the Common Buzzard Buteo buteo toyoshimai, we studied its breeding biology on Chichijima, Ogasawara Islands in the Pacific Ocean. Several nests were found in single territories, most of them located on cliffs. Social behavior reached peaks in winter, during December and February. Copulation between paired mates occurred from January to June. Egg laying was estimated to begin in late January, and lasted a minimum of two months. Incubation ranged from 30 to 33 days and the nestling period from 33 to 45 days. Both females and males incubated the eggs, but only females brooded the nestlings. Both sexes brought prey to the nest; however, only females fed prey directly to their young nestlings. Within two weeks of hatching, the time spent by females at the nest decreased to less than 50% of the observation time. The means of clutch, early brood (1–3 weeks), late brood (>4 weeks), and fledgling sizes were 2.2, 1.8, 1.3, and 1.2, respectively. Brood reduction occurred in nests containing several nestlings. Some fledglings depended on their parents for several months, staying in their parents' territories until October. The breeding success rate in terms of the proportion of pairs with fledglings was 0.35. These results suggest that the sub-tropical Ogasawara race of the Common Buzzard is socially monogamous and has a distinct breeding season.
Oriental Honey Buzzards (Pernis ptilorhynchus) are birds of prey that mainly feed on the larvae of social bees and wasps. Previous researchers noted that they have an unusual morphology and it is proposed that this is adaptive to their diet and feeding behaviour. In this study we aimed to quantitatively identify key features of Oriental Honey Buzzards that distinguished them from other birds of prey using morphometric methods. Eighty museum specimens of Japanese raptors (13 Oriental Honey Buzzards, 9 Grey-faced Buzzards, 13 Black Kites, 12 Northern Goshawks, 12 Common Buzzards, 12 Mountain Hawk-eagles and 9 Ospreys) were measured and photographed. PCA analysis, based on 11 head and 11 foot measurements, and landmark based relative warps analysis combined with canonical variates analysis were used to describe morphological variation among the specimens and identify which morphological characters were most important in distinguishing Oriental Honey Buzzards from the other species. We found that the honey-buzzards had a distinctive head morphology, with a long cere and long slit-like nares, and a longer, thinner beak that had a shorter hook at the tip. In relation to their foot size, honey-buzzards had a longer Digit-II and shorter Talon-I and Talon-II than all other species in the study. Long Digits III and IV and shallow tendon depth on the toe were also important in distinguishing Oriental Honey Buzzards from the other species. We suggest that a long, thin beak with a short hooked tip and long digits on the feet are adaptive for extracting larvae from combs and digging wasp nests out of the ground, while the slit-like nares and long cere may offer protection from stings. Identifying key morphological features using morphometric methods allows us to better understand the adaptations and evolutionary processes associated with feeding behaviour in birds of prey.
Sex determination is often difficult in small seabirds in the field. External measurements and feather coloration were compared between 23 male and 24 female Swinhoe's Storm Petrels Oceanodroma monohris, following molecular sex determination. No sex differences were detected in any of the nine size parameters. Although females exhibited higher ultraviolet and visible color reflectance from the abdomen feathers and males exhibited higher visible reflectance from the crown feathers, these sexual differences in coloration were barely detectable. These results suggest that neither external measurements nor coloration are reliable for sex determination in this species.
We identified the diet of owlets of the Daito subspecies of the Ryukyu Scops Owl Otus elegans interpositus on Minami-daito Island during late May and early June 2009, by means of high-resolution color photography. Cockroaches were provided by parents to their young at all eight nests studied, and contributed the largest single component of the diet (33%). Orthoptera species, which inhabited open grassland habitats, constituted >20% of the total occurrences in the diet of owlets. It is suggested that Ryukyu Scops Owls depend heavily on food items obtained from habitats that have been modified by human activity on Minami-daito Island. Diets for owlets differed widely among nests, and the differences were considered to result from individual differences among parents and/or the environments surrounding each nest.