Displays of animals do not always elicit equivalent responses from other conspecifics. Considerable variation exists among the responses, but the mechanism causing the variety remains unclear. We investigated how Black-tailed Gulls Larus crassirostris respond to long-call displays of other individuals. Results show that the response varies depending on the context. Territorial birds often respond to the long-calls of non-territorial birds by attacking. However, non-territorial birds typically respond to the long-calls of territorial birds by avoiding them. Nevertheless, they usually respond to the long-calls of their partners by using the same long-call. These results are explained well by the motivational conflict hypothesis.
Recent research into the Large-billed Gerygone, a host species of the Little Bronze-Cuckoo, has revealed that the host physically ejects parasitic cuckoo young from its nest, a behaviour not previously observed in any other host-brood parasite system. Curiously, this host does not reject dissimilar foreign eggs despite egg rejection seeming to be a better strategy for it because if successful, there is no risk of the warbler's own eggs being ejected by cuckoo young. In order to explain this puzzle, we present a new hypothesis, termed the egg dilution effect, which argues that parasitic cuckoo eggs serve to ensure host egg survival through the dilution effect and protect against parasitism by multiple females. It is therefore beneficial for hosts to accept cuckoo eggs even if they are capable of discriminating cuckoo eggs from their own. The conditions of this hypothesis, such as small clutch size and high parasitism rate, fit the nature of the host species and thus help explain why this unique anti-parasitic strategy has evolved only in the Large-billed Gerygone.
In the course of our fieldwork study at Hyo-ko Waterfowl Park, a local preserve in Niigata Prefecture, Japan, we found a male presumed wild hybrid between a Eurasian Wigeon Anas penelope and a Falcated Duck A. falcata in 2007; another or possibly the same individual was found again in 2009. The bird shared morphological traits with both species, although it was biased toward the Falcated Duck. Occasionally, the bird joined courting parties of Eurasian Wigeon, followed Wigeon females or competed with Wigeon males, and also showed courtship displays, e.g. Grunt-whistle, Head-up-tail-up, and Burping call, all of which were more like those of the Falcated Duck than those of the Eurasian Wigeon. Thus, the hybrid bird was sexually active to a considerable extent, but it remains unknown whether or not it actually formed a pair bond with a female of either parent species.
We studied the breeding biology of the Japanese Night Heron Gorsachius goisagi from 21 June to 2 August 2009. This species was previously considered an endangered endemic breeding species of southern Japan only, but was found breeding in a valley at the bottom of Mt. Halla at Ara-dong, Jeju City, the southernmost island of Korea. This marks the first record of this species ever to be found breeding in Korea. The forested area consisted predominantly of plants such as Morus bombycis, Cryptomeria japonica, Styrax japonica, Orixa japonica, Viburnum dilatatum, and Lindera erythrocarpa. Materials for the nest were largely M. bombycis, followed by S. japonica, C. japonica, and so forth. There were three eggs in the clutch, and the brooding period lasted for 42 days. A close look into the pellets demonstrated that their main prey items were earthworms, snails, and cicadas. The results of this study represent valuable data, allowing for the mapping out of new methods for managing Gorsachius goisagis, a species currently on the brink of extinction.
This study compared microhabitat characteristics among nesting, foraging, and singing sites of the Gray-cheeked Fulvetta Alcippe morrisonia in the Fushan Experimental Forest, northeastern Taiwan. Habitat variables, including height above ground, vegetation level, vegetation density at locations where these three types of behavior occurred, and structure, height and diameter at breast height (dbh) of the plant used were recorded from March to July of 2002. The Gray-cheeked Fulvetta predominantly nested in bushes and among herbs (86.7%), but usually foraged and sang in trees (70.8% and 78.3%, respectively). Consequently, significant differences were found in the structure of plants and vegetation level used among nesting, foraging, and singing behavior. Gray-cheeked Fulvettas built their nests at an average height of 1.05 m; however, they foraged around 3.75 m and sang at 5.30 m above ground. On the other hand, nests were situated within the most concealed area, with an average vegetation density of 74%, significantly greater than those of the foraging and singing sites (45%, 38%, respectively). The differential use of microhabitat among these three types of behavior strongly exhibits the divergent adaptation of different behaviors to a bird's environment. This is the first report on habitat selection of various behaviors of the Gray-cheeked Fulvetta, and will contribute to our understanding of the species' dominant role in most lowland forests in Taiwan.
The maintenance of multiple ornaments by animals can be explained when those multiple ornaments are sexually selected. However, there have been only a few studies of sexual selection on multiple ornaments. We investigated sexual selection on two ornaments, plumage coloration and white spots in the tail, in a population of Barn Swallows Hirundo rustica gutturalis in Japan. There was sexual dimorphism in throat coloration and in the size of the white spots in the tail. Males with a less saturated (colourful) throat and larger white spots in the tail bred earlier than others, indicating a mating advantage for these males. These trends are what would be expected if these ornaments were indeed sexually selected.
Changes in body mass of a pair of captive Japanese Rock Ptarmigan Lagopus mutus japonicus and their chicks were measured using an automatic weighing system at Omachi Alpine Museum from 13 January 1995 to 29 October 1996. The male's body mass decreased gradually in late April, the beginning of the breeding season, but returned to the normal level in the fall. In contrast, the female's body mass increased rapidly from late April onward, peaking in late May, just before the egg-laying period. Thereafter, the female's body mass decreased throughout the egg-laying, incubation, and early brooding periods, but began to increase again in the fall. In 1996, four chicks were successfully reared and their body mass increased linearly during the first 60 days after hatching, followed by a milder increase.
The proportion of full songs (Pfs) in the song bout of a male Grey Thrush Turdus cardis indicates its desire to attract females. At dawn, male Grey Thrushes make trips away from their usual singing areas. In this study, I assessed the distance of the song points from the nest in relation to the Pfs. Song points with a high Pfs (mainly at dawn) were farther from the nest than those with a low Pfs (during daytime). I conducted playback experiments to compare territorial behavior between dawn and daytime singing areas. Responses were strong in the daytime singing area, but weak in the dawn singing area. It appears that male Grey Thrushes make dawn trips to attract second mates.
On average, male birds other than social father sire more than 10% of all offspring. Levels of extra-pair paternity below 5% of offspring are rarely found and are now considered worthy of explanation in monogamous birds. We recorded the lowest levels of paternity loss ever reported in a population of Barn Swallows Hirundo rustica. The levels of extra-pair paternity were below 5% of offspring (7/243 in 2005 and 1/53 in 2006). We discuss our results in relation to the density-dependence of extra-pair paternity.