Noriyuki Yamaguchi

Extra-pair mate choice in the female great tit Parus major: Good males or compatible males

The good genes hypothesis and the genetic compatibility hypothesis are the two main hypotheses that focus on the genetic benefit that a female can gain through her choice of a mate. We tested the two hypotheses on extra-pair mating in the great tit, Parus major. We found that female great tits choose males on the basis of breast stripe width, which is in accordance with the good genes hypothesis. Although females chose less related extra-pair males, the evidence for female choice for compatible males was overall weak. However, our data suggest a post-copulatory mechanism of inbreeding avoidance. The observed individual inbreeding coefficient, F, was similar for within-pair offspring (WPO) and extra-pair offspring (EPO). The observed individual F of WPO was lower than the expected individual F, whereas the observed F of EPO was similar to what was expected. These results highlight the importance of processes after copulation for the outcome of female mate choice. Our study shows that in a system with apparent pre-copulatory female choice for good genes, a post-copulatory mechanism may still promote the production of offspring that carry compatible genes.

Plumage color as a status signal in male-male interaction in the red-flanked bushrobin, Tarsiger cyanurus

Recent studies have suggested that structural-based coloration is an honest signal of male genetic and/or conditional quality in sexual selection. However, whether structural coloration functions in intrasexual competition is unknown. We examined whether plumage color functions as a status signal during intrasexual interactions in the red-flanked bushrobin Tarsiger cyanurus; adult males have many blue plumes as structural coloration whereas yearling males and females are olive brown with few blue plumages. Blue males did not always dominate olive-brown males. The number of interactions did not differ with the colors of the two birds involved. The interactions of a blue male and an olive-brown male were less aggressive than those of two blue or of two olive-brown males. In this study, we found that structural plumage coloration may serve as a signal of aggressive intent and lower the escalation level of an aggressive interaction in a manner consistent with hypotheses regarding the evolution of delayed plumage maturation.

Social structure and helping behaviour of the Grey-crowned Babbler Pomatostomus temporalis

A 4-year study of cooperative breeding in the Grey-crowned Babbler Pomatostomus temporalis was conducted in the monsoon-tropics of northern Australia. Most groups comprised a single socially monogamous pair with up to seven helpers. We found no floaters. The sex ratio was almost unity for each year. Helpers included philopatric offspring, immigrating juveniles and immigrating sexually mature birds. Adults of both sexes moved frequently between groups. Pairs without helpers were unable to raise young to fledging and often divorced, suggesting that cooperative breeding was obligatory in this population. However, for groups with helpers, the group size effect was weak; there was no significant correlation between the number of fledglings and number of helpers. Breeding females exclusively contributed to incubation. Breeders contributed more to provisioning of nestlings than non-breeders. Although helpers did not enhance the total provisioning rate to nestlings, small groups should recruit helpers to maintain the group and enhance reproductive success.

Satellite tracking of migrating Whooper Swans Cygnus cygnus wintering in Japan.

Abstract We satellite-tracked Whooper Swans Cygnus cygnus wintering in northern Japan to document their migration routes and timing, and to identify breeding areas. From 47 swans that we marked at Lake Izunuma-Uchinuma, Miyagi Prefecture, northeast Honshu, and at Lake Kussharo, east Hokkaido, we observed 57 spring and 33 autumn migrations from 2009–2012. In spring, swans migrated north along Sakhalin Island from eastern Hokkaido using stopovers in Sakhalin, at the mouth of the Amur River and in northern coastal areas of the Sea of Okhotsk. They ultimately reached molting/breedmg areas along the Indigirka River and the lower Kolyma River in northern Russia. In autumn, the swans basically reversed the spring migration routes. We identified northern Honshu, eastern Hokkaido, coastal areas in Sakhalin, the lower Amur River and northern coastal areas of the Sea of Okhotsk as the most frequent stopover sites, and the middle reaches of the Indigirka and the lower Kolyma River as presumed breeding sites. Our results are helpful in understanding the distribution of the breeding and stopover sites of Whooper Swans wintering in Japan and in identifying their major migration habitats. Our findings contribute to understanding the potential transmission process of avian influenza viruses potentially carried by swans, and provide information necessary to conserve Whooper Swans in East Asia.

Seasonal shifts in foraging site and prey of Grey-faced Buzzards (Butastur indicus), breeding in Satoyama habitat of central Japan

Abstract 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.

Factors causing variation in flock size: Decision making to join a foraging flock

In order to clarify the temporal variation of flock size, we examined factors that cause the temporal variation of foraging flock size in a wintering population of the Yellow-throated bunting (Emberiza elegans). We conducted field observations to examine whether the flock size varies greatly and whether non-random associations between individuals exist. We confirmed that flock size varied greatly and some individuals showed non-random associations with other flock members. Then, we carried out computer simulations that assume stochastic risky situation, the condition of hunger level and non-random associations between individuals. In the simulation, the condition of hunger level caused the variation of flock size. However, the distribution of flock size differed from observed ones. When the condition of non-random association was added to the simulation, the variation of flock size became large and the distribution of flock size was similar to that of the observed one. In wintering flocks of Yellow-throated bunting, each individual attempts to forage in an optimal flock size. However, if they are extremely starved, it is suggested that they adopt a conditional strategy to join a flock independently of the flock size to acquire the energy necessary for survival. Simultaneously, they may decide to forage under the effect of non-random association between individuals.

The effects of nest usurpation and other interference by the Blue-faced Honeyeater on the reproductive success of the Grey-crowned Babbler

Abstract Nest-building is a costly activity and natural selection may sometimes favour usurpation of existing nests. Few quantitative studies have investigated the effect of usurpation of nests on the reproductive success of the usurped species. Here we studied 27 instances of usurpation of Grey-crowned Babbler (Pomatostomus temporalis) nests (n = 310 nests) by Blue-faced Honeyeaters (Entomyzon cyanotis) in the monsoon tropics of Australia between 2003 and 2008. When usurpation occurred during laying or incubation the Babbler eggs disappeared. The frequency of nest usurpation by Blue-faced Honeyeaters varied between Babbler territories, from no usurpation to almost every year during the study period. Based on video-recording at Babblers’ nests over 854 days, we observed 75 interference events on 39 days at 29 nests. Interference occurred most frequently during nest-building and incubation and much less frequently in the nestling stage. Modelling suggested interference by Honeyeaters can have severe effects on breeding of Grey-crowned Babblers, with success of individual nests reduced by 52.5% during the nest-building stage, 25.9% during incubation, and 1.2% during the nestling stage. Babbler group size did not affect the occurrence of interference. The southern subspecies of Grey-crowned Babbler is declining and it is conceivable that populations could be adversely affected by interference from Blue-faced Honeyeaters in areas where the two species co-occur.

Spatial Structure and Colonization Process of Varied Tit Populations in the Izu Islands

Abstract The Izu Islands of Japan are a geographically young volcanic archipelago nearer to the mainland than other islands used in speciation studies, such as the Galapagos Islands of Ecuador. On the Izu Islands, birds are likely to have undergone recent colonization and trait diversification. Three morphological groups of Varied Tits, Poecile varius, breed on the islands. The varius group, which has the smallest body size and is the same as that found on the mainland, breeds on the northernmost island (closest to the mainland). The namiyei group, which has an intermediate body size, breeds on two or three central islands, and the owstoni group, which has the largest body size, is found on several southern islands. To infer the gene flow ranges and colonization processes of Varied Tits with such obvious trait polymorphisms among the Izu Islands, we analyzed the genetic population structures of these three morphological groups. In genetic analysis of all samples, individuals were first divided into cluster A, which was composed of individuals from Kohzu Island (a central island) from the namiyei group, and cluster B, which was composed of individuals from mainland sites and other islands (excluding Kohzu and Niijima). The genetic characteristics of individuals from Niijima may indicate a recent gene flow event between clusters A and B. Individuals from the owstoni group were genetically similar to varius group individuals, despite the large distance between the breeding areas of these two groups. The second step of our analysis used samples from cluster B. These samples were grouped into three clusters, one of which was further classified into two clusters in our third-step analysis. In conclusion, we detected a hierarchical structure among Varied Tits breeding on the Izu Islands and inferred that ancestors of the owstoni group colonized from the mainland more recently than those of the namiyei group.