Yuji Okahisa

Breeding seasons of landbirds in New Caledonia

Abstract Based on 805 observations of 63 species, we identified the main breeding seasons of avian trophic guilds in New Caledonia. Most omnivorous and carnivorous birds had undefined breeding periods with moderate peaks during the warm/dry season and the hot/rainy season. In contrast, nectarivorous, frugivorous, granivorous and insectivorous species had marked breeding seasons that started at the beginning of the warm/dry season and ended in the hot/rainy season. Introduced species also reproduced during these periods, regardless of the trophic guild to which they belonged.

Mating system and extra-pair paternity in the Fan-tailed Gerygone Gerygone flavolateralis in relation to parasitism by the Shining Bronze-cuckoo Chalcites lucidus

Extra-pair copulation can increase genetic diversity and offspring fitness. However, it may also increase intra-nest variability in avian hosts of brood parasites, which can decrease the discrimination ability of host parents towards the parasite. In New Caledonia, the Fan-tailed Gerygone (Gerygone flavolateralis), which is parasitized by the Shining Bronze-cuckoo (Chalcites lucidus), has two nestling morphs, dark and bright, that can occur in monomorphic and polymorphic broods. Gerygone parents recognize and eject parasite nestlings from their nest, but the presence of polymorphic broods may increase the chances of recognition errors. Using 17 microsatellite markers, we investigated the mating system of the Fan-tailed Gerygone to understand the mechanisms underlying nestling polymorphism. We hypothesised that extra-pair copulations would lead to a higher proportion of polymorphic broods caused by higher genetic variability, thus creating a trade-off between genetic benefits and host defence reliability. Extra-pair paternity occurred in 6 of 36 broods, which resulted in 6 of 69 offspring sired by extra-pair males. Broods with and without mixed paternity were comparably often parasitized. Extra-pair paternity did not influence the proportions of bright, dark and polymorphic broods. Compared to bright siblings in polymorphic broods, dark nestlings tended to have lower heterozygosity, particularly in loci associated with skin coloration. The results also suggested that there is no obstacle for genetic exchange between individuals from forest and savannah, possibly due to dispersal of offspring. We conclude that the Fan-tailed Gerygone is a socially monogamous species with a low rate of extra-pair paternity compared to closely related species. Extra-pair paternity increased offspring genetic variability without measurable associated costs by brood parasitism. The results highlight the importance of studying host mating systems to assess the trade-offs between host defence and offspring fitness in co-evolutionary arms races.

Using playback and habitat models to estimate the distribution and population size of the critically endangered Crow Honeyeater, Gymnomyza aubryana, in New Caledonia

Abstract The Crow Honeyeater (Gymnomyza aubryana) is a critically endangered bird, endemic to the main island of New Caledonia, but it is poorly known owing to its elusive nature. We conducted playback surveys to assess the distribution, habitat preferences and vocal activity of the species. Crow Honeyeaters responded well to playback, with response rates reaching 67% at times. Our surveys revealed two distinct populations, separated by ∼250 km: one in the north of the island and the other, larger population in the south. The range of the northern population appears to be very small. Presence of the species was linked to rainforests growing on oligotrophic soils, primarily on ultramafic substrates. Approximately 315–700 km2 of suitable habitat for the species remains, corresponding to a maximum estimated population of 315–700 breeding pairs. The size and range of the Crow Honeyeater population is much smaller than previously assumed, and comprehensive management will be required to ensure its survival.

Establishment of Microsatellite Markers to Assess the Mating System of the Fan-Tailed Gerygone (Gerygone flavolateralis) for Studying Cuckoo-Host Arms Race

We developed a set of microsatellite markers for the fan-tailed gerygone (Gerygone flavolateralis), host of a brood parasite, the shining bronze-cuckoo (Chalcites lucidus). We used 454 pyro-sequencing to establish 17 polymorphic microsatellite markers. The number of alleles per locus ranged from 6 to 18, the expected heterozygosity from 0.328 to 0.931 and the polymorphism information content from 0.306 to 0.916. The developed set of microsatellites will allow us to determine the gerygones mating system, which is crucial to understand inheritance of dichromatism in skin colour of their chicks.

Gourmand New Caledonian crows munch rare escargots by dropping

Numerous broken shells of a rare endemic snail Placostylus fibratus, a species rated as vulnerable, were scattered around rocky beds of dry creeks in rainforest of New Caledonian. We set a video camera near one site to identify the predator. We recorded a New Caledonian crow Corvus moneduloides dropping and consuming the snail. This is the first direct evidence of the crow dropping of this native species. The assumed weight of snails relative to the crow is exceptionally heavy among prey dropped by birds.

Effect of pre-breeding moult on arrival condition of yearling male Narcissus Flycatchers Ficedula narcissina

Capsule Moult of greater coverts in the wintering area is correlated with a decrease in spring arrival condition but not arrival time of yearling male Narcissus Flycatchers.

Visual discrimination of polymorphic nestlings in a cuckoo-host system

Mimicry by avian brood parasites favours uniformity over variation within a breeding attempt as host defence against parasitism. In a cuckoo-host system from New Caledonia, the arms race resulted in both host (Gerygone flavolateralis) and parasite (Chalcites lucidus) having nestlings of two discrete skin colour phenotypes, bright and dark. In our study sites, host nestlings occurred in monomorphic and polymorphic broods, whereas cuckoo nestlings only occurred in the bright morph. Irrespective of their brood colour, host parents recognised and ejected parasite nestlings but never ejected their own. We investigated whether host parents visually recognised their own nestlings by using colour, luminance and pattern of multiple body regions. We found that the parasite mimicked multiple visual features of both host morphs and that the visual difference between host morphs was larger than the difference between the parasite and the mimicked host morph. Visual discrimination alone may result in higher chances of recognition errors in polymorphic than in monomorphic host broods. Host parents may rely on additional sensorial cues, not only visual, to assess nestling identity. Nestling polymorphism may be a trace of evolutionary past and may only have a marginal role in true-recognition of nestlings in the arms race in New Caledonia.

Puddle use by New Caledonian rainforest birds

Abstract 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 Nest Sites and Nest Characteristics of Narcissus Flycatcher Ficedula narcissina

Abstract Although Narcissus Flycatchers readily use nest boxes, natural nest sites and nest characteristics have not previously been described. The location of 41 Narcissus Flycatcher nests and data on the dimensions of 17 nest holes in the Fuji Primitive Forest of Japan are described. Japanese Hemlocks were the most commonly chosen tree species for nesting although 14 other tree species were also used and no significant nest tree species preference was observed. Nests (classified as either half cavity, full cavity, chimney, or shelf), were built at an average height of 7.3 m. Flycatchers tended to nest in dead trees or trees with trunks greater than 20 cm in diameter (mean 30.9 cm). Nests were typically made from dead leaves, moss, plant fibers, and animal hair. This is the first description of natural nest sites and nest characteristics of Narcissus Flycatchers; details are compared with those of other closely related flycatcher species.