Masaoki Takagi

Some effects of inclement weather conditions on the survival and condition of bull‐headed shrike nestlings

Inclement weather struck Japan in 1993, permitting a natural experiment for examining the effect of weather conditions on nesting success and nestling growth of the bull-headed shrike, Lanius bucephalus. Aspects of the breeding biology of bull-headed shrikes in relation to weather conditions and timing of breeding in 1992 and 1993 were examined. The two breeding seasons were divided into two periods, early and late, in each year. While the probability of nest survival in nestling stages during both periods was almost equal, the probability of nest survival in the egg stage during the early period was significantly lower than that during the late period. In 1993, the probability of nestling survival during the late period was significantly lower than during the early period; the late period had larger fluctuations of precipitation and was colder than the same period in 1992. The number of ‘disappeared’ nestlings positively correlated with mean precipitation per day. The greater part of the disappeared nestlings was the lightest in each brood. Late breeders fledged lighter young than the early breeders. Although shrikes adopted hatching asynchrony, the late breeders could not surmount the unpredictable inclement weather in 1993.

Philopatry and habitat selection in Bull-headed and Brown shrikes

Abstract Philopatry and habitat selection were examined for migratory populations of the two sympatric shrike species, the Bull-headed (Lanius bucephalus) and Brown (L. cristatus) shrikes in northern Japan between 1992 and 1997. Although 18% of banded Bull-headed Shrike males returned to the previous breeding area, no female did. In Brown Shrikes, 43% and 13% of banded males and females, respectively, returned to the area. Brown Shrikes are significantly more philopatric than Bull-headed Shrikes. Even successful breeders in Bull-headed Shrikes did not always return to the area near their nesting site of the previous year. Successful breeders in Brown Shrikes were faithful to their past breeding site. Brown Shrikes decreased by 67% due to habitat loss over four years, while the population of Bull-headed Shrikes was stable. The degree of philopatry was inconsistent with the population trends of the two shrikes. While Bull-headed Shrikes did not have habitat preferences in the study area, Brown Shrikes bred mainly in natural grasslands with shrubs. Since available habitat for Brown Shrikes has decreased rapidly in and near the study area, the philopatry of Brown Shrikes may result from a scarcity of habitat that inhibits dispersal. Bull-headed Shrikes may have a higher tendency to disperse because they are habitat generalists. With its more narrow requirements, the Brown Shrike appears to have suffered significantly from habitat loss, while the Bull-headed Shrike has not been adversely affected.

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.

Change in body mass in relation to breeding phase in bull-headed shrikes

Changes in body mass of both sexes of the bull-headed shrike, Lanius bucephalus, were investigated over the six breeding phases of this species. Standardized body mass (SBM), which was defined as body mass divided by the length of the tarsus, of the males was relatively constant over the phrases, while the SBM of the females changed drastically. In the females, the SBM during egg-laying was higher than the SBM in all the other breeding phases. The SBM of the females did not differ between the incubation and early-nestling phases, and was lowest during the fledgling phase. Mass loss in bull-headed shrikes did not correspond to an adaptive adjustment of body mass to permit a reduction in the power required for flight in the nestling period. It is likely that incubating females constantly maintain their body mass to invest in parental efforts from the incubating to nestling periods.

Harmful effects of invasive Yellow Crazy Ant Anoplolepis gracilipes on three land bird species of Minami-daito Island

Abstract This report describes, for the first time, harmful effects of invasive Yellow Crazy Ants Anoplolepis gracilipes on wild birds in Japan. We observed fledglings of Bull-headed Shrike Lanius bucephalus and Daito White-eye Zosterops japonicus daitoensis caused fatal injuries by ants on the ground on Minami-daito Island. We compared reproductive behaviors of Daito Scops Owl Otus elegans interpositus in a cavity with ants and cavities without ants and found that while reproductive success did not differ between them, parental females in a cavity with ants more frequently interchanged their nest site than those in cavities without ants.

Status of the Daito Scops Owl on Minami-daito Island, Japan

Estado De Otus Elegans Interpositus En La Isla Minami-daito, Japon Otus elegans esta listada en la Lista Roja de Especies Amenazadas del 2004 de la UICN como casi amenazada, y la subespecie O. e. interpositus esta listada como en peligro en el Libro Rojo de Datos de Okinawa. O. e. interpositus es endemica de las Islas Minami-daito y Kita-daito, las cuales se localizan a 360 km de la Isla Okinawa (25°50′N, 131°14′E), Japon. Desde el 22 de marzo al 12 de mayo de 2005, contamos el numero de machos que respondieron a llamadas reproducidas en la Isla Minami-daito. Confirmamos la presencia de 245 machos, 155 de los cuales respondieron en duetos con las hembras. Basandonos en dos calculos diferentes de la probabilidad de deteccion, estimamos que el numero de parejas fue de 199 o 210. Esta especie probablemente se encuentra cerca de su capacidad de carga en el area de refugios de la Isla Minami-daito. Cualquier reduccion del numero de refugios probablemente provocara la disminucion del numero de individuos de est...

Within- and among-clutch variation in maternal yolk testosterone level in the Black-tailed Gulls Larus crassirostris

Abstract 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.

Drastic decline of territorial male Daito Scops Owls on Minami-daito Island in 2006

the 2004 IUCN Red List of Threatened Species as Near Threatened (BirdLife International 2004). Four subspecies of Elegant Scops Owls are recognized, composed of many separate island populations (see Köning et al. 1999). One of these subspecies, the Daito Scops Owl (O. e. interpositus) is endemic to Minamiand Kita-daito Islands, 360 km off Okinawa Island (25°50 N, 131°14 E) in Okinawa prefecture (Ornithological Society Japan 2000). The Daito Scops Owl is also listed as Endangered in the Red Data Book of Okinawa (Okinawa Prefecture 1996). The population on Kita-daito Island was considered to have been extirpated (Kenji Takehara & Kazuo Nakamura personal communication), while the number of male Daito Scops Owls was estimated to be 245 on Minami-daito Island during the 2005 breeding season (Takagi et al. 2007). Research on the same island in 2006 revealed a drastic decline in the number of Daito Scops Owls on Minami-daito Island. The purpose of this study was to describe the population on Minami-daito Island in 2006, and to discuss population estimates of Daito Scops Owls.

Direct impact of typhoons on the breeding activity of Bull-headed Shrike Lanius bucephalus on Minami-Daito Island

regions, climatic disasters (e.g., droughts and cyclones) sometimes impact avian populations (Boag & Grant 1981; McCallum et al. 2000). Tropical cyclones (e.g., hurricanes, cyclones, and typhoons) are assumed to cause breeding failure amongst birds because inclement weather conditions reduce nestling growth and lead to starvation (Takagi 2001). Although disturbance by storms is known to affect bird populations indirectly through modifications of habitat structure and changes in food abundance after storms (e.g., Levey 1988; Wunderle et al. 1992; Wunderle 1995; Seki 2005), there have been few descriptions of direct damage caused by tropical cyclones to active nests in which parent birds were incubating clutches or rearing young (but see King et al. 1992). A continuous population study (since 2002) of Bull-headed Shrikes Lanius bucephalus on the small oceanic island of Minami-Daito in the northwest Pacific has shown that the main breeding season lasts for approximately six months from mid-February to mid-August (Shin Matsui & Masaoki Takagi unpublished). During this time, there are two peaks of breeding activity the first in early April followed by a second in early June, with almost all young fledging by the end of July (Shin Matsui & Masaoki Takagi unpublished). An average of 1.06 typhoons hit Minami-Daito island annually (1955–2003) by the end of July, namely during the Bull-headed Shrike’s breeding season (http://www.okinawa-jma.go.jp). The intensities of the typhoons that approached the island during the breeding seasons were usually weak (as classified by their maximum wind speeds; Okinawa Meteorological Observatory 1998; http://www. okinawa-jma.go.jp), however, two exceptionally strong typhoons approached the island in May and June 2004, and heavy nest-losses occurred in the late breeding season of that year. In this paper, we report on breeding failure amongst Bull-headed Shrikes in relation to the two typhoons.

A Typological Analysis of the Hoot of the Ryukyu Scops Owl Across Island Populations In the Ryukyu Archipelago and Two Oceanic Islands

Abstract The Ryukyu Scops Owl, Otus elegans, is distributed over a 1,200-km area, only inhabiting islands. Within this range, I studied this species across 20 continental islands in the Ryukyu Archipelago and two oceanic islands. Although most studies recently use quantitative continuous measurements of many specific aspects of the vocalization, I introduced a new method, “typological analysis” to visually classify variation of spectrograms according to the shape of syllable in the owl species, examining their dialects in relation to their geographical distribution. In the typological analysis, hoot, syllable, and element types were defined according to the number of syllables, the degree of timescale overlap of the first and second elements in the second syllable, and relative differences of duration and frequency of two elements in the second syllable, respectively. Although frequencies of hoot and element types in each island population were significantly different between the island groups north and south of the Kerama Gap across the archipelago, hoot and element types were shared between the island groups. Furthermore, typological variation occurred in syllable types, however there were no differences in frequencies of syllable types between the island groups. Geographic structure in vocal parameters as steep clines with stepped variation is represented as a dialect. According to the definition, this study found that no unique dialects in hoots occurred between the different island populations of Ryukyu Scops Owls. The Kerama Gap might act as a biogeographical barrier, contributing to the differentiation between owl hoots according to spectrotemporal analyses; however, the typological analysis detected the distribution of typological characteristics of hoots on the small islands north of the Kerama Gap that contradicts this concept of a biogeographical barrier. Because the typological analysis needs to visually examine each individual by careful attention to detail, it is a good method for discovering minor geographic variations and patterns in bird vocalizations.