ORNITHOLOGICAL Science

Volume 1 Number 1 January 2002


Loyn RH
Patterns of ecological segregation among forest and woodland birds in south-eastern Australia.

Much information has been gathered on birds of eucalypt forests and woodlands in south-eastern Australia. This was examined to assess some of the mechanisms of ecological segregation that may apply. A database was constructed of 209 species pairs (148 species from 48 genera). Most patterns resemble those reported overseas, with habitat and range featuring as major segregating mechanisms. Use of different strata and substrates was the dominant primary mechanism allowing use of identical space by congeners. Mechanisms such as specific food preferences, migration and choice of nest sites contributed but rarely as primary factors. One species pair appears to show no ecological segregation, despite co-existence in varying proportions over a large geographical range. Indiscriminate interspecific aggression is used by some species to maintain high levels of resources for themselves, in environments that can sustain such resources throughout the year. Communal breeding is a feature of those species. Implications for conservation are discussed.

Recher HF, Davis WE Jr & Calver MC
Comparative foraging ecology of five species of ground-pouncing birds in western Australian woodlands with comments on species decline.

In this paper, we compare the foraging ecology of five Australian robins (Petroica multicolor, P. goodenovi, Eopsaltria griseogularis, Microeca fascinans, and Melanodryas cucullata) in woodlands of Western Australia. Australian robins are insectivorous and obtain the greatest proportion of their prey by pouncing from a perch to the ground. Data were collected at three different sites in eucalypt (Eucalyptus) woodland and two sites in acacia (Acacia) woodland. The species differed in habitat, structure of the ground substrates where prey were taken, proportion of foraging manoeuvres used, height of foraging perches and prey-attack distances, though there were broad overlaps in all foraging dimensions. Within a site, species were more similar to each other in their foraging behaviour and selection of foraging substrates than they were to conspecific individuals occurring elsewhere. This indicates that potential foraging behaviours were very broad, and their expression is determined by the characteristics of the habitat and available prey. At all sites, robins took prey from ground substrates characterised by a mosaic of bare soil, low ground vegetation, and litter. The smallest species, P. goodenovi, used lower perches than the other robins and probably searched for small prey which it located at short distances. P. goodenovi had the widest distribution and was the most abundant of the species studied. The implications of these findings for the conservation of ground-foraging birds in Australia are discussed.

Moenkkoenen M & Forsman JT
Heterospecific attraction among forest birds: a review.

In this paper we review the evidence for a habitat selection process where colonizing individuals use other species presence as cues to profitable breeding sites. Our experimental studies in Fennoscandia and North America have shown that density and species richness of migrant birds breeding in the forests respond positively to experimentally augmented titmice densities. We used analytical modeling to analyze ecological conditions, which may favor a habitat selection process where later arriving individuals (colonists) use the presence of earlier established species (residents) as a cue to profitable breeding sites. We compared the fitness of two colonist strategies: colonists could either directly sample the relative quality of the patches (termed samplers) or, alternatively, they could also use residents as a cue of patch quality (cue-users). Model results suggested that cue-using strategy is more beneficial in most ecological conditions and that this may result in heterospecific attraction. Further field experiments showed that migrant individuals selected nest sites at close vicinity of nesting titmice, and bred earlier and reproduced better. We conclude that heterospecific attraction may be a common and widespread process among forest birds particularly in seasonal environments.

Seki S & Sato T
The effect of a typhoon on the flocking and foraging behavior of tits.

A typhoon, that struck Kyushu, the southernmost of the four main islands of Japan, in September 1999, causing extensive wind damage to forests, was found to have affected the flocking and foraging behavior of Varied Parus varius and Great Tits P. major. After the typhoon had passed, the tits tended to participate in mixed-species flocks and preferred to forage in the lower parts, rather than in the upper parts, of the trees. Also the proportion of plant products in the diet of the Varied Tit was reduced. The population and average flock size of the tits, however, remained stable even after the typhoon. The abundance of plant products as food resources remained unchanged despite severe damage to the trees, but the vegetation cover was reduced, which probably increased the predation risk. The increase of mixed-species flocking may have resulted from the increased risk of predation; mixed-species flocking is thought to increase vigilance and foraging efficiency while not increasing intraspecific competition. Changes in diet and preferred foraging sites were also consistent with the increased predation risk hypothesis. We conclude that the changes in foraging and flocking behavior after the typhoon were mainly due to the increased predation risk caused by the reduced vegetation cover.

Murakami M
Foraging mode shifts of four insectivorous bird species under temporally varying resource distribution in a Japanese deciduous forest.

Temporal changes in the foraging habitat of four forest bird species and the distribution pattern of arthropod populations were investigated. The abundance and distribution of arthropods changed drastically with the season within the forest. Lepidoptera larvae were most abundant in the canopy in the first three weeks after budbreak; their numbers decreased rapidly during mid-June. In contrast, on the forest floor, the larvae were abundant from early to late June. The foraging height of the Narcissus Flycatcher Ficedula narcissina changed in parallel with the distribution pattern of Lepidoptera larvae. Three other species, the Great Tit Parus major, Marsh Tit P. palustris, and Eastern Crowned Warbler Phylloscopus coronatus, however, did not change their foraging heights; they continued to forage in the canopy. These differences are probably due to the greater preference of the flycatcher for Lepidoptera larvae compared with the other three species. The three other species switched from feeding on Lepidoptera larvae to spiders or other arthropods in mid June, when the number of Lepidoptera larvae decreased in the canopy. The results of this study suggest that the abundance and distribution of arthropods and differences in foraging tactics among bird species considerably affect avian foraging habitat. The foraging behavior of three species of forest birds revealed species-specific responses to spatio-temporal fluctuations in the distribution of resources.

Mizutani M & Hijii N
The effects of arthropod abundance and size on the nestling diet of two Parus species.

Feeding habits of Parus major and P. varius inhabiting coniferous plantations of Cryptomeria japonica and Larix kaempferi, each containing a small area of deciduous broad-leaved trees, were analyzed in relation to the abundance and size distribution of arthropods. In a C. japonica-dominated (CJ) area, C. japonica trees were mainly used by P. major only, while deciduous broad-leaved trees were used by both Parus species. In a L. kaempferi-dominated (LK) area, both Parus species used L. kaempferi trees and deciduous broad-leaved trees. The composition of nestling diets differed between Parus species. For prey size, the difference in the breadth was smaller and the overlap was larger between areas than between species. These results suggest that each Parus species preferred a specific size class of prey. That is, the single-prey loader P. major preferred large prey, whereas the multiple-prey loader P. varius preferred small prey. The abundance and size distribution of arthropods greatly differed among foraging microhabitats. Both Parus species selectively used foraging microhabitats according to their prey-size preference.

Hino T, Unno A & Nakano S
Prey distribution and foraging preference for tits.

We examined the abundance and distribution of prey in four different height strata and eight tree species in a temperate forest, and analyzed the influence on foraging preference by three breeding tit (Parus) species. Densities of arthropod prey for tits in canopy foliage varied with tree species but not with height. Most of them were Lepidoptera larvae. Also, interspecific differences in choice of foraging substrate were found between tree species but not in height. These results demonstrate that tree species composition is a more important habitat factor than foliage height profile for coexistence of different tit species in forests. We examined four different measures of prey abundance to find how tits chose tree species. The largest species, the Great Tit P. major, preferred the tree species with high total biomass, and the intermediate-sized Willow Tit P. montanus preferred those with high density per leaf area. Concentrated searching for prey on a few tree species with high total biomass may be a useful strategy for inflexible perch-gleaners such as P. major, and finer-scale searching on each leaf may be more practical for agile foragers such as P. montanus which often hang-glean to reach less accessible food. In spite of these differences, both species gained benefits from choosing the tree species on which they foraged most efficiently. In contrast, the smallest species, the Coal Tit P. ater, frequently foraged on food-poor tree species. Of the three tit species, P. ater was the most generalized forager, using diverse techniques on a variety of tree species and specializing at capturing small prey quickly. These foraging patterns may make it possible for the smallest species to coexist with the other tit species.

Sodhi NS
The effects of food-supply on Southeast Asian forest birds.

Southeast Asian forests are being lost at an alarming rate. This unprecedented deforestation is resulting in avifauna losses. Despite this, Southeast Asian avifauna remains poorly studied. A few studies measured the food-supply and correlated it with the Southeast Asian forest bird ecology. These correlative studies (qualitative as well as quantitative) show that food-supply can affect the bird diversity, abundance/density, breeding ecology, body condition, ranging behaviour and/or flocking behaviour. However, there has been no experimental study conducted to determine the effects of food-supply on the forest bird ecology. In this geographic area, exciting research avenues remain available to study the avian feeding ecology and to explore a relationship between food-supply and forest bird ecology. Descriptive, correlative as well as experimental data on these aspects are required to enhance the knowledge of avian ecology as well as for avian conservation purposes.

Yamagishi S, Asai S, Eguchi K & Wada M
Spotted-throat individuals of the Rufous Vanga Schetba rufa are yearling males and presumably sterile.

The Rufous Vanga Schetba rufa is endemic to Madagascar and lives in one-female groups. During the 19941999 breeding seasons, a total of 294 nestlings were banded. Among these nestlings, 51 stayed within the study area as spotted-throat individuals. In the next breeding seasons, 35 of 45 spotted-throat individuals were subsequently observed as black-throated males, and once they became black-throated males, these individuals never reverted to the previous spotted-throat pattern. In contrast, 30 banded nestlings were recovered as yearling females with white throats, and the females color pattern never changed thereafter. All the spotted-throat males were helpers or floaters. All the males of one group consisting of an adult male with a black throat and two males with spotted throats were captured and sacrificed humanely. The testes were dissected from each specimen and were histologically examined. The testes of the spotted-throat males contained only spermatogonia, and no spermatids or spermatozoa were present. In contrast, the testes of the black-throated male were well-developed and contained enlarged seminiferous tubules with lumen, where numerous spermatozoa were evident. Considering these facts, spotted-throat males of this species are assumed to be sterile. We suggest that, due to their underdeveloped testes, the spotted-throat males (one-year-old males) of the Rufous Vanga are physically incapable of breeding.

Amano HE & Eguchi K
Nest-site selection of the Red-billed Leiothrix and Japanese Bush Warbler in Japan.

The Red-billed Leiothrix Leiothrix lutea has been introduced from China and is rapidly increasing in deciduous broad-leaved forests of Japan. We studied nest-site characteristics and nest-site selection of this species and the Japanese Bush Warbler Cettia diphone, a sympatric native species, in southwestern Japan. Both species placed nests exclusively in bamboo thickets and on bamboo stalks. The Red-billed Leiothrix built pendulous nests in the canopy of high concealment. The Japanese Bush Warbler placed nests on the crossing of bamboo stems and selected places of high stem density. The Japanese Bush Warblers placed nests in denser vegetation than the Red-billed Leiothrix. The segregation of nesting microhabitat was also evident in both species to coexist in bamboo thickets. Existence of few inhabitants in bamboo thickets may contribute to the invasion success of the Red-billed Leiothrix.