The adaptive significance of aggregation behaviour in the dogwhelk Nucella lapillus (L.)

Summary Three kinds of aggregation behaviour were observed in an exposed shore population of Nucella lapillus. Aggregations on the open rock surface during the summer protected dogwhelks from water movement, and were not found on shores where the topography conferred protection. Feeding occurred mainly within these aggregations, probably because individuals experienced less disturbance there than when isolated. Physical contact was important in holding animals together.Winter and pre-breeding aggregations were usually found in clefts or pools. All age groups formed winter aggregations, but those of immature dogwhelks were not as permanent as those of adults, and the latter merged with the prebreeding aggregations. Winter aggregations protected dogwhelks from dislodgment when their ability to regain a foothold was reduced by low temperatures, while pre-breeding aggregations brought the sexes together for fertilization, but the permanence of adult winter aggregations suggested that reproductive activity may have been occurring within them.     

Functional Convergence of Ecosystems: Evidence from Body Mass Distributions of North American Late Miocene Mammal Faunas

There is disagreement among ecologists as to whether ecosystem system behavior in general is the net result of all of the complex internal system interactions (bottom-driven) or if the behavior is driven by a limited number of key processes (top-driven). If ecosystems are primarily bottom-driven in nature, then it is unlikely that any two complex ecosystems will ever behaviorally converge as a simple matter of probability, or that their behaviors will ever be predictable. Conversely, evidence of ecosystem convergence would suggest that the systems are top-driven, with the corollary that their behaviors can be understood (and therefore in principle predicted) without a complete understanding of their internal workings. Research has demonstrated that body mass distributions of terrestrial animals broadly reflect ecosystem function. Thus, comparable but causally disconnected terrestrial ecosystems that demonstrate similar body mass distributions would suggest ecosystem convergence. To look for this possible convergence, I generated body mass distributions in a time series for late Miocene North American mammal faunas from the Gulf Coastal Plains, Great Plains, and Pacific coastal region, and compared them with data from the modern Serengeti savanna region. The data show that during the early late Miocene Gulf Coastal Plain faunas resembled each other but were distinctly different from that of the Serengeti, the Great Plains fauna resembled the Serengeti, while the Pacific Coast fauna showed no resemblance to any of the others. However, during the latest Miocene the Gulf Coastal Plain faunas were transformed so as to strongly resemble the Serengeti fauna. The resemblance with the Serengeti was maintained by the Great Plains faunas until at least the end of the Miocene, while the Pacific Coast faunas remained distinctly different from the others. These findings suggest that the late Miocene ecosystems of the Gulf Coastal Plain and Great Plains regions (but not the Pacific Coast region) converged with that of the Serengeti savanna fauna and thus that these ecosystems were/are top-driven rather than bottom-driven in nature.     

Habitat utilization by sympatric European mink<Emphasis Type="Italic">Mustela lutreola</Emphasis> and polecats<Emphasis Type="Italic">Mustela putorius</Emphasis> in south-western France

The European minkMustela lutreola Linnaeus, 1761 and the European polecatMustela putorius Linnaeus, 1758 are related species sympatric in southwestern France. The European mink is rapidly disappearing whereas the polecat maintains good populations. Seasonal habitat use of both species was compared in the Landes de Gascogne region to identify if some vulnerability factors of the European mink were associated with habitats occupied by this mustelid. Potential habitats were mapped using a satellite picture and 12 main types of habitats were defined. Animal locations were recorded by radiotracking 9 European mink and 14 polecats from March 1996 to August 1999. Resting animals were located by triangulation, and, when possible, resting places were described. Animals in activity were tracked by continuous monitoring. Data collected revealed a strong preference of European mink for flooded habitats, particularly open marshes, flooded woodlands and moorlands. They seldom left the corridor of the riparian forest and their resting places were mainly in flooded environments, above ground (under herbs or bushes) or in cavities between tree roots. European polecats were less tightly linked to wetlands. Most of their locations were in the pine forests outside the valleys and their resting places were mainly in burrows. The strong specialisation of European mink in aquatic habitats is probably one of the main reasons for its decline because wetlands suffer drastic damages throughout all of its range. Maintaining adequate water levels is crucial for satisfying habitat requirements of mink.     

Reproductive tactics of the Asian cichlids of the genusEtroplus in Sri Lanka

Synopsis The Asian cichlids,Etroplus maculatus (the orange chromide) and E. suratensis (the green chromide) in Sri Lanka reproduce twice during the year when water conditions are favorable for nest construction and maintaining visual contact with offspring. These are the drier premonsoonal and monsoonal seasons when water turbidity decreased and salinity increased. When breeding in isolation orange chromide pairs selected dense vegetation where nests were camouflaged. During the peak breeding cycle (July) orange chromide pairs selected sparse vegetation for nesting as a compromise between survival of young and availability of adult food. These areas were also occupied by foraging non-breeding conspecifics which increased the threat of cannibalism of offspring. Under these pressures most orange chromides nested in colonies which helped decrease both actual and attempted cannibalism. The sympatric green chromide does not forage during nesting and nest site selection was determined mainly by factors favoring offspring survival. Biparental care is exhibited by both species. One member of an orange chromide pair stands guard over offspring while the other leaves the territory to forage — their roles are reversed every few minutes. The total parental investment is equivalent to the full investment of a single parent. Monogamy appears to be maintained by their metabolic constraints. In the green chromide both parents are vigilant over offspring and neither forages thus spending twice as much time in parental investment.     

Foraging activity of Rhinolophus hipposideros on the Island of Herrenchiemsee, Upper Bavaria

We studied the foraging behaviour of Rhinolophus hipposideros on the island “Herrenchiemsee” in Lake Chiemsee (Upper Bavaria) during summer 2001. The island offers extensively managed woodlands, highly structured open landscapes and a broad reed belt around the shore. On average the flight activity of the 6 radio tracked females outside the roost lasted 229 min per night. The home range size varied between 6.8 and 62.7 ha (mean 25.2 ha). The size of the activity centres varied between 2.8 and 8.2 ha (mean 5.3) and all except one were located almost exclusively in woodland. Within woodlands the bats did not select for specific spatial structures (different age classes of the stands or canopy densities). Only two bats regularly foraged in additional habitats outside woodlands. One of these bats used orchards and tree rows; the other foraged over artificial ponds and gardens adjoining to its woodland foraging area. We never found the bats foraging over the lake or the reed belt. Longer linear landscape elements as tree lines were used during commuting flights but there was no indication of a continuous foraging activity along these elements. Two females left the island to forage on the mainland in August after the fledging of juveniles. To reach the mainland shore, the bats had to fly at least 1.2 km across the lake.

Assuming that most foraging flights on the island occur in woodlands, a bat density in this habitat type of 0.7 bats/ha can be calculated.     

Endangered but genetically stable—Erythrophleum fordii within Feng Shui woodlands in suburbanized villages

Feng Shui woodlands are naturally or artificially formed green areas in southern China. They are precious for maintaining ecosystem balance in modern semiurban environments. However, they are generally small and geographically isolated from each other, and the status of genetic diversity of the plant species within them has been almost neglected. Therefore, we studied the genetic diversity of the endangered Erythrophleum fordii in eight Feng Shui woodlands (a total of 1,061 individuals) in Guangzhou, a large city in southern China, using microsatellites. For comparison, one population with 33 individuals sampled in a nature reserve was also studied. Although our results indicate that significant demographic declines occurred historically in E. fordii, such declines have not resulted in consistent reductions in genetic variation over generations in Feng Shui populations in the recent past, and the levels of genetic variation in these populations were higher than or comparable to the genetic variation of the population in the nature reserve. In addition, our parentage and paternity analyses indicated widespread and potential long‐distance pollen flow within one Feng Shui woodland, indicating the presence of an unbroken pollination network, which would at least partially alleviate the genetic erosion due to habitat fragmentation and the unequal gene contributions of E. fordii parents to their progenies when favorable recruitment habitats are absent under most of the parent trees. Overall, our results suggest that E. fordii in Feng Shui woodlands may not be driven to extinction in the near future. Nevertheless, uncontrolled fast urban development with a lack of awareness of Feng Shui woodlands will cause the local extinction of E. fordii, which has already happened in some Feng Shui woodlands.     

Influence of plot characteristics and surrounding vegetation on the intra-plot spatial distribution of Empoasca vitis

• 1 Spatial distributions of adults and nymphs of Empoasca vitis were assessed during 3 years inside two adjacent vine plots having considerable intra‐plot variability, diversified natural ground cover and surrounding vegetation, and no insecticide application.
• 2 Geostatistical analysis confirmed that, in spite of repeated adult migrations, spatial distributions of summer populations were highly aggregated, similar every year and similar between adults and nymphs. Comparison of insect distribution with intra‐plot characteristics, such as vine plant vigour (leaf density and leaf chlorophyll concentration) and phenology, plot topography and surrounding vegetation, revealed that E. vitis clearly aggregates in areas with the most vigorous vine plants.
• 3 Even though the presence of natural enemies in the surrounding vegetation was confirmed by specific observations, we did not observe significant population decrease at the contiguous plot edges. Natural ground cover, together with the absence of insecticide, might allow the spreading and perennial conservation of E. vitis natural enemies inside the plots.
• 4 Clear adult aggregations observed along downwind woodlands suggest that this vegetation acts as a barrier and intercepts the adults flying passively across the plot. However, this surrounding vegetation could also serve as an alternative refuge when vine water deficit and vine foliage temperature increase.

     

Linking seasonal distribution patterns with prey availability in a central-place forager, the Steller sea lion

Aim We used a novel approach to infer foraging areas of a central‐place forager, the Steller sea lion (Eumetopias jubatus), by assessing changes in the temporal and spatial distribution patterns of sea lions at terrestrial sites. Specifically, our objectives were (1) to classify seasonal distribution patterns of Steller sea lions and (2) to determine to what extent the seasonal distribution of Steller sea lions is explained by seasonal concentrations of prey. Location Southeast Alaska, USA. Methods Steller sea lions of all age classes were counted monthly (2001–04) by aerial surveys at 28 terrestrial sites. Hierarchical cluster analysis and principal components analysis were used to classify seasonal distribution patterns of Steller sea lions at these terrestrial sites. We estimated the proportion of sea lions in the study area that were associated with each seasonal distribution pattern. Results Multivariate ordination techniques revealed four distinct seasonal distributional patterns. During December, 55% of the sea lions in the study area were found at Type 1 sites, located near over‐wintering herring aggregations. During May, 56% of sea lions were found at Type 2 sites, near aggregations of spring‐spawning forage fish. In July, 78% of sea lions were found at Type 3 sites, near summer migratory corridors of salmon. During September, 44% of sea lions were found at Type 4 sites, near autumn migratory corridors of salmon. Main conclusions Seasonal attendance patterns of sea lions were commonly associated with the seasonal availability of prey species near terrestrial sites and reflected seasonal foraging patterns of Steller sea lions in Southeast Alaska. A reasonable annual foraging strategy for Steller sea lions is to forage on herring (Clupea pallasii) aggregations in winter, spawning aggregations of forage fish in spring, salmon (Oncorhynchus spp.) in summer and autumn, and pollock (Theragra chalcogramma) and Pacific hake (Merluccius productus) throughout the year. The seasonal use of haulouts by sea lions and ultimately haulout‐specific foraging patterns of Steller sea lions depend in part upon seasonally available prey species in each region.     

Food-web structure and ecosystem services: insights from the Serengeti

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year. The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species. Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web. The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web. If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem. The best way to do this is by controlling the external forces that threaten the boundaries of the ecosystem and by balancing the economic services the park provides between local, national and international needs. I conclude by discussing how the ecosystem services provided by the Serengeti are driven by species on different trophic levels. Tourism provides the largest financial revenue to the national economy, but it could be better organized to provide more sustained revenue to the park. Ultimately, ecotourism needs to be developed in ways that take lessons from the structure of the Serengeti food webs, and in ways that provide tangible benefits to people living around the park while also improving the experience of all visitors.     

Notes on paternal care and sibling cannibalism in the giant water bug, Lethocerus deyrolli (Heteroptera: Belostomatidae)

Males of the giant water bug, Lethocerus deyrolli, care for egg masses on vegetation above the water surface. They supply the developing eggs with water and guard them against predators. In the present study, mechanisms by which paternal care is extended were found. Males were found situated just below the water on the natal substrate (usually a stick), and the first instar nymphs were aggregated around the substrate. When disturbed, the males showed aggressive behavior, threatening the intruder with their forelegs. Nymphs up to 12 h old did not attack the offered sibling nymphs or anuran larvae, which are common prey in the field. The 24 h‐old nymphs attacked both prey animals; however, they preferred anuran larvae. Cannibalistic behavior in the nymphs was well developed 72 h after hatching, when the nymphs had already dispersed from the natal substrate. The suppression of sibling cannibalism in younger nymphs would promote the maintenance of tight nymphal aggregations and consequently extend male care in this predatory species.     

Elemental analysis of mineral lick soils from the Serengeti National Park, the Konza Prairie and Yellowstone National Park

We analyzed mineral lick soils and non-mineral lick soils from the Serengeti National Park, the Konza Praine, and Yellowstone National Park The concentrations of 14 different elements considered important for ungulate nutrition were analyzed to determine the relative importance of Na vs other elements in attracting animals to lick areas Only Na was consistently higher in the mineral lick soils of the three ecosystems Mean Na concentrations were c 20x greater in Serengeti licks, 10x greater in Konza licks and 3x greater in Yellowstone licks compared to the respective non-lick soils Despite the numerous elements analyzed for this survey, our results suggest that Na is the primary element initiates mineral lick use in these widely separated ecosystems The widespread distribution of Na-deficient forage likely explains the importance of Na in most mineral licks     

Proximate weather patterns and spring green‐up phenology effect Eurasian beaver (Castor fiber) body mass and reproductive success: the implications of climate change and topography

Low spring temperatures have been found to benefit mobile herbivores by reducing the rate of spring‐flush, whereas high rainfall increases forage availability. Cold winters prove detrimental, by increasing herbivore thermoregulatory burdens. Here we examine the effects of temperature and rainfall variability on a temperate sedentary herbivore, the Eurasian beaver, Castor fiber, in terms of inter‐annual variation in mean body weight and per territory offspring production. Data pertain to 198 individuals, over 11 years, using capture‐mark‐recapture. We use plant growth (tree cores) and fAPAR (a satellite‐derived plant productivity index) to examine potential mechanisms through which weather conditions affect the availability and the seasonal phenology of beaver forage. Juvenile body weights were lighter after colder winters, whereas warmer spring temperatures were associated with lighter adult body weights, mediated by enhanced green‐up phenology rates. Counter‐intuitively, we observed a negative association between rainfall and body weight in juveniles and adults, and also with reproductive success. Alder, Alnus incana, (n = 68) growth rings (principal beaver food in the study area) exhibited a positive relationship with rainfall for trees growing at elevations >2 m above water level, but a negative relationship for trees growing <0.5 m. We deduce that temperature influences beavers at the landscape scale via effects on spring green‐up phenology and winter thermoregulation. Rainfall influences beavers at finer spatial scales through topographical interactions with plant growth, where trees near water level, prone to water logging, producing poorer forage in wetter years. Unlike most other herbivores, beavers are an obligate aquatic species that utilize a restricted ‘central‐place’ foraging range, limiting their ability to take advantage of better forage growth further from water during wetter years. With respect to anthropogenic climate change, interactions between weather variables, plant phenology and topography on forage growth are instructive, and consequently warrant examination when developing conservation management strategies for populations of medium to large herbivores.     

Vertical Distribution of the Far East Trepang Apostichopus japonicusin Vostok Bay,Sea of Japan

The abundance, weight, and age structure of aggregations of the Far East trepang Apostichopus japonicuswere studied in Vostok Bay, Sea of Japan, during the first part of September 2000. The highest density of aggregations (8.3 ± 0.5 ind/m²) and biomass (131.88 ± 10.50 g/m²) of animals was characteristic for coastal sites at the depth 0.5–1.5 m. With anincrease in depth the biomass and density of A. japonicusreduced 1.5 and 3 (depth 5–6 m), 220 and 830 times (depth 8–15 m) respectively. The ratio of large animals concurrently increased in the aggregation structure. The specifics of the distribution and spatial variability of the aggregation structure are discussed in relation to uncontrolled fishing of holothurians of large sizes.     

Selection of feeding areas by cattle in a spatially heterogeneous environment: selection between two tropical grasses differing in accessibility and abiotic environment

A herd of 28–31 Japanese Black (Bos taurus) cows were allowed to graze an experimental plot comprising monoculture swards of centipedegrass (Eremochloa ophiuroides; CG; preferred grass; 0.30 ha) and bahiagrass (Paspalum notatum; BG; less preferred grass; 0.22 ha) for five consecutive days (09:00–16:00 h) in two seasons (summer and autumn), under a substantial travel cost between the two grasses and a trade-off between the forage preference and some abiotic factors. The two swards were apart from each other and connected by an alley of about 80 m. The CG comprised low (CGL) and high (CGH) availability areas (0.15 ha each). The animals grazed mainly the CGH and CGL, which were in the distance and lacked water and shade, in the morning when the air temperature was relatively low. Then, in the afternoon, they shifted the major grazing area to the BG with water, shade, and close proximity to the barn where they camped. On a daily basis, the animals consistently showed preference for the CGH except one case, switching 6–14 times between the BG and CG. The results demonstrate that animals, even when the preferred species is of lower accessibility and in a less favorable abiotic environment, switch between the preferred and less preferred species and eat mixed diets to show a partial preference. They cope with increased travel costs and trade-offs between forage preference and abiotic environment by reducing switching frequency between the species and shifting target species over the course of the day. Further studies are warranted to test how these mechanisms are successful in maintaining the preference under increased distances and trade-offs.     

Structure and specific features of formation of aggregations of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) in the Norwegian Sea pelagial

Results of studies of the structure and specific features of formation of aggregations of deepwater redfish Sebastes mentella in the Norwegian Sea pelagial are provided. Data on the biological characteristics of S. mentella from different regions of the Norwegian Sea pelagial do not allow us to consider its aggregations as separate populations. On the basis of comparative analysis of the structure of aggregations in the Norwegian Sea and of population parameters and specific features of the life cycle of S. mentella in different parts of the Atlantic Ocean, its complex intraspecies organization at sites of overlapping of two largest populations—North Atlantic and Norwegian-Barents Sea-was established. The formation of pelagic aggregations in the water area of the Norwegian Sea occurs due to migration of maturing and mature individuals from the adjoining water areas. In the southern areas of the Norwegian Sea, dominant recruitment comes from the pelagial of the northeastern part of the Irminger Sea, which is promoted by the direction of streams of the North-Atlantic Current; it is not excluded either that fish can migrate to the southern part of the sea from the slopes of the Faeroes, Faeroes-Icelandic threshold, and the western coast of Norway. Migration to the northern areas of the sea is mainly performed by rapidly maturing fish from the rearing region from the western slopes of the Barents Sea and Spitsbergen Archipelago. The presence of seasonal migrations hinders the formation in the pelagial of perch isolated groups and promotes their migration.     

Social, state-dependent and environmental modulation of faecal corticosteroid levels in free-ranging female spotted hyenas.

Little is known about to what extent the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis may be state dependent and vary in the same species between environments. Here we tested whether the faecal corticosteroid concentrations of matrilineal adult female spotted hyenas are influenced by social and reproductive status in adjacent ecosystems and whether they vary between periods with and without social stress. Females in the Serengeti National Park frequently become socially subordinate intruders in other hyena territories by undertaking long-distance foraging trips to migratory herds, whereas in the Ngorongoro Crater they usually forage inside their own small territories on resident prey. The faecal corticosteroid concentrations in Serengeti females were significantly higher than in Ngorongoro females. Energy expenditure by lactation is exceptionally high in spotted hyenas and this may be reflected in their corticosteroid levels. The faecal corticosteroid levels in both populations were higher in lactating than in non-lactating females. During periods of social stability, faecal corticosteroid concentrations increased in non-lactating females but not in lactating females as social status declined. Lactating Serengeti females had significantly higher faecal corticosteroid concentrations during periods with acute severe social stress than during periods without, indicating that the HPA axis is sensitive to social stimuli even in lactating females. So far few studies have used non-invasive monitoring methods for assessing social stress in freeranging animals. This study demonstrates for the first time, to the authors' knowledge, that corticosteroid concentrations may differ between periods with and without social stress for a free-ranging female mammal and that the modulating effect of social status may depend on reproductive status.     

Clothing color mediates lizard responses to humans in a tropical forest

Identifying how ecotourism affects wildlife can lower its environmental impact. Human presence is an inherent component of ecotourism, which can impact animal behavior because animals often perceive humans as predators and, consequently, spend more time on human-directed antipredator behaviors and less on other fitness-relevant activities. We tested whether human clothing color affects water anole (Anolis aquaticus) behavior at a popular ecotourism destination in Costa Rica, testing the hypothesis that animals are more tolerant of humans wearing their sexually selected signaling color. We examined whether clothing resembling the primary signaling color (orange) of water anoles increases number of anole sightings and ease of capture. Research teams mimicked an ecotourism group by searching for anoles wearing one of three shirt treatments: orange, green, or blue. We conducted surveys at three different sites: a primary forest, secondary forest, and abandoned pasture. Wearing orange clothing resulted in more sightings and greater capture rates compared with blue or green. A higher proportion of males were captured when wearing orange whereas sex ratios of captured anoles were more equally proportional in the surveys when observers wore green or blue. We also found that capture success was greater when more people were present during a capture attempt. We demonstrate that colors “displayed” by perceived predators (i.e., humans) alter antipredator behaviors in water anoles. Clothing choice could have unintended impacts on wildlife, and wearing colors resembling the sexually selected signaling color might enhance tolerance toward humans.     

Behavioral and hormonal responses to the availability of forage material in Western lowland gorillas (Gorilla gorilla gorilla)

We investigated how forage material affects indicators of welfare in three male Western lowland gorillas (Gorilla gorilla gorilla) at the Detroit Zoo. In addition to their maintenance diet and enrichment foods, the gorillas generally received forage material four times a week. From this baseline, we systematically manipulated how much forage material the group received on a weekly basis, with either daily or bi (twice)‐weekly presentation of browse (mulberry, Morus sp.) or alfalfa hay. We collected behavioral data (60 hr per gorilla) and measured fecal glucocorticoid metabolites (FGM). Mixed models indicated that the presence of forage material significantly increased time feeding (F_2,351 = 9.58, p < 0.001), and decreased rates of noncontact aggression (F_2,351 = 3.69, p = 0.03), and regurgitation and reingestion (F_2,353 = 4.70, p = 0.01). Regurgitation and reingestion were never observed during the condition when forage material was provided daily. When forage material was provided, time spent feeding was similar across gorillas, compared to a disproportionately greater amount of time spent feeding by the dominant individual when forage material was absent. Providing forage material in addition to the regular diet likely created more opportunities for equitable feeding for the subordinate gorillas. FGM concentrations did not vary based on the presence or type of forage material available and, instead, likely reflected group social dynamics. In general, alfalfa and mulberry had similar impacts on behavior, indicating that alfalfa can be an adequate behavioral substitute during times when browse is less readily available for gorillas housed in seasonally variable climates.     

Flock feeding and food intake in Little Egrets Egretta garzetta and their effects on food provisioning and reproductive success

Food provisioning to chicks of Little Egret Egretta garzetta in a colony at Ligagneau in the Camargue, southern France, was measured using electronic nest balances. Both pair members supplied food to the chicks, and each performed three to five alternating foraging trips. The loading rate during the first trip of the day (1.09 g/min) was more than three times as high as that during later trips (0.32 g/min) and accounted for 20% of the daily amount of food delivered. This food was collected while the birds were feeding in dense aggregations on mosquitofish which had become temporarily concentrated due to hypoxic conditions overnight in the surrounding marsh. Later in the day, when this concentrated food source was no longer available, the birds fed solitarily. The total amount of food delivered per day remained constant at 385 g as chick age increased from 10 to 20 days. Given the observed loading rates, 385 g is near the maximum amount of food the pair can deliver during a 16.5-h daylight period when they forage continuously throughout the day but only one parent at a time. This indicates that a time constraint limits the amount of food delivered to a brood during this stage of the breeding cycle. Given this time constraint, the total amount of food delivered per day would have been reduced by 25% if the birds had not been able to benefit from the concentrations of mosquitofish during the early morning. Breeding success was significantly higher at Ligagneau (3.25 chicks/nest) than in other Camargue colonies (2.69 chicks/nest). In addition, post-fledging survival of chicks with a low rank in the brood hierarchy was probably better at Ligagneau than elsewhere in the Camargue. We attribute this elevated reproductive output at Ligagneau to the exceptionally large amount of food collected by egrets during the early morning aggregations, which were probably formed in response to predictable concentrations of mosquitofish in the permanent marshes surrounding this colony. Such aggregations were rarely observed in the temporary marshes surrounding the other colonies, probably because the occurrence and location of fish concentrations are difficult to predict in this habitat due to rapidly falling water levels.     

Distribution Pattern of Far Eastern Sea Cucumber Apostichopus japonicus in Busse Lagoon (Southern Sakhalin)

We analyzed the distribution pattern and size structure in aggregations of the far eastern sea cucumber (trepang), Apostichopus japonicus in Busse Lagoon (Southern Sakhalin). Trepang populations, which differ in their size composition and population density, have been grouped by their spatial differentiation. It has been shown that in the absence of solid substrates in the lagoon, the animals gather on substrates such as the alga Ahnfeltia tobuchiensis and on clusters of the oyster Crassostrea gigas. It is found that on the southeastern part of the lagoon, trepang makes up an extensive aggregation confined to the bed of Ahnfeltia; the distribution of the holothurians mostly has a random pattern. In the northwestern part of the lagoon, trepang makes up aggregations on oyster and algal beds; the distribution of these aggregations shows a random pattern.