Egret Colonies Research Articles

Autumn migration routes and wintering areas of juvenile Chinese Egrets (Egretta eulophotes) revealed by GPS tracking

BackgroundThe vulnerable Chinese Egret (Egretta eulophotes) is a long-distance migratory waterbird whose migration and wintering information is poorly understood. This study aims to identify the autumn migration routes and wintering areas of juvenile Chinese Egrets and determine the migration movement traits of this species.MethodsThirty-nine juvenile Chinese Egrets from the Fantuozi Island, an uninhabited offshore island with a large breeding colony of Chinese Egrets in Dalian, China, were tracked using GPS/GSM transmitters. Some feathers from each tracked juvenile were collected for molecular identification of sex in the laboratory. The GPS locations, recorded at 2-h intervals from August 2018 to May 2020, were used for the analyses.ResultsOf the 39 tracked juveniles, 30 individuals began their migration between September and November, and 13 successfully completed their autumn migration between October and November. The juveniles migrated southward via three migration routes, coastal, oceanic and inland, mainly during the night. The migration duration, migration distance, flight speed, and stopover duration of the 13 juvenile egrets that completed migration averaged 5.08 ± 1.04 days, 3928.18 ± 414.27 km, 57.27 ± 5.73 km/h, and 23.08 ± 19.28 h, respectively. These juveniles wintered in the coastal wetlands of Southeast Asia including those in the Philippines, Vietnam, and Malaysia, and only one successfully began its spring migration in June 2020.ConclusionsThis study newly finds that the oceanic route taken by juvenile Chinese Egrets, suggesting that the juveniles are able to fly over the Pacific Ocean without a stopover. Moreover, our novel data indicate that coastal wetlands along the East Asian–Australasian Flyway are important areas for both autumn migration stopover and the wintering of these juveniles, suggesting that international cooperation is important to conserve the vulnerable Chinese Egret and the wetland habitats on which it depends.

Three-dimensional niche partitioning between two colonially nesting ardeid species in central China

BackgroundInterspecific competition is known to be strongest between those species that are both closely related and sympatric. Egrets are colonially nesting wetland birds that often overlap and can therefore be expected to compete in roosting and nesting habitat as well as in diet. According to the niche partitioning hypothesis, it is to be expected that these similar species would show differentiation in at least one of the main niche dimensions to reduce competition. We tested niche partitioning between the colonially nesting Little Egret (Egretta garzetta) and Cattle Egret (Bubulcus ibis) in temporal, spatial and trophic dimensions.MethodsField study was conducted in three mixed egret colonies in Yangxian County, southwest Shaanxi Province, central China. For each nest colony we recorded its spatial location, the height of nesting trees and of nests, the height of roosting trees and of roosting individuals within the trees. We determined the first egg-laying and first hatching dates of the two species. Craw dissection of storm-killed egret nestlings was used to measure the diet. Six transects were surveyed to study foraging habitat selection.ResultsWe found that hatching time of Little Egrets peaked earlier (by about 1 month) than that of Cattle Egrets. Cattle Egrets nested and roosted higher than Little Egrets. The foraging habitats used by Little Egrets were dominated by river banks (73.49%), followed by paddy fields (13.25%) and reservoirs (10.84%), whereas Cattle Egret foraging sites were characterized by grasslands (44.44%), paddy fields (33.33%) and river banks (22.22%). Little Egrets consumed more fishes (65.66%) and Odonata larvae (13.69%) than Cattle Egrets, while Cattle Egrets were found feeding mainly on Coleoptera (29.69%) and Orthoptera (23.29%). Little Egrets preyed on larger mean biomasses of food items than Cattle Egrets.ConclusionsOur results confirm the niche partitioning hypothesis as a mechanism for coexistence among ecologically similar species. In two coexisting egret species, niche partitioning is multidimensional, such that the two coexistent species occupy differing ecological space based on all three temporal, spatial and trophic niche dimensions.

Site Fidelity in Lineages of Mixed–Species Heron Colonies

As heron and egret colonies are sometimes abandoned due to human activity and subsequently newly established at nearby locations, colony locations per se cannot represent colony fates. Here, “colony lineages” were traced by connecting short-distance location shifts between colony sites in consecutive years to quantify the site fidelity of heron colonies themselves rather than the breeding-site fidelity of individuals. Site fidelity of 61 colony lineages recorded from 1963 to 2013 in and around Ibaraki Prefecture, Japan, was evaluated by persistence periods with survival analysis and shapes of historical trajectories by applying the correlated random walk analysis. While 36% (n = 22) of colony lineages did not show site fidelity and lasted only 1 year or indicated untangled shapes of historical trajectories, 64% (n = 39) of colony lineages exhibited site fidelity by reusing the same locations for multiple years or by staying within a small area with entangled shapes of historical trajectories. Even though suitable breeding sites were abundant in the study area and site fidelity of colony members was low, a high rate of site fidelity in colony lineages may be achieved when a few faithful pioneer herons and egrets are followed by many others.

Colonies of Reddish Egret (Egretta rufescens) in Western Mexico

Very little is known about the numbers and distribution of the Reddish Egret (Egretta rufescens) in western Mexico. To estimate the size and distribution of Reddish Egret colonies along the coast of western Mexico, historical and potential Reddish Egret nesting sites were surveyed in 2008 and 2009. Forty-six colonies were found from Baja California to Chiapas. Mean colony size was 24 pairs/colony (95% CI ± 15; n = 46), but most (74%) colonies were < 20 pairs (Median = 7 pairs; n = 46). The largest colony (258 pairs) and the only two colonies with dark and white morphs were found in Oaxaca. The second largest colony (248 pairs) was found in Baja California Sur. The total breeding population was estimated at 1,108 breeding pairs; 788 pairs in 43 colonies were located in northwestern Mexico (Baja California peninsula, Sonora and Sinaloa, subspecies E. r. dickeyi) and 320 pairs in three colonies were in southern Mexico (Oaxaca and Chiapas, subspecies undetermined). This breeding population, although small, is three to four times larger than previously reported for the Pacific Coast of Mexico (225-300 pairs). Thirty-five (76%) Reddish Egret nesting sites were inside a natural protected area; however, the Oaxaca and Chiapas colonies were not.

Phyto- and Zooplankton of Open Overgrown Shallows of the Rybinsk Reservoir Adjacent to a Mixed Grey Heron–Great Egret (Ardea cinerea L. and A. alba L.) Colony at a High Water Level

Phyto- and zooplankton communities developing in the open overgrown shallows of the Rybinsk Reservoir under the influence of a bird colony are shown to lose specific traits of quantitative characteristics and structure fluctuation in response to the elevated water level in contrast to previous findings. Possible reasons, such as the decomposition of sunken coastal vegetation playing the main role, accompanied by the development of semiaquatic macrophytes and trophic relations between algae and invertebrates, are discussed. It is found that increased atmospheric precipitation leads to an increased abundance of Copepoda in the zooplankton. Presumably, this effect correlates with more rapid and intensive inflow of avian vitality products rich in nitrogen into the water, resulting in a change in the stoichiometric ratio of nitrogen and phosphorus in zooplankton food objects to values favorable for copepods.

Development of a Survey Protocol for Monitoring Reddish Egrets (Egretta rufescens) in Florida, USA

Abstract The Reddish Egret (Egretta rufescens) is North America's rarest heron, and roughly 10% of its population resides in Florida. Its dark plumage, subcanopy nesting, and rarity make it difficult to count with aerial surveys, and assessments of ground- and boat-based methods for estimating the abundance of nesting pairs at breeding sites in Florida are lacking. The efficacy of flight-line surveys (boat-based counts of adults flying to and from colonies) and direct counts (ground- or boat-based counts of nests) were compared using data collected by multiple observers during repeated visits to 16 Reddish Egret colonies in three core breeding areas in the State of Florida, USA. Detection rates on direct counts were 77% for a single observer and 89% for two observers combined. Variance between repeated flight-line surveys was high (61%) for 1-hr surveys but substantially lower for 2-hr (18%) and 3-hr (14%) surveys. Estimated nest counts from flight-line surveys were substantially greater than those produc...

Use of noninvasive 'bug-eggs' to enable comparative inferences on genetic mating system with and without parental information: A study in a cattle egret colony.

Colonial waterbirds such as herons, egrets and spoonbills exhibit ecological characteristics that could have promoted the evolution of conspecific brood parasitism and extra-pair copulation. However, an adequate characterization of the genetic mating systems of this avian group has been hindered by the lack of samples of elusive candidate parents which precluded conducting conventional parentage allocation tests. Here, we investigate the genetic mating system of the invasive cattle egret using hematophagous insects contained in fake eggs to collect blood from incubating adults in a wild breeding colony. We tested a protocol with a previously unused Neotropical Triatominae, Panstrongylus megistus, obtained blood samples from males and females in 31 nests built on trees, drew blood from 89 nestlings at those nests, and genotyped all samples at 14 microsatellite loci, including six new species-specific loci. We comparatively addressed the performance of parentage allocation versus kinship classification of nestlings to infer the genetic mating system of cattle egrets. In line with previous behavioral observations, we found evidence in support of a non-monogamous genetic mating system, including extra-pair paternity (EPP) and conspecific brood parasitism (CBP). Parentage allocation tests detected a higher percentage of nests with alternative reproductive tactics (EPP: 61.7%; CBP: 64.5%) than the kinship classification method (EPP: 50.0%; CBP: 43.3%). Overall, these results indicate that rates of alternative reproductive tactics inferred in the absence of parental genetic information could be underestimated and should be interpreted with caution. This study highlights the importance of incorporating samples from candidate parents to adequately determine the genetic mating system of a species. We expand knowledge on the reproductive tactics of colonial waterbirds, contributing novel data on the genetic mating system of the cattle egret, valuable for the design of management strategies for this invasive bird.

Use of noninvasive 'bug-eggs' to enable comparative inferences on genetic mating system with and without parental information: a study in a cattle egret colony

Use of noninvasive 'bug-eggs' to enable comparative inferences on genetic mating system with and without parental information: a study in a cattle egret colony

Extrapolation of random forest models shows scale adaptation in egret colony site selection against landscape complexity

Availability of certain habitats or landscape configurations can cause differential habitat selection in animal species. Landscape complexity can affect foraging scales, home ranges and movement, but its effect on habitat selection is not well documented. We aimed to examine differences in colony site selection of herons and egrets in different regions. We studied whether landscape complexities could affect their scale of selection and habitat preferences. We used colony distribution data and land-use maps for two neighboring regions, Ibaraki and Chiba prefectures in Japan, to create random forest models for analyzing habitat preferences and important scales of selection. We did cross-validation of the models, adjusted for its respective region's land-use maps with changing scales. The scales that best explained colony distribution were 1-, 4-, 10- and 15-km in the Ibaraki region, and 1- and 10-km in the Chiba region. Evergreen forest was the most important variable for Ibaraki at 4-km and for the Chiba at 1-km. The importance of other variables differed for other models. Cross-validation showed that herons and egrets had the same habitat preferences at a 4-km scale in Ibaraki and at a 1-km scale in Chiba. The scale of selection was reduced in Chiba, where the main foraging resources for herons and egrets was more complex. Differences in landscape complexities did not affect habitat preferences but resulted in differences in the scale of selection. Habitat selection models created at the landscape level can be useful to study behavioral aspects difficult to describe with direct observation in detail.

Keratin subsidies promote feather decomposition via an increase in keratin-consuming arthropods and microorganisms in bird breeding colonies

Resource subsidies are well known to increase population densities of consumers. The decomposition process of these subsidised resources can be influenced by increasing consumer abundance. However, few studies have assessed whether resource subsidies can promote resource decomposition via a population increase in consumers. Here, we examined the effects of keratin subsidies on feather decomposition in egret and heron breeding colonies. Egrets and herons (Ardeidae) frequently breed in inland forests and provide large amounts of keratin materials to the forest floor in the form of feathers of chicks (that die). We compared the decrease in the weights of egret and heron feathers (experimentally placed on the forest floor) over a 12-month period among egret/heron breeding colonies (five sites) and areas outside of colonies (five sites) in central Japan. Of the feathers placed experimentally on forest floors, 92-97 % and 99-100 % in colonies and 47-50 % and 71-90 % in non-colony areas were decomposed after 4 and 12 months, respectively. Then, decomposition rates of feathers were faster in colonies than in areas outside of colonies, suggesting that keratin subsidies can promote feather decomposition in colonies. Field observations and laboratory experiments indicated that keratin-feeding arthropods and keratinophilic fungi played important roles in feather decomposition. Therefore, scavenging arthropods and keratinophilic fungi, which dramatically increased in egret and heron breeding colonies, could accelerate the decomposition of feathers supplied to the forest floor of colonies.

Population Dynamics of a Colony of Little Egrets Egretta garzetta at an Estuary in Northern Spain

The population of little egrets Egretta garzetta in Spain is over 20,000 adult breeding birds, making it one of the largest in Europe. Apart from its population size and population trends, the parameters associated with the dynamics (e.g., survival) of the species in Spain are virtually unknown. Our aims were to develop models to assess (1) the colony growth rate, and (2) apparent survival rate of a colony of little egrets breeding in northern Iberia. We used capture-recapture data of little egrets ringed as chicks within the colony, of normally < 30 adult breeding pairs, over a 14-year period starting in 1999. Colony size was observed to be increasing in a linear tendency broken by specific catastrophic events: a very strong hailstorm in 2004 and a pair of peregrines Falco peregrinus that killed several adults in 2005. By 2012, the colony had still not reached the size that it was before the decrease, so it can be concluded that sporadic catastrophic events can have a significant effect on colony size and subsequently population size, especially in small colonies. Annual apparent survival (±SE) was constant and differed between age classes (first-years: 0.15 ± 0.05; adults: 0.78 ± 0.06). Our survival estimate was relatively high compared with other little egret populations, especially for adults. This result, however, may not necessarily apply to other colonies given our small sample size and the lack of data on other factors that also affect the dynamics of the study population.

Serological evidence of H7, H5 and H9 avian influenza virus co-infection among herons in a city park in Jiangxi, China.

Extensive surveillance of influenza A viruses in different avian species is critical for understanding its transmission. Here, a breeding colony of Little Egrets and Black-crowned Night Herons was monitored both serologically and virologically in a city park of Jiangxi in 2009. A portion of herons had antibodies against H7 (52%), H5 (55%) and H9 (6%) subtype avian influenza virus (AIV) in egg yolk samples, and 45% had antibodies against different AIV serotypes (H5, H7 or H9) simultaneously. Greater numbers of samples with anti-AIV H5N1 recombination-4 (Re-4, clade 7) antibodies were measured compared with those containing anti-H5N1 Re-1 (clade 0) and Re-5 (clade 2.3.4) antibodies. Eight strains of H5 and 9 strains of H9 were isolated from poultry of nearby markets. These results indicate wild birds are at risk from infection and co-infection with H7, H5, and H9 subtypes. Investigation of wild bird infection might provide an early warning sign of potential novel AIVs circulating in the nearby poultry industry and even in human society.

Using Scale, Cover Type and GIS to Evaluate Nuisance Cattle Egret Colony Site Selection

The establishment of large Cattle Egret (Bubulcus ibis) breeding colonies in upland residential areas of east central Texas has been observed since the early 1960s. To help understand why Cattle Egrets choose residential breeding sites and predict where these might occur in the future, the geographic extent and scale-dependent nature of the phenomenon was investigated. In east Texas and along the Texas Gulf Coast, Cattle Egret colonies were found in flooded forests or on islands. However, in east central Texas, colonies were often located in upland areas. A habitat suitability model was constructed at multiple scales, outlining land use classes thought to influence upland colony site selection: water, forest and development/residential. The model classified 79% of upland colony locations in high or very highly suitable habitat and 7% in low or very low suitable habitat. The distribution of classes was significantly different than expected considering the distribution of land cover suitability classes across the entire study area (p = 0.036). Cattle Egrets likely choose upland, residential sites to breed when suitable wetland habitats are limited. When flooded tree and shrub or island habitats are absent, egrets may choose the edges of development for breeding sites to limit potential disturbance from ground predators.

Factors Affecting Colony Size and Reproductive Success of Little EgretEgretta garzettain the Sfax Salina, Tunisia

The relationship between breeding site characteristics and breeding parameters of Little Egrets were investigated in the Sfax salt marshes (salina), Tunisia. Thirty colonies distributed among 14 breeding sites were monitored weekly during four breeding seasons (2004–2007). The number of breeding pairs varied among years in parallel with the number of detected colonies. Regressions were used to assess whether breeding site surface area, vegetation cover and inaccessibility to terrestrial predators affected the size and reproductive success of the colonies. Colony size was positively related to breeding site surface area and vegetation cover, while site isolation was the most important predictor of chick productivity. The results suggest that Little Egret colony size in the Sfax salina is determined by availability of nesting places, while chick productivity is controlled by accessibility of breeding sites to terrestrial predators, i.e. dogs. Given these results, an effective management action to conserve Little Egrets in Sfax would be to strategically place fences to protect large and densely-vegetated islets from these predators.

SALMONELLA ENTERICA SUBSP. ENTERICA IN CATTLE EGRET (BUBULCUS IBIS) CHICKS FROM CENTRAL TEXAS: PREVALENCE, SEROTYPES, PATHOGENICITY, AND EPIZOOTIC POTENTIAL

Cattle Egrets have a worldwide distribution, feed in proximity to cattle and other domestic animals, and often nest in large colonies in urban woodlots. Over a 3-yr period, nestlings from five Cattle Egret colonies from Central Texas, USA, were surveyed for salmonellosis. Prevalence of infection ranged from 29% to 95%. Seventeen Salmonella enterica subsp. enterica serotypes were isolated, of which the 4,5,12:i-monophasic serotype predominated in cultures of both the digestive tract and pooled spleen and liver. Of 11 4,5,12:i-monophasic isolates phage typed, eight were determinate type 193. The 4,5,12:i-monophasic isolates were susceptible to all antibiotics tested and were highly invasive in the day-old chick infection model. Microscopic lesions were found in the livers of Cattle Egrets with systemic infections with the 4,5,12:i-monophasic serotype, suggesting that infections with this serotype may often be fatal. Twenty-nine serotypes were identified in 179 S. enterica subsp. enterica isolates from horses admitted to the Texas A&M University Veterinary Teaching Hospital in 2 yr following the Cattle Egret study. The 4,5,12:i-monophasic serotype was not isolated from horses, but 12 serotypes were isolated from both horses and Cattle Egrets. The temporal distribution of the horse cases suggested that Cattle Egrets and horses may be exposed to similar sources of Salmonella, but provided no evidence of transmission between these two species. Similar conclusions were drawn when Cattle Egret isolates were compared to isolates from feedlot and dairy cattle from Texas and surrounding states. Given that the Cattle Egret 4,5,12:i-monophasic serotype was highly invasive and other isolates of this serotype have been associated with food poisoning, it is likely that Cattle Egret colonies pose a health risk to humans living near them.

Bias in aerial estimates of the number of nests in White Ibis and Great Egret colonies

Estimating detection error, as well as the magnitude of other potential survey biases, is essential when sampling efforts play a role in the estimation of population size and management of wildlife populations. We quantified visual biases in aerial surveys of nesting wading birds (Ciconiiformes) in colonies in the Florida Everglades using a negative binomial count regression model to compare numbers of nests in quadrats counted on the ground with numbers estimated from aerial photographs of the same quadrats. The model also allowed the determination of degree of difference between monitoring results based upon such factors as nest density, vegetative cover, and nest turnover rates. Aerial surveys of White Ibis (Eudocimus albus) colonies underestimated the true number of nests found during ground counts by 11.1%, and underestimates were significantly greater (P= 0.047) in a colony with high nest turnover. Error rates did not differ for quadrats that varied in the density of White Ibis nests did not differ, and visual bias did not increase with vegetative complexity (P= 0.73). Estimates of nest density in colonies of Great Egrets (Ardea alba) based on aerial surveys were higher than ground counts for 38% of the quadrats sampled, and mean visual bias was 23.1%. Species misidentification likely contributed to visibility bias for Great Egrets in our study, with some Snowy Egrets almost certainly mistaken for Great Egrets in aerial photos. Biases of the magnitude we observed fro Great Egrets and White Ibises can mask true population trends in long-term monitoring and, therefore, we recommend that detection probability be explicitly evaluated when conducting aerial surveys of nesting birds. SINOPSIS Es esencial poder estimar el error de deteccion, asi como la magnitud de otros tipos de errores al realizar muestreos cuando estos son usados para estimar el tamano poblacional y manejar las poblaciones. Cuantificamos los errores de observacion en las muestras tomadas desde el aire de aves Ciconiiformes en colonias en los Everglades de Florida, usando un modelo de regresion binomial negativo de conteo para comparar los numeros de nidos en cuadrantes contadas desde la tierra con los numeros de nidos estimados usando fotografias aereas de los mismos cuadrantes. El modelo tambien permitio la determinacion del grado de diferencia entre los resultados del monitoreo basado en factores como la densidad de los nidos, cobertura de la vegetacion y la tasa de renovacion de nidos. Los muestreos aereos subestimaron el verdadero numero de nidos en colonias de Eudocimus albus (encontradas durante conteos hechas en la tierra) por el 11.1% y estas subestimaciones fueron significativamente mas grandes (P= 0.047) en una colonia con una alta tasa de renovacion de nidos. Las tasas de error no variaron entre los cuadrantes cuales tenian diferentes densidades de nidos de E. albus y el error asociado con la observacion visual no incremento con la complejidad de la vegetacion (P= 0.73). Las estimaciones de la densidad de nidos en las colonias de Ardea alba basadas en muestreos aereos fueron mas altas que los conteos hechos en tierra para 38% de los cuadrantes muestreados; el error promedio de la observacion visual fue 23.1%. La mal identificacion de las especies probablemente contribuyo al error hecho durante observaciones visuales de A. alba en nuestro estudio, con algunos individuos de Egretta thula posiblemente identificados como A. alba en las fotografias aereas. A largo plazo, los errores del tamano que observamos en el monitoreo pueden enmascarar los patrones verdaderos de patrones poblacionales y por eso recomendamos que la probabilidad de deteccion sea explicitamente evaluado al tomar muestras aereas de aves que nidifican en colonias.

Landscape influence on the quality of heron and egret colony sites

We evaluated landscape associations related to heron and egret colony site selection and the productivity of successful great blue heron (Ardea herodias) and great egret (Ardea alba) nests. The study was based on annual observations (1991–2005) at 45 colony sites known to be active within 10 km of historic tidal marshes of northern San Francisco Bay. The analyses focused on a priori models analyzed within 1, 3, 5, 7, and 10 km of colony sites, using the areal extents of several NOAA land cover types (Landsat images, 2000–2002), number of wetland patches, and total wetland edge as predictor variables. A comparison of landscape characteristics surrounding colony sites with those surrounding randomly selected, unoccupied sites revealed the primary importance of estuarine emergent wetland and open water within 1 km of colony sites. Increased productivity in successful great blue heron nests was associated with more estuarine emergent wetland, open water, and low-intensity development, and less grassland, but was not differentially related to the extent of habitat available within any particular distance from colony sites. The productivity in successful great egret nests was associated with variation in habitat extent at larger spatial scales, especially within 10 km of heronies, with nests producing more young at sites surrounded by more estuarine emergent wetland and low-intensity development, less open water and palustrine emergent wetland, and more patches of wetland habitat. To estimate landscape foraging patterns, we used aircraft to track the flights of great egrets departing from heronries and used the observed flight distances, colony sizes, and the regional distribution of wetland habitat to model regional foraging densities. Results suggested that increasing the extent of wetland feeding areas for herons and egrets might improve reproductive performance in colony sites up to 10 km away, increase foraging by herons and egrets in created or restored wetlands within 3–10 km of sites, and enhance nest abundance at colony sites within 1 km of restoration sites. Regional maps based on the distribution of colony-sites and predictions of landscape influences on colony site selection, nest productivity, and foraging dispersion, suggested areas potentially suitable for colonization.

Argasid Ticks as Possible Vectors of West Nile Virus in Israel

Mites and soft ticks collected directly from wild and domestic birds and their nests were tested for the presence of West Nile virus (WNV). The cattle egret argas, Argas arboreus, was collected from the nests of seven cattle egret colonies. Out of 1,000 A. arboreus pools examined, 16 were positive for WNV based on RT-PCR technique. The positive pools were from four nesting colonies of birds. Out of 37 cattle egret squabs examined, 37.8% had serum-neutralizing antibodies to WNV. WNV RNA was also detected in one out of 15 pools of R. turanicus, in one out of 21 pools of O. sylviarum, and in one out of 18 pools of D. gallinae, while 63 pools of A. reflexus, 11 of R. sanguineus, and 30 of Hyalomma spec. were negative. The role of mites and ticks in maintaining the endemic state of WNV in Israel is discussed.

Are Rice Fields in Southeastern Australia an Adequate Substitute for Natural Wetlands as Foraging Areas for Egrets?

Within the Murray-Darling Basin of eastern Australia there has been a general decline in the abundance of wading birds. Loss of wetlands caused by river regulation and irrigated agriculture is considered to be the main cause. We assessed the adequacy of irrigated rice fields as substitutes for natural wetlands for foraging egrets during the breeding season in one study area around a mixed colony of egrets in southeast Australia. For aerially sown rice crops, which represented 85% of all rice in the general area, the densities of foraging Intermediate Egret (Egretta intermedia) and Great Egret (Ardea alba) tended to reach a maximum four to six weeks after sowing of the rice crop, and declined thereafter. The decline phase was correlated with decreasing prey capture rates and a shift from vertebrate prey to less profitable invertebrate prey, and coincided with the start of the egrets’ main chick rearing period when food demands would have been high. Even at maximum densities it was estimated that only 5-13% of the Intermediate Egrets and Great Egrets that were available to feed actually did so in the rice growing areas within 6.5 km of the colony. In contrast, Cattle Egret (Bubulcus ibis) densities in rice fields did not decline until after their young fledged. They fed almost exclusively on insects and their prey capture rates showed no seasonal decrease. Up to 60% of the available Cattle Egrets were found feeding in the rice fields within 6.5 km of the colony. It is concluded that rice fields provide a good foraging habitat for the Cattle Egret and may be contributing to the spread of this invasive species, but that they are probably not a preferred foraging habitat for the Intermediate Egret and the Great Egret.

Importance of Furugelm Island in the Sea of Japan for wetland birds: the first record of a breeding colony of the Chinese egret Egretta eulophotes

A new breeding site of the globally threatened Chinese egret Egretta eulophotes was recorded on Furugelm Island in the summer of 1998. The discovery of this colony moves the breeding limit of the species more than 600 km further to the north-east in the Sea of Japan. Thirty to forty pairs of Chinese egrets were discovered on the island, which is also home to thousands of colonial seabirds as well. The egret's colony is within the Far-Eastern Marine Reserve but some of its main foraging sites lie outside the protected area and are disturbed by both tourists and hunters. More worryingly, however, the main threat to the Chinese egret's survival is a new economic development project: the Tumen River Area Development Program. We make an urgent plea for the protection of the Chinese egrets' foraging areas within the Far-Eastern Marine Reserve and recommend that a transfrontier reserve be created to enhance the protection of this important waterbird site.