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Understanding the trophic interactions and coexistence processes among waterbirds in floodplain ecosystems is of fundamental ecological importance. In the upper Paraná River floodplain, we assessed the diet of five sympatric waterbird species (Ardea alba, Ardea cocoi, Egretta thula, Nannopterum brasilianum, and Nycticorax nycticorax) and tested their differences in the diet, in addition to food overlap, differences in trophic niche breadths and stratum in the water column where they forage. The waterbirds’ stomachs were collected quarterly on the upper Paraná River floodplain, analyzed under a stereomicroscope, and the food items were identified. Only Egretta thula was classified as omnivorous, consuming various food resources, including insects, decapods, and fish. The other species were piscivorous, but differed in the types of prey. Food overlap was higher in the piscivorous species, but they exhibited high trophic niche breadth. The piscivorous waterbirds employ different strategies for exploiting food resources that allow species coexistence in the floodplain, avoiding direct competition. Our results highlight the importance of waterbirds as connectors across diverse environments, especially aquatic-terrestrial ecosystems. Since these waterbirds’ diet relies on fish, effective conservation and management strategies targeting fish communities are fundamental to maintaining biodiversity and functionality within the upper Paraná River floodplain.

Clinostomidae is a diverse family of digenean parasitizing fish-eating birds as adults and fishes as metacercariae. The species composition, within the genus Clinostomum has been steadily increasing in recent years. In Argentina, four named species of Clinostomum have been documented, accompanied by four metacercariae representing distinct genetic lineages whose adults have not been identified. This study focused on examining clinostomids in three fish species – Australoheros scitulus (ASI), Cichlasoma dimerus (CDIM), and Pimelodella laticeps (PLA) – at various localities in Argentina. We conducted both morphological and molecular characterizations of the Clinostomum metacercariae collected from these fish species. Molecular phylogenetic analyses using COI mtDNA were performed to determine the placement of these metacercariae within the clinostomid phylogenetic tree. Clinostomum ASC represents a distinct lineage, morphologically distinguishable from other sequenced metacercariae due to its body shape (widest anteriorly and becoming slender towards the posterior end); this lineage was found to be closely related to C. caffarae. While Clinostomum CDIM and Clinostomum PLA exhibited morphological differences, they clustered together genetically with metacercariae reported in previous studies as Clinostomum L3 and Clinostomum CVI. This outcome, coupled with a low genetic distance (0 to 3%), suggests that they are conspecific with metacercariae found in fish across Mexico, Costa Rica, and Argentina. In light of the extensive diversity of fish species in Argentine freshwater ecosystems (over 500 species), and considering the relatively constrained extent of prior investigations, the anticipation of unearthing additional Clinostomum species or lineages is plausible.

Wading birds are key components of wetlands, transporting matter, energy, contaminants and associated organisms among limnetic, estuarine, terrestrial and coastal ecosystems. The role of cocoi herons (Ardea cocoi) in connecting these ecosystems was studied in the only known estuarine and limnetic colonies in coastal plains of southern Brazil. Food obtained by parents around colonies when foraging for chicks and themselves was used to assess diet, by the analysis of 50 pellets, gastrointestinal contents and spontaneous regurgitated samples, as well as the analysis of stable isotopes (δ¹³C and δ¹⁵N) in the whole blood of 25 chicks. Cocoi herons were predominantly piscivorous in both environments, relying mainly on whitemouth croaker (Micropogonias furnieri) in the estuarine colony (47 % of samples and 36–56 % in the isotope mixing model), followed by Callinectes blue crabs and on trahira (Hoplias aff. malabaricus), in the limnetic colony (60 % of the dietary samples). However, for the limnetic colony, terrestrial and aquatic potential food sources contributed evenly to the isotopic mixing model. Furthermore, stable isotopes suggested that marine food sources, available on the coast 15 km away, were part of the diet of chicks in the limnetic colony. Complementary approaches used in the current study demonstrate that widely distributed, large-sized Ardea herons and other waterbirds are important for the connectivity of terrestrial and a range of aquatic environments. These birds contribute to the flow of matter and energy between wetlands and adjacent habitats and are key species for linking different food webs through complex and still poorly understood lateral subsides.

Se reporta por primera vez la depredación de un adulto de rana chilena (Calyptocephalellagayi) por la garza cuca (Ardea cocoi), evento que se registró en video. La observación se realizó en el verano de 2021 en una laguna ubicada en una zona perturbada por la ganadería. Este registro se añade a la escasa información acerca la depredación sobre la rana chilena, particularmente sobre adultos de gran tamaño, sugiriendo un importante rol de A. cocoi como depredador de anfibios acuáticos en Chile.

In the present study, the authors examined the role of different habitat components and their relationship with microhabitat use by three species of egret: Cocoi heron (Ardea cocoi), Great egret (Ardea alba), and Cattle egret (Bubulcus ibis), in wetlands of southern Brazil. Ardea alba and A. cocoi were not habitat-specific (e.g. vegetation cover and flooding level). Conversely, B. ibis was associated with drier microhabitats. Relative air humidity and air temperature were the main variables which correlated with the occurrence of these species and supported the plasticity of B. ibis and its predominance in drier habitats.

Great Egret (Ardea alba) and Cocoi Heron (A. cocoi) have a wide distribution in the neotropics but few data on reproductive biology for these species are available. The reproductive parameters, growth rate and diet of chicks of egret and heron in a mixed-species colony nesting were studied during the 2007 breeding season in a pampas wetland of Argentina, with 50 and 17 nests studied, respectively. Mean egret clutch size was 3.6 ± 0.5 eggs and hatching success 76%. Mean heron clutch size was 3.5 ± 0.8 eggs and hatching success 81%. The mean number of fledged egrets/egg was 0.15 and productivity 0.54 chicks per nest; for herons reproductive success and productivity were 0.17 and 0.58, respectively. In both species, the most productive clutch size was three. The first two weeks post-hatching were critical for chick survival. In egrets, the last chick to hatch had lower growth rates than the first or second hatched chicks; however in herons the first chick to hatch had higher growth rates than the second or third hatched chicks. Fish and insects were the main prey of egret chicks, while mammals and fish were the most common prey of heron chicks. Starvation was the main factor causing the relatively low breeding performance observed in both species.

The order of Pelecaniformes is composed of families Ardeidae, Thereskiornithidae, and Pelecanidae. The family Ardeidae gathers more than 60 species of herons, egrets and bitterns being one of the largest and more representative with characteristics adapted to wetlands. In the State of Rio Grande do Sul, 13 species are recorded Botaurus pinnatus, Ixobrychus involucris, Nycticorax nycticorax, Butorides striata, Bubulcus ibis, Ardea cocoi, Egretta thula, Syrigma sibilatrix, Ixobrychus exilis, Tigrisoma lineatum, Nyctanassa violacea, Egretta caerulea, and Ardea alba. The species of birds examined were Tigrisoma lineatum, Nycticorax nycticorax, Ixobrychus involucris, Butorides striata, Bubulcus ibis, Ardea alba, Ardea cocoi, Syrigma sibilatrix, and Egretta thula, a total of 30 birds from the municipalities of Pelotas, Rio Grande and Capao do Leao, in the State of Rio Grande do Sul. The animals were donated, after death, by Nucleo de Reabilitacao da Fauna Silvestre and Centro de Triagem de Animais Silvestres of Universidade Federal de Pelotas (NURFS-CETAS/UFPel).

The feeding ecology of Ardea cocoi were analysed based on 29 herons captured on the Carabajal island (Santa Fe, 31°39'S, 60°42'W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, standardisation, circadian rhythm of feeding activity and habitat preference. The trophic spectrum was made up of 17 taxonomic entities, mainly fishes (IRI = 16,000), followed by mammals and amphibians (IRI = 8,000). The highest percentage of prey size was found in the interval 151→200 mm. The amplitude of the trophic niche ranged between 1.98 and 4.21, and the feeding efficiency between 89.9 and 99.9%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded no significant results (r s = 0.078, P>0.001). The rhythm of feeding activity responded to the bell-shaped model. Aquatic vegetation was the unit of vegetation and environment selected more frequently.

The Gulf of Panama is a highly productive marine ecosystem at the southern edge of North America. Although the Gulf’s aquatic bird populations have been remarked upon by ornithologists for over 50 years, nesting populations have been neither systematically studied nor completely characterized. In 2005 and 2006, the entire Gulf of Panama was inventoried to document the nesting status of seabirds and other colonial waterbirds. Over 50,000 birds of 20 species nesting at 57 sites were documented. Seabirds nested during the dry season, the period of oceanographic upwelling. Coastal colonial waterbirds nested at the end of the dry season and in the early wet season, when inland feeding habitats were optimal. Brown Pelicans (Pelecanus occidentalis) were the most numerous seabird with over 4,800 nests and 10,000 individuals counted. Over 3,600 Neotropic Cormorant (Phalacrocorax brasilianus) nests and over 2,200 Magnificent Frigatebird (Fregata magnificens) nests were documented. Cattle Egrets (Bubulcus ibis) were the most abundant colonial wading birds, followed by Great Egrets (Ardea alba). Great Egrets were the first wading birds to nest, Cattle Egrets the last. Seven sites contained over 1,000 nests. Colony locations and numbers differed markedly from the historic literature. Some historic information is erroneous, but other differences reflect changes in distribution. More nesting Brown Pelicans and Sooty Terns (Sterna fuscata) and fewer Neotropic Cormorants were found than expected from the literature. New sites documented included some of global or regional conservation importance. This paper presents the first breeding records for Panama of Little Blue Heron (Egretta caerulea), Glossy Ibis (Plegadis falcinellus), and Bridled Tern (Sterna anaethetus), and third record for Cocoi Heron (Ardea cocoi). There is no evidence for long-term declines of seabirds or colonial wading birds in the Gulf of Panama. Populations reaching conservation thresholds globally or biogeographically include Brown Pelican, Bare-throated Tiger-Heron (Tigrisoma mexicanum), White Ibis (Eudocimus albus), Glossy Ibis, and Bridled Tern. The Black-crowned Night-Heron (Nycticorax nycticorax) exceeded conservation thresholds for Central America. Six new sites of global importance for bird conservation were identified and the continued importance of another site confirmed. The continued health of the waterbird populations of Panama will depend on environmental education and protection of important colony sites from disturbance and development.

Dolichorchis lacombeensis sp. nov., a digenean parasite of the gut of the cocoi heron, Ardea cocoi (L.), is described as a new species from Buenos Aires Province, Argentina. This new species most closely resembles D. buteii and D. tregenna in the distribution of the vitelline follicles, which reach the intestinal bifurcation in the forebody. D. buteii can be distinguished from D. lacombeensis sp. nov. by the distribution of the vitelline follicles in the hindbody, which are concentrated in midline, by the presence of a sphincter in genital pore and by the size of holdfast organ and posterior testis, which are larger, (240–400 × 176–240 and 315–464 × 240–410 µm, respectively). D. tregenna differ from the new species by their larger measurements (pseudosuckers’ length 90–100, pharynx 52–90 × 50–70 and eggs 89–104 × 48–68 µm).