Little Blue Heron Research Articles

Influence of pollutants on migratory bird populations in the Palmar estuary

The study was conducted on the beach and estuary of Comuna Palmar during October 2017 to January 2018, considering a total area of 78,460 m², subdivided into A1, A2, A3, A4, respectively, for the data collection on the influence of pollutants on the existing birds in this area, for the study of birds the methodology of Antonio Cánepa & Juan Aguirre of 2002 was applied, counting 15,273 ind, distributed in 26 species of birds, migratory and resident, within the 4 study areas, the simple variance analysis showed area 2 with the greatest diversity of species and area 4 with the greatest variety of pollutants. The results showed that Magnificent Frigatebirds (Fregata magnificens), with 9,402 individuals, represented 62% of the total. A single individual of Great Blue Heron (Egretta caerulea), White Ibis (Eudocimus albus), Lesser Yellowlegs (Oceanodroma microsoma), and Lesser Yellowlegs (Tringa flavipes). A total of 2,230.32 pounds of contaminants were collected; the greatest amount of plastic mooring lines with 672.40 pounds, and the least amount of powdered resin debris with 3.2 pounds, with an incidence in the resting areas of the organisms.

Evaluating temporal and spatial transferability of a tidal inundation model for foraging waterbirds

AbstractFor ecosystem models to be applicable outside their context of development, temporal and spatial transferability must be demonstrated. This presents a challenge for modeling intertidal ecosystems where spatiotemporal variation arises at multiple scales. Models specializing in tidal dynamics are generally inhibited from having wider ecological applications by coarse spatiotemporal resolution or high user competency. The Tidal Inundation Model of Shallow‐water Availability (TiMSA) uniquely simulates tides to empirically derive a time‐integrated measure of availability for a shallow‐water depth range defined by the user. To evaluate temporal and spatiotemporal transferability, we employed TiMSA at the development site in the Florida Keys and at novel subsites in the Florida Bay (application site) under a different time period (application period). We used foraging little blue herons (Egretta caerulea) as the ecological unit with which to constrain the model's “water depth window,” that is, range of water depths to estimate shallow‐water availability. At the development site, temporally consistent water depth windows contrasted with interannual variation in shallow‐water availability, which revealed short‐term changes in Little Blue Heron foraging habitat. At the application site, water depth accuracy varied by subsite and was correlated with spatial error in bathymetric elevation. Although TiMSA parameters were sensitive to environmental temporal variation and uncertainty in spatial data, a spatially explicit water depth window generated reliable estimates of shallow‐water conditions over space and time at the development and application sites. By exploring the contributing factors to model error, we provide solutions to reduce uncertainty of TiMSA parameters at potential application sites and recommendations for addressing bathymetric inaccuracy in digital elevation models. Accurately quantifying spatiotemporal changes of shallow water has implications for monitoring habitat conditions for tidally influenced species and projecting future changes to coastal ecosystems in response to anthropogenic stressors and natural disturbances such as sea level rise.

COMPARAÇÃO DA EFICIÊNCIA DE FORRAGEIO DAS GARÇAS EGRETTA CAERULEA E EGRETTA THULA NO ESTUÁRIO DE PARANAGUÁ, PARANÁ, SUL DO BRASIL

The foraging efficiency of birds may vary according to local conditions as a result of the balance between energy consumption and expenditure. The foraging efficiency of Egretta thula (adults n=11) and Egretta caerulea (adults n=69 and juveniles n= 17) was compared in Paranaguá city estuary, in Paraná, Brazil. In 14 hours of observation divided into 2 minutes sessions per individual, were recorded foraging site (mud or shallow water), number of steps, total peckings and successful peckings, and were calculated the success rates, energy effort and capture efficiency. In shallow water E.thula was more efficient than E. caerulea. There was no intraspecific differences in E. thula regarding environments. Adults of E. caerulea were more efficient than juveniles, with greater efficiency in mud than in shallow waters environments. Differences in foraging efficiency between species may be related to the type of foraging according to feeding location.

Breeding Phenology and Reproductive Success of Little Blue Herons (Egretta caerulea) in an Urban Mixed-Species Colony

As human populations continue to expand into suburban and rural areas, conflicts with wildlife are likely to increase. Many populations of long-legged wading birds (Family Ardeidae) face the challenge of human disturbance both at feeding sites and breeding colonies. Little Blue Herons (Egretta caerulea) are medium-sized wading birds that often join egrets and other herons in mixed-species breeding colonies. In June and July 2018, a random sample of Little Blue Heron nests located in an urban colony were monitored from incubation to fledging. The goals of this study were to (1) characterize adult nest-activity patterns over the course of the breeding cycle, and (2) document Little Blue Heron reproductive success in an urban colony and identify sources of human disturbance. Instantaneous samples with 5-min intervals were used to record adult activity during 50 h of observation at 24 nests. An additional 77 h of continuous observation at two different nests documented fine-scale activities and changes in nesting status. Observations made at random times during morning, midday, and evening periods yielded 636 nest-hours across all breeding stages. During incubation, attending parents mostly sat (63 %) or stood (23 %) in or near their nests, spent less time in nest maintenance (5 %) and self-maintenance (scratching, preening; 5 %), and seldom (< 1 %) left the nest unprotected. By the end of the breeding cycle, nests were unattended 69 % of the time. The 26 monitored nests fledged a total 39 chicks (1.4 ± 0.3 chicks/nest attempt). The 16 successful nests (61 % of all nests) fledged 2.4 ± 0.2 chicks. Known causes of nest failure included destruction or usurpation by Cattle Egrets (Bubulbus ibis) and predation by Black-crowned Night-herons (Nycticorax nycticorax). Sources of disturbance included dogs allowed in the colony, intentional loud noises, and human presence. We compare reproductive success at this urban colony to that in less disturbed colonies reported in the literature.

Prey consumed by wading birds in mangrove swamps of the Caribbean coast of Colombia

ABSTRACTThe diet composition of wading birds was studied in mangrove swamps of the north western Caribbean coast of Colombia during the non-breeding season for Little Blue Heron (Egretta caerulea), Tricolored Heron (Egretta tricolor) and Snowy Egret (Egretta thula), and during the breeding season for Agami Heron (Agamia agami), Cocoi Heron (Ardea cocoi), Boat-billed Heron (Cochlearius cochlearius) and Bare-throated Tiger-Heron (Tigrisoma mexicanum). One-hundred and thirty-two birds were captured, and 32 regurgitations and nine stomach samples were collected. Except for Little Blue Heron, these species ate mostly small fish. Representatives of Poecilidae, Gambusia sp. and Poecilia sp., were the most important prey taken by Snowy Egret and Tricolored Heron, with significant differences in the weight, and standard length of Gambusia sp. consumed by both birds, as well as in the weight of Poecilia sp. The other five wading bird species were poorly represented on our samples, but never the less contribute to first records of their diet. The known diet of all species is briefly reviewed.

Nesting Island Creation for Wading Birds

Many long-legged wading birds such as little blue herons (Egretta caerulea), great blue herons (Ardea herodius), and great egrets (Ardea albus) nest together in large aggregations called breeding colonies. Although different species vary in their habitat preferences, wading birds have several common requirements for nesting. Colony sites must provide protection from predators, nesting materials, and nearby foraging areas (Hafner 2000). In the past, wading birds nested in natural wetland habitats that are becoming increasingly scarce as wetland habitats are continually altered or degraded to accommodate human needs. The future success of wading bird populations may be determined by how well they cope with manipulated foraging and nesting habitats. In this document, we make recommendations on the creation of nesting islands for long-legged wading birds. This document is CIR1473, one of a series of the Wildlife Ecology and Conservation Department, UF/IFAS Extension. Original publication date May 2005.&#x0D; CIR1473/UW223: Nesting Island Creation for Wading Birds (ufl.edu)

Spatial patterns of mercury contamination and associated risk to piscivorous wading birds of the south central United States.

Piscivorous birds are top predators in aquatic ecosystems and are vulnerable to mercury (Hg) exposure and associated adverse health effects. In some areas of North America, the health risk posed to piscivorous birds by Hg contamination has not been characterized because concentrations of Hg in bird tissues have not been extensively monitored. When data on Hg in tissues of piscivorous birds are not available, the concentration of Hg in the blood of piscivorous birds can be estimated from the concentration of Hg in prey fish. We used concentrations of Hg in different lengths of a proxy prey fish, bluegill (Lepomis macrochirus), to estimate the concentration of Hg in the blood of 4 species of adult piscivorous wading birds (little blue herons [Egretta caerulea], green herons [Butorides virescens], great egrets [Ardea albus], and great blue herons [Ardea herodias]) in 14 ecoregions of the south central United States. The 4 species of birds consume different sizes of fish with different concentrations of Hg and were predicted to have different concentrations of Hg in their blood, with little blue herons < green herons < great egrets < great blue herons. For each species of bird, there were significant differences in average estimated concentrations of Hg in blood between ecoregions, with estimated concentrations of Hg in blood increasing with Hg deposition. The level of predicted risk varied with ecoregion and bird species and was highest for great blue herons. We recommend that future studies of Hg contamination of piscivorous wading birds of the southern United States focus on great blue herons in water bodies within ecoregions that have high Hg deposition. Environ Toxicol Chem 2019;38:160-166. © 2018 SETAC.

Time‐integrated habitat availability is a resource attribute that informs patterns of use in intertidal areas

AbstractIn dynamic environments, resource availability may change by several orders of magnitude, over hours to months, but the duration of resource availability is not often included as a characteristic attribute of resources even though temporal resource dynamics might limit patterns of use. In our study of wading birds foraging in intertidal areas, tides cause large changes in the areal extent of shallow‐water foraging habitat (i.e., the resource), but tides also constrain the duration of availability, which is often overlooked. We hypothesized that temporal constraints on habitat availability from tides would be reflected in patterns of habitat use by foraging birds. We estimated the time‐integrated habitat availability and compared it to traditional habitat attributes (seagrass cover, substrate type, instantaneous water depth, and proximity to mangrove islands or deep water) that have strong evidential support for influencing patterns of use. To evaluate our hypotheses, we quantified habitat attributes at intertidal areas in the Florida Keys, USA, where wading birds were observed foraging (Little Blue Heron, Egretta caerulea: N = 183; Great White Heron, Ardea herodias occidentalis: N = 162). We tested for nonrandom use by sampling habitat attributes at two spatial scales around the observed feeding locations and we analyzed the data using a conditional logistic regression model. There was no evidence that seagrass cover or substrate explained patterns of use. The proximity of foraging locations relative to mangroves and to deep water were important at both spatial scales but had lower effect sizes (odds ratios) than time‐integrated habitat availability and water depth, and the latter may only serve as a physical constraint on access. We found support that time‐integrated habitat availability was a distinct resource attribute, had the greatest effect size (four‐ to eightfold change in relative probability of use), and best explained patterns of habitat use at the largest spatial scale. In studies of resource use where changes in resource availability are nonlinear or when strong constraints on access are imposed by behavior, incorporating time‐integrated estimates of resource availability into analyses can improve insights into spatiotemporal patterns of resource use.

New and noteworthy records of waterbirds from Paraguay

Previously unpublished new and noteworthy Paraguayan reports of Anatidae, Ardeidae, Podicipedidae and Rallidae are provided. The first documented records of Speckled Teal Anas flavirostris, Yellow-billed Pintail Anas georgica, Blue-winged Teal Anas discors and Red-gartered Coot Fulica armillata are detailed with a review of previous undocumented reports of the species. Additional records of a further five rarely-recorded waterbird species are also reported: Silvery Grebe Podiceps occipitalis, Great Grebe Podiceps major, Little Blue Heron Egretta caerulea, Cinnamon Teal Anas cyanoptera and Red Shoveler Anas platalea. The new additions add up to a total of 123 waterbird species documented to occur in Paraguay.

Attraction of Nesting Wading Birds to Alligators (Alligator mississippiensis). Testing the ‘Nest Protector’ Hypothesis

Ecological facilitation (mutualism and commensalism) appears to be a strong force shaping biotic communities, and may be more likely in stressful and dynamic environments like wetlands. We examined a specific type of mutualism, ‘protective nesting associations,’ between herons and egrets (Ardeidae) and American alligators (Alligator mississippiensis). We predicted that wading birds would be attracted to sites with alligators. A survey of potential nesting sites in the Everglades showed strong nonrandom association, with wading birds never nesting without alligators. At previously unoccupied nesting colony sites, we experimentally manipulated apparent densities of alligators and birds using alligator and bird decoys. Small day-herons (little blue herons (Egretta caerulea), tricolored herons (Egretta tricolor), and snowy egrets (Egretta thula)) were significantly more numerous at sites with both alligator and bird decoys than other treatments. These findings together support the hypothesis that wading birds actively choose predator-protected nesting locations based in part on information from both conspecifics and alligators, and suggest that the mechanism supporting this habitat choice is primarily due to nest protection benefits the alligators inadvertently provide. We propose that this interaction is strong and could be geographically widespread, and suggest that it may be critical to shaping management and conservation of wetland function.

Linking wading bird prey selection to number of nests

Establishing a link between food availability and productivity is often central to the recovery of declining populations; however, differences in prey selection may influence how populations are affected by changes in prey availability. We determined prey selection and prey availability for 3 wading bird species, and investigated the effects of prey availability on the number of nests initiated by 6 wading bird species in the Florida Everglades, USA. To determine prey selection, we compared food items recovered from tricolored heron (Egretta tricolor), snowy egret (Egretta thula), and little blue heron (Egretta caerulea) nestlings to aquatic prey availability from throw-traps across the Everglades landscape from 2012 to 2014. Tricolored heron and snowy egret prey composition was statistically similar across years, with the majority of prey biomass coming from relatively large (>1.9 cm) marsh fish. Little blue heron prey composition differed from the other wading bird species, and contained a higher percentage of grass shrimp (Palaemonetes paludosus) and exotic fish species. Numbers of small heron nests were positively influenced by the availability of large marsh fish across the landscape, whereas numbers of nests for other wading bird species (wood stork [Mycteria americana], great egret [Ardea alba], white ibis [Eudocimus albus]) were not. Our results suggest differences among wading bird species in their prey selection and availability. Although small heron foraging may seem restricted by their specialization on marsh fishes, their short nesting cycles allow for the phenological flexibility to delay nesting until foraging conditions are optimal. Conversely, wood storks with longer nesting cycles are more temporally constrained but have greater flexibility in prey items and foraging range. The annual number of small heron nests may be more robust to hydrological variability as a result of management action or global change than the number of wood stork nests. The temporal constraints of nesting by wood storks indicate that management of supporting wetland systems should provide continuous habitat availability during the nesting season. © 2016 The Wildlife Society.

Effects of tidal periodicities and diurnal foraging constraints on the density of foraging wading birds

ABSTRACT In intertidal zones, tidal cycles reduce water depths and provide areas of shallow water where wading birds can forage for aquatic prey (water depths 0–50 cm). However, a bird that forages diurnally can make use of only a portion of the tidal cycle, which can limit fulfillment of energetic demands. Furthermore, daily and biweekly (spring–neap) tides may compound effects on shallow-water availability for foraging birds. However, the relative effects of daily and biweekly tidal periodicities on the foraging ecology of wading birds are seldom investigated due to a lack of appropriate tools. Therefore, we developed a tidal simulation model to provide dynamic spatiotemporal estimates of the availability of water depths that are within the upper and lower bounds of the birds' foraging water depth limits (“shallow-water availability”). We studied two wading bird species, the Little Blue Heron (Egretta caerulea), a daytime-only forager, and the Great White Heron (Ardea herodias occidentalis), which feeds...

A new species of &lt;i&gt;Microphallus&lt;/i&gt; (Trematoda: Microphallidae) from Venezuela

During 1997-1999, a total of 94 crabs, Uca rapax were collected from La Sabana, La Ceiba and El Paujil, Sucre State, Venezuela. Of these 36 were infected with metacercariae. Two parasites were located in the abdominal muscles and one under the tissue of carapace and gonad. These metacercariae grew to adults in the following genera: Levinseniella, Microphallus and Maritrema, in the period of 2-5 days after feeding experimentally to the rat Rattus norvegicus, mice Mus musculus and duck Cairinia moschata. Specimens of the genus Microphallus were described herein as a new species M. sabanensis. The life cycle of M. sabanensis sp.nov. were studied experimentally using rat, mice and duck. All developmental stages and the adult are described. In addition, M. sabanensis was collected from wild birds Anas discors, Pluvialis squatarola, Butorides striatus, Egretta caerulea and Nycticorax violaceus from the same localities.

Gryporhynchidae (Cestoda: Cyclophyllidea) in Mexico: species list, hosts, distribution and new records.

As a result of this study, 8 new host (Botaurus lentiginosus for Glossocercus caribaensis and Valipora mutabilis; Egretta caerulea for Valipora minuta; Egretta thula for Glossocercus cyprinodontis; Egretta tricolor and Nycticorax nycticorax for Glossocercus caribaensis; Pelecanus occidentalis and Platalea ajaja for Paradilepis caballeroi) and 31 new locality records for gryporhynchid cestode species in Mexico are presented. With these data, the total number of species of this group of helminths in Mexico becomes 25 (19 named species and 6 unidentified taxa), which have been registered as parasites of fishes (47 host species) and (or) birds (20 host species). This information comes from 102 localities, pertaining to 20 of 32 Mexican states. Five of the 25 taxa have been exclusivelly collected in fishes, 7 in fish-eating birds, and 13 in both groups of hosts. The most frequent metacestodes found in Mexican fishes are the merocercoids of Cyclustera ralli, Valipora mutabilis, Parvitaenia cochlearii and Valipora campylancristrota; in adult stage, Glossocercus caribaensis was the species with the largest host spectrum, while Paradilepis caballeroi has the widest distribution range. The work includes parasite/host lists, as well as habitat, distribution, references and information on specimens' deposition.

Diversidade e abundância sazonal da avifauna em duas planícies de maré no estuário da baía da Babitonga, norte de Santa Catarina

Informações sobre a ocorrência de aves nos ambientes estuarinos de Santa Catarina ainda são escassas. O objetivo deste trabalho foi registrar a diversidade, abundância e variação sazonal das aves em duas planícies de maré na baía da Babitonga. As amostragens foram realizadas durante um ano (maio de 2006 a abril 2007). No total foram identificadas 25 espécies, sendo 15 no Linguado (LG) e 24 na desembocadura do Monte de Trigo (MT). Apenas uma espécie foi exclusiva no LG Himantopus melanurus (Vieillot, 1817), enquanto dez espécies ocorreram apenas no MT. O número de espécies em MT foi superior ao encontrado em LG. A espécie mais abundante em MT foi Rynchops niger (Linnaeus, 1758) e em LG foi Egretta caerulea (Linnaeus, 1758). Durante alguns meses foram registradas espécies migratórias neárticas em ambas as áreas, o que representou um acréscimo na diversidade. A extensa planície de maré formada pelo fechamento do canal do Linguado tem sido muito ocupada por aves, possivelmente pela maior disponibilidade de alimento.

Polychlorinated Biphenyl (PCB) congener concentrations in aquatic birds. Case study: Ilha Grande Bay, Rio de Janeiro, Brazil

Livers from 108 birds found prostrate or dead in Ilha Grande Bay between 2005 and 2010 were analyzed for 16 PCB congeners (IUPAC numbers 8, 18, 28, 31, 52, 77, 101, 118, 126, 128, 138, 149, 153, 169, 170, and 180). The species analyzed were Egretta caerulea (Linnaeus 1758), Nycticorax nycticorax (Linnaeus 1758), Egretta thula (Molina 1782), and Ardea cocoi (Linnaeus 1766). The analysis were performed using Origin software (7.5, 2004) with a significant level of p<0.05. Data were checked for adherence to the standard assumptions of parametric tests using the Kolmogorov-Smirnov test for normality and the Levene's test for homogeneity of variances. This has revealed differences in concentration for some congeners. Results indicate relatively low PCBs contamination in aquatic birds, but it is implied the close relationship of environmental contamination, showing potential power of widespread biological and mutagenic adverse effects in trophic levels, and therefore, signalling risk to human health.

Quality of Flooded Rice and Fallow Fields as Foraging Habitat for Little Blue Herons and Great Egrets in the Everglades Agricultural Area, USA

Wading birds have been observed foraging in agricultural wetlands worldwide where natural wetlands have become lost, degraded, or seasonally dry, yet the ability of wading birds to satisfy daily energy requirements in agricultural wetlands has been little studied. The ability to meet daily energy requirements for Little Blue Herons (Egretta caerulea) and Great Egrets (Ardea alba) foraging in flooded rice and fallow fields of the Everglades Agricultural Area (EAA) was evaluated during April-June 2008 and 2009. Focal samples were used to measure capture rates (captures/min), identify prey and estimate captured prey size, and calculate energy budgets for both species. Within flooded fields prey density was measured and foraging sites and random locations were compared. Habitat variables did not differ between foraging sites and random locations. Vegetation cover and prey abundance increased in rice fields over time and were greater in rice than fallow fields. Small prey, dominated by fish, were captured by both species and corresponded to prey sampled. Most wading birds in June were observed in newly flooded fallow fields despite lower prey densities. Little Blue Herons met daily energy requirements for both years; but Great Egrets did not, likely due to predominantly small prey, increasing vegetative cover in rice fields, and lower prey densities in newly flooded fallow fields. Although Great Egrets did not meet daily caloric requirements, the EAA may still function as an important transitional habitat at a time when foraging resources in the region are limited.

Abundance, breeding and food of the Little Blue Heron Egretta caerulea (Aves, Ardeidae) in the Patos Lagoon estuary, a recently colonized area in southern Brazil

We document the expansion of the breeding distribution of the Little Blue Heron Egretta caerulea (Linnaeus, 1758) to 850 km beyond its previous southern limit in South America. In addition we present data on abundance, breeding biology and food of the species in the Patos Lagoon estuary, the area which the species recently colonized. The maximum abundance recorded in the breeding colony and in a nocturnal roosting site was 53 and 49 individuals respectively. Nesting occurred from September to March. Birds nested in a mixed breeding colony together with about 3,000 breeding pairs of seven other species of Pelecaniformes, in a swampy forest near the margin of the estuary. Five nests were between 1.5 and 4.3 m from the ground, on the shrub Daphnopsis racemosa (Thymelaeaceae), on the trees Sebastiana brasiliensis (Euphorbiaceae) and Mimosa bimucronata (Leguminosae), or on the bamboo Bambusa sp. (Poaceae). Four nests produced two fledglings each, while one nest was abandoned. Of 13 grouped samples of food regurgitated by five nestlings, Pink Shrimp Farfantepenaeus paulensis (Perez-Farfante, 1967) constituted 70% in mass, while total length of ingested fishes and shrimps varied mostly between 20 and 50 mm. Estuarine prey items represented 99% of the total food mass. The recent southward expansion of the breeding range of the Little Blue Heron in South America may be a response to climate warming of the Patos Lagoon estuary. Degradation of estuaries in the southwestern Atlantic may also be forcing the birds to breed in areas outside previous geographical range.

Estimation of heavy metals in little blue heron (Egretta caerulea) collected from sepetiba bay, rio de janeiro, brazil

Samples of liver and kidney of Little Blue Heron (Egretta caerulea) collected on Sepetiba Bay, Rio de Janeiro, Brazil, were analysed for their copper, zinc, cadmium, lead, chromium and nickel content. Mean concentration levels in liver and kidney (μg.g-1 dry weight) were 6.32955 and 6.57136 (Cd); 78.17409 and 96.89409 (Zn); 44.01727 and 65.20864 (Cu); 41.15091 and 39.62318 (Pb); 2.80091 and 4.16455 (Cr); and 9.27182 and 9.91091 (Ni), respectively. Results indicate relatively high trace metal contamination in E. caerulea, showing potential widespread biological and mutagenic adverse effects at trophic levels, and therefore, signalling risk to human health.

Unravelling feeding territoriality in the Little Blue Heron, Egretta caerulea, in Cananéia, Brazil

Habitat use by the Little Blue Heron (Egretta caerulea) and discovery of feeding territoriality are discussed here. The results showed the existence of a territorial individual defending an area (2,564.46 +/- 943.56 m(2)) close to the mangrove, and non-territorial individuals (9.17 +/- 2.54) in the rest of a demarcated area (mean area for the non-territorial: 893.25 +/- 676.72). A weak positive correlation (r = 0.47, df = 46, p < 0.05) was found between the overlapping of territorial and non-territorial individuals (2.85 +/- 3.07 m(2)) and the mean overlapped area for territorial individuals (171.41 +/- 131.40 m(2)). Higher capture (1.52 +/- 1.14 x 1.00 +/- 1.37 catches/minutes) and success rates (0.45 +/- 0.31 x 0.21 +/- 0.27) and lower energy expenditure rates (45.21 +/- 14.96 x 51.22 +/- 14.37 steps/minutes; and 3.65 +/- 2.55 x 4.94 +/- 3.28 stabs/minutes) were observed for individuals foraging in areas close to the mangrove. The results suggest that the observed territorial behaviour is more related to a number of food parameters than to intruder pressure, and also that the observed territoriality might be related to defense of areas with higher prey availability.