Blue Heron Research Articles

Evaluating washing techniques to eliminate external contamination of trace elements in bat fur and bird feathers

Non-invasive proxies, such as fur and feathers, are likely to be increasingly used to assess the potential exposure of chemicals, including trace metals and metalloids. However, the amount of external contamination is usually unknown, and there is no standard method for removing external contamination of trace metals in fur or feathers. To date, 40 % of studies published related to the measurement of trace metal levels in fur or the hair of non-human mammals and 24 % of studies in feathers do not state any washing methods or did not wash the samples before analysis. We assessed three washing techniques to remove external contamination of arsenic (As), lead (Pb), and zinc (Zn) from bat fur. We selected the three most frequently used fur washing methods from literature. To test these methods, fur samples from great flying foxes (Pteropus neohibernicus neohibernicus, n=15 individuals) from Papua New Guinea preserved over eight decades (AMNH, USA) were used. Percentages of trace metal removed are 87.19 % (SD= 12.28), 92.99 % (SD= 5.5) and 88.57 % (SD= 9.33) for As, 54.72 % (SD= 31.64), 55.89 % (SD= 37.87), and 53.93 % (SD= 41.28) for Pb, and 74.03 % (SD= 22.96), 22.93 % (SD= 73), and 24.95 % (SD= 49.5) for Zn using M2, M3, and M4, respectively. We also assessed four washing techniques to remove external contamination of arsenic (As), mercury (Hg), and zinc (Zn) from bird feathers. We identified the four most prevalent washing techniques in the literature used for feathers. We used feathers from the great horned owl (Bubo virginianus) and the great blue heron (Ardea herodias) to test these methods. Percentages of trace metal removed are 34.35 % (SD= 44.22), 69.22 % (SD= 36.5), 62.59 % (SD= 48.37), and 80.89 % (SD= 14.54) for As, 66.97 % (SD= 13.26), 29.4 % (SD= 67.06), 49.68 % (SD= 42.33), and 28.88 % (SD= 69) for Hg, and <0 % (SD= 80.1), 0 % (SD= 29.55), 11.23 % (SD= 47.73), and 57.09 % (SD= 21.2) for Zn using M2, M3, M4, and M5, respectively. This study shows the importance of washing fur and feather samples prior to trace metals analyses in ecotoxicology and biomonitoring studies.

Slow and steady: auditory features for discriminating animal vocalizations.

We propose that listeners can use temporal regularities - spectro-temporal correlations that change smoothly over time - to discriminate animal vocalizations within and between species. To test this idea, we used Slow Feature Analysis (SFA) to find the most temporally regular components of vocalizations from birds (blue jay, house finch, American yellow warbler, and great blue heron), humans (English speakers), and rhesus macaques. We projected vocalizations into the learned feature space and tested intra-class (same speaker/species) and inter-class (different speakers/species) auditory discrimination by a trained classifier. We found that: 1) Vocalization discrimination was excellent (> 95%) in all cases; 2) Performance depended primarily on the ~10 most temporally regular features; 3) Most vocalizations are dominated by ~10 features with high temporal regularity; and 4) These regular features are highly correlated with the most predictable components of animal sounds.

Morphological and molecular data establishes Clinostomum dolichorchum n. sp. (Digenea: Clinostomidae) in the great blue heron Ardea herodias L. and American bullfrog Rana catesbeiana Shaw.

Clinostomum is a cosmopolitan genus of trematodes that infect piscivorous birds, freshwater molluscs, freshwater fish and amphibians. Herein, a novel species of Clinostomum is described based on morphological and molecular data from an adult in the oral cavity of the great blue heron Ardea herodias and metacercariae collected from the gills and skin of American bullfrog tadpoles Rana catesbeiana. The novel species shares similar qualitative and quantitative morphological features with a congener, Clinostomum marginatum, which has overlap in host and geographic distribution. The most notable morphological difference when compared to C. marginatum is the greater posterior testis length of the novel species. Molecular data resolved similarities with morphological comparisons to nominal species and supports the establishment of a novel species. Molecular data include partial small ribosomal subunit (18S rRNA gene), ribosomal internal transcribed spacer regions (ITS1, 5.8S rRNA gene, and ITS2), partial large ribosomal subunit (28S rRNA gene), cytochrome c oxidase subunit 1 gene (cox1), and nicotinamide adenine dinucleotide dehydrogenase subunit 1 gene (nad1) sequences. Phylogenetic analyses place the novel species in a sister clade to C. marginatum. Morphological and molecular data, combined with phylogenetic analyses support the establishment of Clinostomum dolichorchum n. sp.

A comparison of initial harvest results from four partial harvest systems at the Blue Heron Demonstration Forest

Demonstration forests have been established across the northern hardwoods of the United States to assess the economic and environmental implications of partial harvest systems, such as single tree selection and diameter limit cutting. Single tree selection has been studied at several sites in the northern hardwoods of Canada, but there has not been a structured comparison of partial harvest systems within one site. We assessed the initial harvest results at the Blue Heron Demonstration Forest, in which four partial harvest systems – single tree selection (STS), financial maturity selection (FMS), diameter limit cutting (DLC), and crop tree release (CROP) – and a control treatment were implemented with multiple replicates within a typical northern hardwood forest in central Ontario. DLC harvested the most volume as well as basal area, followed closely by FMS. STS harvested the least basal area and volume and generated the lowest product values as well as the lowest stumpage revenue. However, STS did not harvest significantly more low vigour trees, nor did it significantly increase the proportion of basal area that is high vigour, suggesting that alternative partial harvest systems like FMS may achieve silvicultural objectives while yielding superior financial results over multiple cutting cycles.

Comparable use of tidal living shorelines and natural‐fringe marshes by herons and shorebirds

AbstractLiving shorelines (LSs) increasingly are implemented as a defense against coastal erosion and rising seas; however, their ecological function for wading birds has not been evaluated. Here, we compared heron and shorebird use of LSs (created fringe salt marshes with a wave break fronting the planted marshes) to natural‐fringe marshes (NFMs) in the Chesapeake Bay. We assessed the use between May and August in 2018 and 2019 at 13 tidal marsh pairs, each consisting of one LS and NFM site, with sites within pairs having similar surrounding land use and wave exposure. In each year, we assessed diurnal use with video cameras recording at least four 30‐min segments/day for a total of 677 h of video, and nocturnal/diurnal use with acoustic recording equipment recording 10‐min sound files every 2 h/day for a total of 160 h of recording. We quantified diurnal use by measuring the total time a species spent at a site, and nocturnal/diurnal use by estimating the probability of detection (i.e., presence/absence). We detected four heron and five shorebird species when data were aggregated across pairs and sampling methods. Using Bayesian mixed models, time of use did not differ between LS and NFM sites for great blue herons (Ardea herodias) and yellow‐crowned night‐herons (Nyctanassa violacea). In contrast, time of use was higher for green herons (Butorides virescens) and spotted sandpipers (Actitis macularis) at LS sites but tended to be higher for great egrets (Ardea alba) at NFM sites. The probability of detection did not differ between LS and NFM sites for great blue herons and great egrets (combined as “Ardea spp.” due to difficulty in differentiating calls under noisy conditions), yellow‐crowned night‐herons, and spotted sandpipers. Green herons and killdeer (Charadrius vociferous), however, tended to be detected more frequently at LS sites. Collectively, our research indicates that LSs are functionally equivalent to NFMs for herons and shorebirds. We hypothesize that the low‐profile rock sills of LS provide platforms for resting and preening and offer prey even when vegetated marshes are unavailable to short‐legged species during flooding tides. In addition to their established reduction of coastal erosion, LSs provide habitat for herons and shorebird species.

Great Blue Heron (Ardea herodias) Predation on an Abnormal California Butterfly Ray (Gymnura marmorata) and its Ecological Implications

Great Blue Heron (Ardea herodias) Predation on an Abnormal California Butterfly Ray (Gymnura marmorata) and its Ecological Implications

Automated acoustic detection of river herring (Alewife and Blueback Herring) spawning activity

AbstractObjectiveWe used passive acoustic monitoring (PAM) and automatic detection of spawning splashes to examine the timing and environmental drivers of spawning in river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis).MethodsAcoustic recordings of spawning splashes were collected from March to May 2021 in the Choptank River, Maryland, using an AudioMoth recorder. Recordings were analyzed using a random forest model on the Rainforest Connection ARBIMON platform to determine hourly presence–absence of splashes.ResultAt a seasonal scale, our results suggested two peaks in spawning activity: early March and mid‐April, corresponding with the known phenologies of Alewife and Blueback Herring. Hourly patterns in spawning activity suggested distinct diel cycles, with spawning most concentrated at dawn. In contrast, sonar fish counts collected for 1 week during the season indicated that migration occurred throughout daylight hours. We also found a potential relationship between spawning activity and the presence of great blue herons Ardea herodias.ConclusionOverall, our results demonstrate that PAM can be an efficient and affordable method for studying the spawning ecology of anadromous fish.

Four Elegies

Four Elegies

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 &amp; 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.

Oceans Away

Oceans Away David Gessner David Gessner, essay, ocean, Miami ________ The dolphins cut back and forth in front of our bow, rolling and jumping and twisting. They spotted our boat and began to chase it as we chased false albacore, and before we knew it a half dozen of them had caught up with us and were darting through the slipstream of our bow. The three of us on the boat are laughing and smiling and pointing. The dolphins seem like sleek packages of exhilaration. Joy embodied. It is November 2, 2021, and this is the first stop in a trip south to Florida that I am taking with my frequent traveling companion and old friend Mark Honerkamp. Hones, as I have forever called him, lives to fish and today he is in heaven. We launched from the dock in front of my friend Douglas's house. Douglas Cutting, a former student of mine and former fishing guide, is part owner of an old but beautifully restored wooden house that stares out at the Intracoastal Waterway in McClellanville, South Carolina, a small fishing village about three hours south of Wilmington, North Carolina, where I live. Before the day is over Hones and Douglas will have caught spotted sea-trout, red snapper, black sea bass, gag grouper, pinfish, and an oyster toadfish. The fish they don't catch, the false albacore, or albies, will provide them the most excitement, rippling the surface with their sleek backs as they devour pods of baitfish, but refusing to take the lures we offer. Even I, a nonfisherman, get into the pursuit of the albies, standing up as the lookout in the crow's nest as I scan the waters with my binoculars. On top of all the fish we are treated to the sight of bald eagles, a loggerhead turtle, and a vast variety of birds from scoters to little blue herons. But for me it is the sight of the dolphins bowriding that will remain the day's highlight. When we first moved to Wilmington, I told people that I felt like I had moved onto the set of Flipper. One of the best things about moving south was suddenly having dolphins as neighbors. It turned out that my new home was not just the center for a large community of dolphins, but a hotbed of dolphin research. One of the most exciting discoveries was recently made by three scientists, [End Page 9] one of whom, Laela Sayigh, lived only a twenty-minute paddle from me when I first moved South. Laela coauthored a paper that concluded that bottlenose dolphins convey identity information with individually distinctive signature whistles. This may not seem particularly eye-opening until you stop and think that this is just a fancy scientific way of saying that they call each other by name. There are those who deny the world beyond the human. But face to face with dolphins it is harder. ________ I have spent the last year traveling to places where the climate crisis has hit hard, and have been writing as I go, but have somehow failed to mention the large, wet elephant in the room. That is, I have mostly ignored the three-quarters of the globe that is covered by water. Thematically there is no excuse for this, but stylistically there is. I have tried to make climate small and personal, and what is larger and less personal than an ocean? But if the ocean's story is large and impersonal, it is also vital. And if we are overheating the world, this is where most of the heat is going. The heat and acidification of our ocean waters do not get the big headlines. Yet. Dolphins, I suppose, are one way of making the watery and vague more specific. But if the oceans go, so do they. After Douglas has docked and cleaned the boat, we stand around the kitchen island and drink cold beer while feasting on the fish we have caught and on the stone crabs he has prepared. We are joined by Greg, another of the house's co-owners, and his friend Drew, who has served as Greg's...

Waterbirds in constructed suburban wetlands, Eastern Denton County, Texas, USA

ABSTRACT Waterbirds were observed at 13 suburban wetlands in the Blackland Prairie of eastern Denton County, Texas, on 45 dates over a year. Five wetlands were built to improve ecosystem services in areas impacted by Lewisville Lake flood control operations; these habitat restoration wetlands were planted with diverse native flora to enhance the recovery of vegetation communities from natural seedbanks. Eight other wetlands, built to manage stormwater in residential developments, are surrounded by mixed monocultures of groomed turf grasses, with sparse shoreline plants and submerged vegetation in the littoral zone. Thirty-one species of 5,724 birds were observed, including one to nine species in each of six guilds: dabblers, divers, open water waders, dense vegetation waders, moist soil foragers and aerial piscivores. Dabblers were most abundant in count and number of species present, followed by divers and open water waders. Highly represented species were mallards, gadwalls and American coots among dabblers; lesser scaup and ringed-neck duck among divers; and great blue heron and great white egret among open water waders. Abundance averaged 539 individuals at habitat restoration wetlands and 379 individuals at stormwater management wetlands.

Great Blue Heron Forages for Fish by Bill-Vibrating

The more than 60 species in the family Ardeidae (herons, egrets, and bitterns) are known to be very creative at catching prey. Kushlan (1978) describes a total of 38 feeding behaviors for this family. Each species uses several feeding methods, but only 6 species, or about 10% of the family, are known to attract fish by vibrating their bills in water, a technique first described by Buckley and Buckley (1968). This makes bill-vibrating one of the least common feeding tactics in Ardeidae. On 10 May 2019, I observed and photographed an adult Great Blue Heron (Ardea herodias) foraging by bill-vibrating at a large pond in Dead Horse Ranch State Park, near Cottonwood, Arizona. Bill-vibrating has not previously been reported in this species.

Ornithological Passions of American Poet Celia Thaxter

American poet Celia Leighton Thaxter (1835 – 1894) was shaped by both environmental beauty and destruction she witnessed in her New England community. As a woman who spent much of her life on a small wind-swept island, she was educated by seasons and migrations that later informed her work. A brief education among Boston’s literary elite launched her creative career, where she focused on her local ecology. At that time, over-hunting and newly fashionable plumed hats and accessories had created a serious possibility of avian decimation. By creating awareness of humans’ culpability for birds’ endangerment, Thaxter’s work evoked public sympathy and contributed to social and political change.&#x0D; This essay applies ecofeminist and cultural analyses to Thaxter’s work written as part of the 19th century bird defense movement, by examining the emotional rhetoric employed and activism implied in her poems and prose about birds, specifically: “The Kittiwakes,” “The Wounded Curlew,” and “The Great Blue Heron: A Warning.” Little attention has been paid to Thaxter’s didactic poems which use birds as subjects to instruct children and adults about the fragility of birdlife and to warn of humans’ destructive behaviors. These works illustrate Thaxter’s ecological sensibility and her use of emotion and reason to communicate an ecological message. Her poetry and prose about birdlife fortified the budding Audubon Society and contributed to the birth of the environmental movement. We can learn from such poetic activism, from attention to nature turned commodity, and the dangers of depleting finite resources. In our global environmental crisis, we recognize the interwoven relationships between birds and humans. Perhaps poems can help stymie our current ecological trajectory.

Pacific Great Blue Herons (Ardea herodias fannini) consume thousands of juvenile salmon (Oncorhynchus spp.)

An array of predators that consume juvenile salmon (genus Oncorhynchus Suckley, 1861) may account for the poor returns of adult salmon to the Salish Sea. However, the Pacific Great Blue Heron (Ardea herodias fannini Chapman, 1901) is rarely listed among the known salmon predators, despite being regularly seen near salmon streams. Investigating heron predation by scanning nesting sites within 35 km of three British Columbia (Canada) rivers for fecal remains containing passive integrated transponder (PIT) tags implanted in &gt;100 000 juvenile salmon from 2008 to 2018 yielded 1205 tags, representing a minimum annual predation rate of 0.3%–1.3% of all juvenile salmon. Most of this predation (99%) was caused by ∼420 adult Pacific Great Blue Herons from three heronries. Correcting for tags defecated outside of the heronry raised the predation rates to 0.7%–3.2%, and was as high as 6% during a year of low river flow. Predation occurs during chick-rearing in late spring and accounts for 4.1%–8.4% of the Pacific Great Blue Heron chick diet. Smaller salmon smolts were significantly more susceptible to Pacific Great Blue Heron predation than larger conspecifics. The proximity of heronries relative to salmon-bearing rivers is likely a good predictor of Pacific Great Blue Heron predation on local salmon runs, and can be monitored to assess coast-wide effects of Pacific Great Blue Herons on salmon recovery.

Blue Heron

Blue Heron DJ Hills (bio) Is it the squeaky orange plastic of the inner tubesor the splash of Straw-ber-ita cansslipping from drunk grips that startles you into flight? A wild gesture of limbs points you outnearly invisible against the cloudless horizon,proof that the sky and earth were lovers once: blue as summer, featherssoft and stark as peat moss.Take me with you! someone calls as if you would;as if we have anythingto offer in return. [End Page 79] DJ Hills DJ Hills is a writer and theatre artist from the Appalachian Mountains, currently living in Baltimore. Hills's writing appears or is forthcoming in Arkansas Review, Cold Mountain Review, Lunch, and elsewhere, and their plays have been produced in and around Baltimore City. When not writing, Hills reads fiction as the Co-Senior Fiction Editor at jmww. Find them online at www.dj-hills.com Copyright © 2021 Berea College

A Physiologically Based Oiling Model (PBOM) to Predict Thermoregulatory Response in Birds

When birds are exposed to oil, their ability to thermoregulate is impaired as a result of damage to the insulative properties of their feathers. If an oiled bird is unable to maintain thermal homeostasis, hypothermia and death can follow rapidly. Physiological responses to oiling depend on several variables including environmental conditions (e.g., ambient air and water temperatures), life history of bird species (e.g., body size and habitat selection), and foraging strategies (e.g., divers, surface feeders, shorebirds). The most widely used approach to assess the effect of spilled oil on birds is the US Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Type A Natural Resource Damage Assessment (NRDA) Model for Coastal and Marine Environments. This approach addresses body size and time spent in a hypothetical slick but lacks the flexibility to assess other variables related to physiological response. We developed a dynamic physiologically based oiling model (PBOM) for birds to address this need. The PBOM has been validated against empirical data from a dose-response study in which common eiders were exposed to Statfjord A crude oil. The PBOM can be used to predict time to hypothermia for birds of differing body size and habitat preferences, in environments ranging from Arctic to subtropical. The model presently includes 5 representative bird species: common eider, spotted sandpiper, great blue heron, dovekie, and American white pelican, but could be adapted to represent almost any bird. Environ Toxicol Chem 2021;40:251-260. © 2020 SETAC.

Stable Isotopes and Parasites Indicate Feeding Ecology in Florida, USA, Wading Birds

We assessed δ13C and δ15N profiles and endoparasite community composition in Great Egrets (Ardea alba), Great Blue Herons (A. herodias), and White Ibis (Eudocimus albus) from four wildlife rescue centers (two mainland, two on islands in the Florida Keys) in south Florida, USA to elucidate feeding ecology. We detected among-species differences for δ15N but not δ13C and noted decreased δ13C enrichment in Great Egrets and Great Blue Herons (but not White Ibis) from these centers. Parasite component community and infracommunity species richness were higher in Great Egrets and Great Blue Herons relative to White Ibis, and higher in birds of the same species from mainland centers. Multivariate analysis of parasite infracommunity structure detected co-occurring clusters of parasite taxa characteristic of Great Egrets and Great Blue Herons on the one part, and of White Ibis on the other; mainland Great Egrets and Great Blue Herons had similar parasite communities and clustered separately from conspecifics from the islands. We detected a significant (negative) correlation of infracommunity species richness with δ13C but not δ15N. Lastly, parasite infracommunity Bray-Curtis similarity correlated significantly with stable isotope Euclidean distances. We conclude that the two approaches converge towards similar outcomes, providing complementary and consilient information on host feeding ecology.

Interspecific Predatory Waterbird Interactions at a RAMSAR Site

This note describes interactions between four bird species during a predation attempt by Yellow-footed Gull (Larus livens) on an Eared Grebe (Podiceps nigricollis).The interactions among species were documented on video in a mangrove (Rhizophora mangle and Avicennia germinans) area of the Ensenada La Paz (a RAMSAR site) during winter in the southwest Gulf of California, Mexico on 2 February 2019. This is the first report that has documented an effective killing attempt in the Baja California Peninsula and the second in northwestern Mexico of Yellow-footed Gull predation on Eared Grebe. Additionally, kleptoparasitism attempts against the Yellow-footed Gull by a Great Blue Heron (Ardea herodias) and Turkey Vulture (Cathartes aura) are described and suggest that those species may include prey stolen from gulls (family Laridae) more regularly than presently known based on this opportune observation.

Foraging behaviour of four avian species feeding on the same temporarily available prey

Low tide events provide terrestrial predators with ephemeral, but predictable and abundant sources of prey. Understanding the relationships between tidal cycles, prey availability, and predator abundances is vital to characterizing the ecological relationship between terrestrial predators and their marine prey. Here, we describe the foraging tactics of four common bird species in western North America — Bald Eagles (Haliaeetus leucocephalus (Linnaeus, 1766)), Great Blue Herons (Ardea herodias Linnaeus, 1758), Glaucous-winged Gulls (Larus glaucescens J.F. Naumann, 1840), and Northwestern Crows (Corvus caurinus S.F. Baird, 1858) — feeding on the same transiently accessible fish species, the plainfin midshipman (Porichthys notatus Girard, 1854). We conducted avian predator surveys at breeding beaches of plainfin midshipman across multiple years and sites. Our census data showed that Bald Eagle and Great Blue Heron abundances were higher when the tides were receding than incoming at Ladysmith Harbour, British Columbia, Canada, but the opposite trend was found for total predator abundance at a second site in Dabob Bay, Washington, USA. Glaucous-winged Gull abundance decreased over the course of the plainfin midshipman breeding season (April–July), whereas the abundances of the other three species remained stable. Our data suggest that the foraging activities of birds in the intertidal zones of western North America are linked with the tidal cycles, corresponding to periods of high prey vulnerability.