During February and early March 2018, numerous live-stranded birds entered two wildlife care centers: The Society for the Prevention of Cruelty to Animals for Monterey (MSPCA) in Monterey County, California, US, and Pacific Wildlife Care (PWC) in San Luis Obispo County, California, US. Affected species included Northern Fulmars (Fulmarus glacialis), Common Murres (Uria aalge), and Cassin's Auklets (Ptychoramphus aleuticus). Some birds entering rehabilitative care exhibited opisthotonos, seizures, paresis, and ambulatory or locomotor deficits. Concurrent with this increased intake of live, sick birds, the Coastal Ocean Mammal and Bird Education and Research Surveys (BeachCOMBERS) program reported increased deposition of dead Common Murres, Northern Fulmars, and Cassin's Auklets on Monterey and San Luis Obispo County beaches. Blooms of toxigenic phytoplankton (Pseudo-nitzschia spp. and Alexandrium spp.) occurred in the same coastal regions (Monterey Bay and Morro Bay, California; R. Kudela pers. comm.) coincident with this mortality event. The counties in which birds were found is shown in Figure 1.

Figure1

Map showing the counties within the state of California, USA; Northern Fulmars (Fulmarus glacialis), Common Murres (Uria aalge), and Cassin's Auklets (Ptychoramphus aleuticus) were recovered in the coastal areas of Santa Cruz, Monterey, and San Luis Obispo counties during a 2018 mortality event.

Birds that died (n=4) or were euthanized (n=4) in rehabilitative care plus beachcast carcasses collected by biologists at the Oceano Dunes State Vehicular Recreation Area, California, (n=16) were submitted to the California Department of Fish and Wildlife–Marine Wildlife Veterinary Care and Research Center, Santa Cruz, California, US. These 24 necropsied birds (Northern Fulmars, n=16; Cassin's Auklets, n=4; Common Murres, n=4; Table 1) were from Monterey and San Luis Obispo counties. Histopathology was performed for selected Northern Fulmars only (n=7/24); tissues were fixed in 10% neutral buffered formalin, processed as described (Batac et al. 2020) and stained with H&E. Selected tissues were analyzed with Brown and Brenn stains to assess the characteristics of intralesional bacteria revealed by Gram staining.

Table 1

Seabirds examined during February and March 2018 from the Central California Coast, USA. Birds were determined to be unknown in sex or age class when the carcass was too decomposed for designation at gross postmortem examination.^a

The occurrence of an avian mass stranding event coincident with blooms of toxigenic phytoplankton prompted biochemical assessment of liver and kidney from stranded birds for the harmful algal bloom (HAB) toxins domoic acid (DA; n=8) and saxitoxin (STX; n=8) for four birds (two Common Murres and Northern Fulmars each; Table 2) at the University of California, Santa Cruz. Samples for biotoxin assessment were held at –20 C until processed, when 0.1–1.5 g of tissue was extracted in 50% methanol, cleaned with ISOLUTE SAX SPE columns (Biotage, Uppsala, Sweden) as described by Peacock et al. (2018), and analyzed with an Agilent 6130 liquid chromatography–mass spectrometry system (Agilent Technologies, Santa Clara, California, USA) and a Phenomenex Kinetex 2.6-µm 100 × 2.1-mm C18 column (Phenomenex, Torrance, California, USA). Domoic acid was quantified by peak area and retention time with the use of an external standard curve with Nuclear Regulatory Commission single-bond Canadian certified reference materials. Sample subsets were analyzed after standard addition of Nuclear Regulatory Commission single-bond Certified Reference Material DA to confirm peak identity and check for matrix effects. The method detection limit (MDL) was 0.30 ng/g for 1 g of tissue, with the MDL for specific samples dependent on sample weight.

Table 2

Domoic acid (DA) and saxitoxin (STX) results for representative seabirds examined during February and March 2018 from the Central California Coast, USA. The DA and STX results are also described in Gibble et al. (2021) with analytical details.

Samples assessed for STX were processed following the mussel extraction protocol provided by the manufacturer, with extracts stored at 4 C up to 1 wk, then diluted with diluent provided by Bioo Scientific and analyzed via the MaxSignal Saxitoxin (PSP) ELISA test kit (Bioo Scientific, Austin, Texas, USA). All samples, standards, and controls were plated in duplicate. A standard curve was fitted with a five-parameter logistic curve model and standard curve manufacturer-supplied matrix standards, per manufacturer protocols by the software provided with the plate reader (SoftMax Pro v5, Molecular Devices, San Jose, California, USA). The working range was determined by I20 and I80 values from the calibration curve to minimize errors in quantifying the signal. The I20 and I80 values are where 20% and 80% inhibition of the signal, respectively, is achieved; areas below and above those values are long tails in the curve, making for large errors in results.

All values over I80 were considered above the MDL, and values less than I20 were diluted further and rerun for accuracy. The MDL was 3.00 ng/g for 1 g of tissue; MDLs for individual samples varied by sample weight.

At postmortem examination, all Common Murres, Cassin's Auklets, and Northern Fulmars except individual 18-0235 were emaciated, with total depletion of subcutaneous and internal adipose, diffuse marked muscle atrophy, and empty gastrointestinal tracts (except animals fed while in care). All birds also had intestinal melena, indicative of prolonged stress (Selye 1973; Gelis 2005). Other than emaciation and melena, examined Cassin's Auklets and Common Murres had no significant gross pathology other than moderate diffuse congestion and jugular vein distension and enlarged adrenal glands for two Common Murres that stranded early in the event (individuals 18-0025 and 18-0026).

In contrast, all examined Northern Fulmars (n=16) had grossly apparent renal, ureteral, and cloacal pyogranulomas (Fig. 2). Affected ureters were distended and plugged by pale yellow to tan friable material, in some cases with secondary ureter rupture. Microscopic examination revealed severe pyogranulomatous and necrotizing pyelonephritis with intraepithelial protozoal macro- and microgamonts, schizonts, and lumenal oocysts (Figs. 3, 4). Also present were intralesional clusters of gram-negative bacterial rods, inspissated masses of necrotic epithelium and urate crystals, and perilesional multinucleated giant cells. On the basis of parasite morphology, size, and location, the protozoan was identified as Eimeria sp. The Eimeria sp. infection (i.e., renal coccidiosis or eimeriosis) was associated with epithelial hypertrophy, necrosis, sloughing, and partial obstruction and dilation of the collecting ducts and ureters (Fig. 3). Gram-negative bacterial proliferation (pyelonephritis) exacerbated this damage and further impaired renal and ureteral clearance, compounded by intralumenal urate deposition from dehydration.

Figure2

Gross pathology of urogenital system in frozen-thawed Northern Fulmars (Fulmarus glacialis) from a 2018 mortality event in central California, USA, showing multifocal irregular yellow-tan pyogranulomas in renal parenchyma and within markedly dilated, debris-filled ureters and the cloaca.

Figure3

Parasite- and bacteria-associated renal histopathology in frozen-thawed Northern Fulmars (Fulmarus glacialis) from a 2018 mortality event in central California, USA. A medullary collecting duct is effaced and obstructed by pyogranulomatous inflammation with intralesional clusters of bacterial rods (black arrowhead) and admixed Eimeria sp. oocysts (yellow arrowhead). The duct is partially ulcerated, with the lining epithelium replaced by a thick outer band of multinucleated giant cells (slender black arrows). H&E stain. Bar=45 µm.

Figure4

Parasite- and bacteria-associated pathology of caseonecrotic material from an obstructed and ruptured ureter in a Northern Fulmar (Fulmarus glacialis) from a 2018 mortality event in central California, USA, showing that the densely packed material is composed of numerous eosinophils and heterophils, necrotic cell debris, clusters of bacterial rods (black arrowhead), and admixed Eimeria sp. oocysts (yellow arrowhead). H&E stain. Bar=30 µm.

Biochemical test results provided additional insight. Domoic acid (0.00–20.973 ng/g) was detected in seven of eight samples (88%) from all four tested birds (Table 2). Saxitoxin (>MDL–20.946) was also detected in all eight samples from the four birds (Table 2). Domoic acid and STX were detected concurrently in 3/4 (75%), and 7/8 samples (88%; Table 2).

Wildlife health is often multifactorial, and fully understanding the related ecology of a mortality event requires significant resources. On the basis of all findings from postmortem examination and biochemical testing, all Common Murre and Cassin's Auklet deaths were attributed to emaciation, with HAB intoxication a potential contributing factor. Mortality events for seabirds attributed to emaciation are quite common, and prey availability and timing of food resources, adverse or extreme weather events, and other environmental anomalies may all contribute to these events (Newman et al. 2007, 2009; Jones et al. 2019; Diamond et al. 2020; Piatt et al. 2020), and findings of emaciation concurrent with secondary HAB interactions are consistent with other documented seabird wrecks (Gibble et al. 2018; Piatt et al. 2020; Van Hemert et al. 2020). In contrast, the Northern Fulmars were affected by multiple concurrent processes, including renal coccidiosis, bacterial pyelonephritis, dehydration with urate stasis, ureteral rupture, and emaciation. Although unconfirmed, concurrent HAB toxin exposure may have reduced the Northern Fulmars' resistance to renal coccidiosis, bacterial infection, or both. Emaciation also may have played a role by affecting resistance both to HAB exposure and to the infectious agents.

Eimeria spp.–associated renal coccidiosis has been reported from many avian genera (Nation and Wobeser 1977; Tuggle and Crites 1984; Leighton and Gajadhar 1986; Gajadhar and Leighton 1988; Yabsley et al. 2002). Pathogenicity varies from incidental infection to mass mortality due to parasite-associated nephropathy, characterized by epithelial hyperplasia, necrosis, sloughing, and tubular dilation (Tuggle and Crites 1984; Leighton and Gajadhar 1986; Yabsley et al. 2002; Morgan et al. 2013; Jankovsky et al. 2017). Eimeria spp. are the usual cause; these parasites are often taxon-specific and include many undescribed species. Infection occurs by consumption of sporocysts or sporulated oocysts shed in the urate fraction of avian feces. Parasites transmitted through oral-fecal exposure may be especially problematic for birds that are highly stressed by migration or use of crowded breeding and foraging areas (Rifkin et al. 2012). Biotoxin exposure may cause fatal intoxication or worsen the health effects from opportunistic parasites and bacteria.

Although fatal avian toxicosis has been reported, and lethal HAB doses have been

established experimentally for avian exposure to DA and STX, pathophysiologic and pharmacodynamic associations are underevaluated (Shumway et al. 2003; Gibble et al. 2021). Dusek et al. (2021) estimated the median oral lethal dose (LD₅₀) of STX in mallards (Anas platyrhynchos) as 167 µg/kg, and Silvagni (2003) established the intracoelomic LD₅₀ for DA as 900 µg/kg for pigeons (Columba livia), 4,000 µg/kg in mallards, and 4,100 µg/kg in Common Murres. However, intracoelomic toxin administration is not necessarily comparable to oral exposure. Although our DA and STX values (Table 2) are below the reported LD₅₀ for both toxins, they represent a single perimortem snapshot that does not account for rapid postexposure toxin clearance. Additionally, Silvagni (2003) demonstrated that LD₅₀ values can vary widely between avian species, and potential synergistic effects between HAB toxins and opportunistic pathogens are uncharacterized.

Our finding of concurrent renal coccidiosis, bacterial pyelonephritis, and HAB toxin exposure in Northern Fulmars illustrates how cascading comorbidities may exacerbate avian losses during mortality events. This compounding effect often underlies the detrimental effects of environmental degradation on seabird health. Although concurrent emaciation and DA intoxication have been noted previously during an avian mortality event (Gibble et al. 2018, 2021), emaciated birds are often not tested for HAB exposure because of the cost and limited laboratory availability and because the toxins are relatively ephemeral in avian tissues and gastrointestinal samples are often unavailable. However, recent studies demonstrating consistent HAB toxin detection in avian tissues (Van Hemert et al. 2020; Gibble et al. 2021) confirm the value of tissue screening for emaciated birds from mass strandings that coincide with HAB events. Without this testing, population-level HAB effects, risks from chronic sublethal toxin exposure and HAB-pathogen synergy, and emerging seabird health effects are likely to be missed. Continued investigation of mortality events is critical to optimize the collective understanding of coexisting threats for wildlife populations.

We thank all the staff and volunteers at The Society for the Prevention of Cruelty to Animals for Monterey, Pacific Wildlife Care, and Coastal Ocean Mammal and Bird Education and Research Surveys for their efforts to recover and document stranded seabirds. We also thank Jessie Beck for assistance with postmortem examinations, Kendra Negrey for University of California Santa Cruz Laboratory support, Chris Gardiner for parasite identification guidance, and Angelina Reed for final image formatting.

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