River Otter Predation of Nesting Seabirds Along the Coasts of North America

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Seabirds are among the most threatened groups of birds, with anthropogenic impacts resulting in population declines for the majority of species.

“Seabirds are among the most threatened groups of birds, with anthropogenic impacts resulting in population declines for the majority of species (Croxall et al. 2012; Dias et al. 2019).”

• cites Croxall et al. 2012 sourcePartly supported

  The Status section says seabirds are more threatened than comparable bird groups, and the Threats section identifies several human-related pressures. The Trends section reports declines in 47% of all seabird species, or 52% of species with known trends. Thus, the claim's “majority of species” wording is supported only if limited to species with known trends; the paper does not establish that anthropogenic impacts caused every reported decline. Page numbers were not available in our copy. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites Dias et al. 2019 sourceDisputed

  The Introduction (p. 3) supports the statement that seabirds are among the most threatened groups of birds and identifies threats driving declines. But it reports declining population trends for 47% of species—almost half, not the claimed majority. (LLM, conf=0.88)

  Checked by a reasoning model — may be wrong.

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Arctic foxes and polar bears often overlap in habitat use with nesting seabirds at islands and mainland sites throughout the Arctic, where they will occasionally forage on eggs, chicks, and adult seabirds.

“For example, arctic foxes ( Vulpes lagopus ) (e.g., Larson 1960; Eide et al. 2005) and polar bears ( Ursus maritimus ) (e.g., Stempniewicz 1993; Dey et al. 2020) often overlap in habitat use with nesting seabirds at islands and mainland sites throughout the Arctic, where they will occasionally forage on eggs, chicks, and adult seabirds.”

• cites Larson 1960 sourceNot checked — no full text of the source
• cites Eide et al. 2005 sourceSupported
• cites Stempniewicz 1993 sourcePartly supported

  The opening passage (p. 1) says polar bears often visit Arctic islands with seabird colonies. The paper’s summary (p. 1) and Observations (p. 2) document bears eating little auk eggs, chicks, and adults at one island colony. It does not establish the polar-bear claim for mainland sites throughout the Arctic. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

Classified as probably not a substantial claim.

The damaging effects of introduced predators on nesting seabirds at offshore colony islands has led to an implicit assumption in much of the published literature that terrestrial carnivores and colonial seabirds cannot coexist.

“The damaging effects of introduced predators on nesting seabirds at offshore colony islands has led to an implicit assumption in much of the published literature that terrestrial carnivores and colonial seabirds cannot coexist (Courchamp et al. 2003; Hays and Conant 2007; Croxall et al. 2012; Nogales et al. 2013).”

• cites Courchamp et al. 2003 sourceNot checked — no full text of the source
• cites Hays and Conant 2007 sourcePartly supported

  The “Impact on Bird Populations” section reports probable mongoose-driven extinction of the Jamaica petrel and evidence of predation on Hawaiian petrels. It does not discuss offshore colony islands or say that the published literature assumes terrestrial carnivores and colonial seabirds cannot coexist; it also describes some ground-nesting birds persisting alongside mongooses. Page numbers were not available in our copy. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites Croxall et al. 2012 sourcePartly supported

  The Threats section (page not provided) identifies invasive species at breeding sites as a major threat to seabirds, supporting the claim about damaging effects. It does not say that published literature assumes terrestrial carnivores and colonial seabirds cannot coexist, or that predator impacts led to such an assumption. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

Studies of river otter foraging strategies in primary freshwater habitats have shown that river otters consistently select for larger-bodied fish within individual taxa.

“This result initially appears to contrast with studies of river otter foraging strategies in their primary freshwater habitats, where river otters have been shown to consistently select for larger‐bodied fish within individual taxa (Hansen 2003; Cote et al. 2008).”

• cites Hansen 2003Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Cote et al. 2008 sourcePartly supported

  The Results report that larger individuals of each fish taxon were more common in otter scats than in samples of available fish. But this study examined marine-coastal habitats in Newfoundland, not primary freshwater habitats, so it does not establish the claim about freshwater studies. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

Almost all seabird species have low reproductive rates and long lifespans, and these traits amplify the effects of additive sources of mortality on long-term population trajectories.

“Almost all seabird species have low reproductive rates and long lifespans (Hamer et al. 2001), and these traits amplify the effects of additive sources of mortality on long‐term population trajectories (Purvis et al. 2000; Sæther and Bakke 2000).”

• cites Hamer et al. 2001Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Purvis et al. 2000 sourceSupported
• cites Sæther and Bakke 2000 sourceNot checked — no full text of the source

May combine two claims.

River otter predation of nesting seabirds occurs on both coasts of North America, with some records indicating the predation of hundreds of nesting seabirds from a single colony.

“Regardless, this behavior occurs on both coasts of North America, with some records indicating the predation of hundreds of nesting seabirds from a single colony (e.g., Quinlan 1983; Hoeg et al. 2021).”

• cites Quinlan 1983 sourceNot checked — no full text of the source
• cites Hoeg et al. 2021 sourcePartly supported

  The study-site description (p. 120) says river otters have appeared at the two Nova Scotia colonies and have killed Leach’s Storm Petrels. The Abstract estimates 4,000 petrels depredated annually at one colony, but does not attribute those deaths to otters; most identified predation was by gulls or owls. Hoeg et al. therefore supports otter predation on the Atlantic coast, not hundreds of seabirds killed by otters at a single colony. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

Even in locations where predation does not cause serious reductions in population, the presence of native predators can result in shifts in nest attendance, changes to socialization and breeding behavior, and costly physiological stress responses.

“Even in locations where predation does not cause serious reductions in population, the presence of native predators can result in shifts in nest attendance (Corkery et al. 2015; Marsteller et al. 2024), changes to socialization and breeding behavior (Mougeot and Bretagnolle 2000), and costly physiological stress responses (Schaefer and Colombelli‐Négrel 2021; Geldart et al. 2023).”

• cites Corkery et al. 2015 sourceSupported
• cites Marsteller et al. 2024 sourceSupported
• cites Mougeot and Bretagnolle 2000 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Seabird predation by invasive American mink has received extensive attention in Europe, but this has not been the subject of a comprehensive review in North America.

“Seabird predation by invasive American mink has received extensive attention in Europe (Craik 1997; Banks et al. 2008), but this has not been the subject of a comprehensive review in North America.”

• cites Craik 1997 sourceSupported
• cites Banks et al. 2008Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

River otters generally select for benthic, slow-moving aquatic prey available in high abundance, suggesting that they rely on a "risk averse" foraging strategy that focuses on consistently catchable prey rather than targeting species that might provide a greater energetic reward per capture.

“River otters generally select for benthic, slow‐moving aquatic prey available in high abundance (Ryder 1955; Cote et al. 2008; Day et al. 2015), suggesting that they rely on a “risk averse” foraging strategy that focuses on consistently catchable prey rather than targeting species that might provide a greater energetic reward per capture (Pyke 1984).”

• cites Ryder 1955 sourceNot checked — no full text of the source
• cites Cote et al. 2008 sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured
• cites Day et al. 2015 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

The role of terrestrial mammals in coastal systems has generally been understudied.

“The role of terrestrial mammals in coastal systems has generally been understudied (Carlton and Hodder 2003), and the anecdotal knowledge of seabird biologists on a suite of native terrestrial species remains an underexplored scientific resource.”

• cites Carlton and Hodder 2003 sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Reports of seabird predation by river otters in published literature have decreased over time as "Field Notes" style publications have decreased in popularity.

“Reports of seabird predation by river otters in published literature are rare, are heavily biased toward an ornithological audience, and have decreased over time as “Field Notes” style publications have decreased in popularity.”

May combine two claims.

The presence of burrow-nesting seabirds and proximity to the mainland are both strong predictors of river otter occurrence at colony islands.

“The presence of burrow‐nesting seabirds and proximity to the mainland are both strong predictors of river otter occurrence at colony islands.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

Predation of nesting seabirds by river otters occurs across the entire Pacific range of the river otter and throughout the northern Atlantic.

“Predation of nesting seabirds occurs across the entire Pacific range of the river otter and throughout the northern Atlantic, but we did not locate a single record of this behavior on the Atlantic coast south of Maine; we hypothesize that this is due to geographic differences in nesting seabird assemblages.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

River otters preferentially select for small-bodied burrow-nesting species, with predation of ground-nesting species occurring mostly opportunistically.

“River otters preferentially select for small‐bodied burrow‐nesting species, with predation of ground‐nesting species occurring mostly opportunistically.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

Probably not a substantial claim: may not pass S3 (load-bearing).

Reports of seabird predation by river otters in published literature are heavily biased toward an ornithological audience.

“Reports of seabird predation by river otters in published literature are rare, are heavily biased toward an ornithological audience, and have decreased over time as “Field Notes” style publications have decreased in popularity.”

May combine two claims.

River otter predation of burrow-nesting species was reported to be fairly common, but the specific mode of predation varied.

“While river otter predation of burrow‐nesting species was reported to be fairly common, the specific mode of predation varied.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

Probably not a substantial claim: may not pass S3 (load-bearing).

Four surveyed biologists suggested river otters would be unable or unwilling to swim more than 500 m to access a seabird colony island.

“four biologists suggested that river otters would be unable or unwilling to swim more than 500 m to access a seabird colony island”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The survey received responses from 16 of 24 river otter biologists throughout North America, who collectively have authorship on 92 unique publications about river otter ecology.

“We distributed surveys to 24 river otter biologists throughout North America, and we received responses from 16 of these biologists, who collectively have authorship on 92 unique publications about river otter ecology.”

May combine two claims.

At many sites, river otters were reported to consistently use specific access paths onto the islands and developed well-established trails.

“At many of these sites, river otters were reported to consistently use specific access paths onto the islands and developed well‐established trails.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

In most cases where river otters were not living full-time on the island, river otters made repeated visits to the colony throughout the breeding season to depredate seabirds; one-off instances of predation seem to be quite rare.

“In most cases where river otters were not living full‐time on the island, however, river otters made repeated visits to the colony throughout the breeding season to depredate seabirds; one‐off instances of predation seem to be quite rare.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

Probably not a substantial claim: may not pass S3 (load-bearing).

Five surveyed biologists predicted the upper threshold for river otter swim distance to seabird colony islands would be between five and ten kilometers.

“five other biologists predicted (remarkably accurately) that the upper threshold for this distance would be between five and ten kilometers.”

May combine two claims.

After accounting for abundance and body mass, river otters show a strong preference for burrow-nesting species over all other types of nesters; with body mass and abundance held constant, burrow nesters have 2.8 times higher odds of being depredated than surface nesters, though the uncertainty around this odds ratio is broad (95% CI: [1.3×, 6.4×]).

“After accounting for abundance and body mass, river otters show a strong preference for burrow‐nesting species over all other types of nesters; with body mass and abundance held constant, burrow nesters have 2.8 times higher odds of being depredated than surface nesters, though the uncertainty around this odds ratio is broad (95% CI: [1.3×, 6.4×]).”

May combine two claims.

Many of the contacted biologists had decades of field experience working with nesting seabirds, and not a single individual spoken with had ever observed river otter predation in these areas.

“Many of these biologists had decades of field experience working with nesting seabirds, and not a single individual we spoke with had ever observed river otter predation in these areas.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

Of the 22 publications, 13 were secondary anecdotal mentions, six were field-note style publications, and three were primary field research on river otter predation of nesting seabirds.

“Thirteen of these were secondary anecdotal mentions (often just a single sentence) in seabird population studies, six were “field note” style publications, and in just three instances was river otter predation of nesting seabirds an intentional subject of primary field research (Verbeek and Morgan 1978; Quinlan 1983; Carter et al. 2012).”

• cites Verbeek and Morgan 1978 sourceNot checked — no full text of the source
• cites Quinlan 1983 sourceNot checked — no full text of the source
• cites Carter et al. 2012Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

The amount of writing on seabird predation by river otters has clearly declined, associated with the progressive disappearance of field-note style publications in journals.

“While many of these records were published in the last twenty years, the progressive disappearance of “field note” style publications in journals has resulted in a clear decline in the amount of writing on this subject (Figure 4).”

May combine two claims.

The authors gathered records of river otter and American mink overlap for sites in Alaska, British Columbia, Oregon, Newfoundland, Nova Scotia, and Maine-with many seabird biologists reporting that mink were a more important management issue than river otters.

“We gathered records of this overlap for sites in Alaska, British Columbia, Oregon, Newfoundland, Nova Scotia, and Maine—with many seabird biologists reporting that mink were a more important management issue than river otters.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

The authors collected just 6 records of river otters hunting seabirds at colonies lacking burrow nesters, with all of these observations from river otters hunting glaucous-winged gulls in the Salish Sea of British Columbia and Washington.

“We collected just 6 records of river otters hunting seabirds at colonies lacking burrow nesters, with all of these observations from river otters hunting glaucous‐winged gulls in the Salish Sea of British Columbia and Washington (Figure 3b).”

Probably not a substantial claim: may not pass S3 (load-bearing).

River otter biologists generally agreed that seabird predation would not be dramatically outside their expectations, despite river otters' typical niche as aquatic predators.

“Despite this absence of reported observations, river otter biologists generally agreed with the notion that seabird predation would not be dramatically outside their expectations, despite river otters' typical niche as aquatic predators.”

May combine two claims.

Nine of the references came from ornithological journals and another nine came from regionally restricted natural history journals.

“Additionally, nine of these references came from ornithological journals, while another nine came from regionally restricted natural history journals.”

May combine two claims.

Biologists from both Rhode Island and Georgia reported that while river otters never depredate nesting seabirds despite their presence in the area, mink are active predators at these sites.

“Biologists from both Rhode Island and Georgia reported that while river otters never depredate nesting seabirds despite their presence in the area, mink are active predators at these sites.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

The authors collected multiple records of river otter activity at seabird colony islands in both Massachusetts and South Carolina, but predation was not observed at any of these sites.

“We did collect multiple records of river otter activity at seabird colony islands in both Massachusetts and South Carolina, but predation was not observed at any of these sites.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

Probably not a substantial claim: may not pass S3 (load-bearing).

Six surveyed biologists referenced river otter predation on rafting and nesting waterfowl.

“In their comments, six different biologists made reference to river otter predation on rafting and nesting waterfowl, and these biologists suggested that such behavior would likely translate to a coastal context.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Those biologists suggested that river otter predation on waterfowl would likely translate to a coastal context.

“In their comments, six different biologists made reference to river otter predation on rafting and nesting waterfowl, and these biologists suggested that such behavior would likely translate to a coastal context.”

May combine two claims.

The presence of burrow-nesting species was very strongly associated with river otter occurrence; the top model predicted that the odds of river otter activity are 19.7× higher for islands with burrow-nesting species (95% odds ratio CI: [7.4×, 60.8×], p < 0.001), though effect sizes estimated from such a highly skewed sample should be interpreted with caution.

“The presence of burrow‐nesting species was very strongly associated with river otter occurrence; our top model predicted that the odds of river otter activity are 19.7× higher for islands with burrow‐nesting species (95% odds ratio CI: [7.4×, 60.8×], (p < 0.001)), though effect sizes estimated from such a highly skewed sample should be interpreted with caution.”

May combine two claims.

At many other storm-petrel colonies where river otter predation was fairly well observed, burrow excavation never occurred, and river otters exclusively killed adult birds outside of their burrows.

“At many other storm‐petrel colonies where river otter predation was fairly well observed, burrow excavation never occurred, and river otters exclusively killed adult birds outside of their burrows.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

When hunting larger surface-nesting species such as gulls, predation of both chicks and eggs seems to be relatively common, despite previous reports that river otters avoid consuming bird eggs.

“When hunting larger surface‐nesting species such as gulls, predation of both chicks and eggs seems to be relatively common (see Rodway et al. 2024 for examples), despite previous reports that river otters avoid consuming bird eggs (Hansen 2003).”

• cites Rodway et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Hansen 2003Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

At one site in British Columbia, river otters regularly entered artificial nest boxes to depredate pigeon guillemots, but this was effectively prevented by later reducing the diameter of nest box entrances.

“At one site in British Columbia, river otters regularly entered artificial nest boxes to depredate pigeon guillemots, but this was effectively prevented by later reducing the diameter of nest box entrances.”

• AssumptionRests on an assumption: Biologists' anecdotal reports of river otter activity and predation are accurate enough to use as data.

May combine two claims.

Seabird predation by river otters appears to be most common in the North Pacific (41% of records are from British Columbia), but this behavior occurs throughout the Pacific coast and in the northern Atlantic.

“Seabird predation by river otters appears to be most common in the North Pacific (41% of our records are from British Columbia), but this behavior occurs throughout the Pacific coast and in the northern Atlantic (Figure 1).”

May combine two claims.

The authors acquired full species abundance data for 79 of these islands, resulting in a final model dataset with a total sample size of 377 nesting records across 30 different seabird species.

“We were able to acquire full species abundance data for 79 of these islands, resulting in a final model dataset with a total sample size of 377 nesting records across 30 different seabird species.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

It superficially appears that permanent or extended seasonal residence was more common on islands with sources of persistent freshwater, but the authors do not have sufficient data to quantitatively assess this.

“It superficially appears that permanent or extended seasonal residence was more common on islands with sources of persistent freshwater, but we do not have sufficient data on river otter residence patterns to quantitatively assess this.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Some anecdotal records report river otters scaling remarkably steep cliffs to access nesting areas, but it is logical that these predators would concentrate their foraging efforts on seabirds inhabiting flat areas of colony islands.

“Some anecdotal records report river otters scaling remarkably steep cliffs to access nesting areas, but it is logical that these predators would concentrate their foraging efforts on seabirds inhabiting flat areas of colony islands.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Many anecdotal reports describe a similar pattern of river otters making nightly trips to seabird colony islands.

“many anecdotal reports we received describe a similar pattern.”

May combine two claims.

River otters coexist with seabirds at many sites in North America without exhibiting any predatory tendencies, instead using the coasts of seabird islands as foraging grounds for their typical marine prey.

“River otters coexist with seabirds at many sites in North America without exhibiting any predatory tendencies, instead using the coasts of seabird islands as foraging grounds for their typical marine prey (Rodway et al. 2020).”

• cites Rodway et al. 2020Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Through the course of this project, the authors spoke with over fifty active seabird biologists who have documented seabird predation by river otters, but there have been just 306 words published on the subject in the last decade.

“Through the course of this project, we spoke with over fifty active seabird biologists who have documented seabird predation by river otters, but there have been just 306 words published on the subject in the last decade.”

May combine two claims.

Seabird biologists seem to observe predation by river otters fairly frequently, but they very rarely study river otter behavior in a targeted manner or include their observations in publications.

“Seabird biologists seem to observe predation by river otters fairly frequently, but they very rarely study river otter behavior in a targeted manner or include their observations in publications.”

May combine two claims.

There are very few references to river otter predation of nesting seabirds in the literature, particularly in wildlife management journals, yet it is a fairly common occurrence in areas with large populations of burrow-nesting seabirds.

“There are very few references to this species interaction in the literature (particularly in wildlife management journals), yet it is a fairly common occurrence in areas with large populations of burrow‐nesting seabirds.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The authors received many anecdotal reports of river otters hunting much larger species on the water, including murres, cormorants, and pelicans.

“While successfully killing large seabirds on land may be challenging for river otters, we received many anecdotal reports of river otters hunting much larger species on the water, including murres, cormorants, and pelicans.”

May combine two claims.

The Salish Sea is the only known location in the world where river otters have been consistently observed to visit islands to exclusively hunt a surface-nesting species (glaucous-winged gulls), with local reports for at least the last 60 years.

“The Salish Sea is the only known location in the world where river otters have been consistently observed to visit islands to exclusively hunt a surface‐nesting species (glaucous‐winged gulls), and there have been local reports of this behavior for at least the last 60 years (Kennedy 1968; Rodway et al. 2024).”

• cites Kennedy 1968Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Rodway et al. 2024Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Our modeling did not show any convincing evidence that island size or the presence of persistent freshwater increase the likelihood of river otters accessing a seabird colony island.

“Our modeling did not show any convincing evidence that island size or the presence of persistent freshwater increase the likelihood of river otters accessing a seabird colony island.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Very few seabird biologists who had direct experience with river otter predation suggested that river otters represented a serious threat to the future of the colonies they study.

“That being said, very few seabird biologists who had direct experience with river otter predation suggested that river otters represented a serious threat to the future of the colonies they study.”

Classified as probably not a substantial claim. May combine two claims.

The management of river otters in the United States typically falls under the purview of furbearer biologists working for state wildlife agencies, but the survey work suggests that this population has limited information about the behavior of river otters at coastal islands.

“The management of river otters in the United States typically falls under the purview of furbearer biologists working for state wildlife agencies, but our survey work suggests that this population has limited information about the behavior of river otters at coastal islands.”

May combine two claims.

In these cases, river otters swam underwater and attacked seabirds from below, restraining their legs in their jaws and drowning them before returning to shore to consume the carcass.

“In these cases, river otters swam underwater and attacked seabirds from below, restraining their legs in their jaws and drowning them before returning to shore to consume the carcass—a very similar strategy that has been observed on freshwater lakes where river otters hunt waterfowl (Reid et al. 1994; Price and Aries 2007).”

May combine two claims.

Biologists reported high rates of predation on storm-petrels with limited or no evidence of burrow excavation, suggesting river otters often hunt adult birds on the ground outside of burrows.

“In many cases, however, biologists reported high rates of predation on storm‐petrels with limited or no evidence of burrow excavation—suggesting that river otters often hunt adult birds on the ground outside of burrows.”

May combine two claims.

Most journal articles mentioning seabird predation by river otters were from specialist or local journals, and very few articles mention the subject in their abstract.

“Most journal articles mentioning seabird predation by river otters were from specialist or local journals, and very few articles mention the subject in their abstract.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

River otter biologists that were surveyed anticipated the ability of river otters to adapt to hunt seabirds in a coastal context, but they generally seemed to underestimate how valuable a foraging opportunity a densely nested seabird colony represents.

“River otter biologists that we surveyed anticipated the ability of river otters to adapt to hunt seabirds in a coastal context, but they generally seemed to underestimate how valuable a foraging opportunity a densely nested seabird colony represents.”

May combine two claims.

Almost the entirety of existing knowledge on seabird predation by river otters seems to lie with seabird biologists; there are no notable publications on the subject by river otter biologists, and the authors did not obtain any new records of seabird predation from the river otter biologists they interviewed.

“Almost the entirety of existing knowledge on seabird predation by river otters seems to lie with seabird biologists; there are no notable publications on the subject by river otter biologists, and we did not obtain any new records of seabird predation from the river otter biologists we interviewed.”

May combine two claims.

In general, publications mentioning this behavior are sparse, declining in frequency, and difficult to opportunistically discover.

“In general, publications mentioning this behavior are sparse, declining in frequency, and difficult to opportunistically discover.”

Probably not a substantial claim: may not pass S1 (asserted), S4 (based).

The absence of river otter predation records on the Atlantic coast south of Maine is due to geographic differences in nesting seabird assemblages.

“we hypothesize that this is due to geographic differences in nesting seabird assemblages”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Many estimates of seabird abundance for the islands were more than two decades old, but the authors used the newest available data wherever possible.

“It should be noted that many estimates of seabird abundance for these islands were more than two decades old, but we used the newest available data wherever possible.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

River otters readily forage on marine resources, and coastal areas can have higher population densities than freshwater habitats.

“Despite the implications of their common name, river otters readily forage on marine resources, and coastal areas can have higher population densities than freshwater habitats (Blundell et al. 2000).”

• cites Blundell et al. 2000Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Classified as probably not a substantial claim.

The authors asked seabird biologists to report the number of years and weeks per year spent conducting field research on the island to determine whether detections of river otter activity were biased by monitoring intensity.

“We also asked seabird biologists to report the number of years and weeks per year that they spent conducting field research on the island to determine whether detections of river otter activity were biased by monitoring intensity.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The authors used an all-subsets model selection approach with AICc as selection criteria to account for limited sample size.

“We used an all‐subsets model selection approach (due to the small model set), with Akaike's Corrected Information Criterion (AICc) as our selection criteria to account for our limited sample size (Hurvich and Tsai 1989).”

• cites Hurvich and Tsai 1989 sourceNot checked — no full text of the source

Classified as probably not a substantial claim.

To ensure that the absence of predation records was not due to geographic bias in survey distribution channels, the authors directly reached out to over twenty state, federal, academic, and nonprofit biologists working throughout the region.

“To ensure that this absence of predation records was not due to geographic bias in our survey distribution channels, we directly reached out to over twenty state, federal, academic, and nonprofit biologists working throughout this region.”

May combine two claims.

Due to the mixed sampling approach, the reported outcomes are positively biased towards the overrepresentation of river otter activity, and the dataset cannot be used to estimate the exact probability of river otters occurring at seabird colony islands.

“Due to our mixed sampling approach, our reported outcomes are positively biased towards the overrepresentation of river otter activity, and this dataset cannot be used to estimate the exact probability of river otters occurring at seabird colony islands.”

Classified as probably not a substantial claim. May combine two claims.

River otters primarily hunt fish and crustaceans, but their dietary composition generally tracks the abundance of available prey, and they have been observed to take large amounts of amphibians, mammals, and birds in specific circumstances.

“River otters primarily hunt fish and crustaceans, but their dietary composition generally tracks the abundance of available prey, and they have been observed to take large amounts of amphibians, mammals, and birds in specific circumstances (Kruuk 2006).”

• cites Kruuk 2006 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

The true magnitude of the distance effect may be masked by seabirds actively selecting against nesting on islands very close to shore (within 2 km) due to high threat of predation by native terrestrial mammals.

“the true magnitude of this distance effect may be masked by the fact that seabirds could be actively selecting against nesting on islands that are very close to shore (within 2 km) due to the high threat of predation by native terrestrial mammals.”

Probably not a substantial claim: may not pass S2 (checkable).

This project highlights the importance of drawing on the knowledge of taxa-specific experts to understand the behavior of certain species at the edge of their typical niche.

“Perhaps more than anything, this project highlights the importance of drawing on the knowledge of taxa‐specific experts to understand the behavior of certain species at the edge of their typical niche.”

Probably not a substantial claim: may not pass S2 (checkable).

River otters have been underacknowledged as a native predator of nesting seabirds throughout North America.

“River otters have been underacknowledged as a native predator of nesting seabirds throughout North America.”

May combine two claims.

This suggests that specialized seabird predation can be a locally learned and socially transmitted behavior, enabling certain populations to use an alternative prey resource.

“This suggests that specialized seabird predation can be a locally learned and socially transmitted behavior, enabling certain populations to use an alternative prey resource.”

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

The anecdotal knowledge of seabird biologists on a suite of native terrestrial species remains an underexplored scientific resource.

“the anecdotal knowledge of seabird biologists on a suite of native terrestrial species remains an underexplored scientific resource.”

Probably not a substantial claim: may not pass S2 (checkable), S4 (based). May combine two claims.

These preferred prey species likely have a higher capture rate and require less energy to hunt, making it more likely for river otters to behaviorally adapt to include seabirds in their diet.

“These preferred prey species likely have a higher capture rate and require less energy to hunt, making it more likely for river otters to behaviorally adapt to include seabirds in their diet.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Prey response may also partially explain the lack of preference for nocturnally provisioning seabirds-if predator vigilance is reduced in diurnal species during the night, hunting success rates for nocturnally hunting river otters would be comparatively increased.

“Prey response may also partially explain the lack of preference for nocturnally provisioning seabirds—if predator vigilance is reduced in diurnal species during the night, hunting success rates for nocturnally hunting river otters would be comparatively increased.”

Classified as probably not a substantial claim.

Due to the nocturnal behavior of otters and their typically transient appearance at islands, diagnosing them as a source of predation can be difficult-particularly when islands are only visited for periodic censuses of seabird populations.

“Due to the nocturnal behavior of otters and their typically transient appearance at islands, diagnosing them as a source of predation can be difficult—particularly when islands are only visited for periodic censuses of seabird populations.”

May combine two claims.

While river otters will take larger-bodied surface-nesting species, the anecdotal reports collected suggest this is primarily an opportunistic behavior exhibited at islands with an abundance of preferred prey.

“While river otters will take larger‐bodied surface‐nesting species, the anecdotal reports we collected suggest that this is primarily an opportunistic behavior exhibited at islands with an abundance of preferred prey.”

Probably not a substantial claim: may not pass S1 (asserted).

The stark geographic split in the occurrence of predation is primarily the result of species assemblages at seabird islands on the Atlantic coast.

“Instead, we hypothesize that this stark geographic split in the occurrence of predation is primarily the result of species assemblages at seabird islands on the Atlantic coast.”

May combine two claims.

Locomotion and foraging may be more challenging in boulder fields and rocky scree than in flat vegetated areas, and guillemots at many islands will congregate on steep cliffs that may be fully inaccessible to river otters.

“Locomotion and foraging may be more challenging in boulder fields and rocky scree than in flat vegetated areas, and guillemots at many islands will congregate on steep cliffs that may be fully inaccessible to river otters (Oakley 1981).”

• cites Oakley 1981Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing). May combine two claims.

Seabird colonies represent a habitat at the very edge of a river otter's niche, and they provide a unique insight into the extreme adaptability of this generalist predator.

“Seabird colonies represent a habitat at the very edge of a river otter's niche, and they provide a unique insight into the extreme adaptability of this generalist predator.”

May combine two claims.

This could allow for sustained foraging on burrow-nesting species, whereas making repeated kills on surface nesters during a single hunting bout seems more unlikely.

“This could allow for sustained foraging on burrow‐nesting species, whereas making repeated kills on surface nesters during a single hunting bout seems more unlikely.”

May combine two claims.

The only burrow-nesting species with colonies on the Atlantic coast are Leach's storm-petrels and Atlantic puffins, and the most southern major colony of either is located in St. George, Maine.

“The only burrow‐nesting species with colonies on the Atlantic coast are Leach's storm‐petrels and Atlantic puffins, and the most southern major colony of either of these species is located in St. George, Maine (Lowther et al. 2020; Pollet et al. 2021).”

• cites Lowther et al. 2020Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Pollet et al. 2021 sourceNot checked — no full text of the source

May combine two claims.

The absence of seabird predation south of Maine may be partially due to a lower density of both seabird colonies and coastal river otters in the region, but this seems an insufficient explanation for the complete absence.

“This may be partially due to a lower density of both seabird colonies and coastal river otters in the region (compared to the Pacific coast and northern Atlantic), but this seems to be an insufficient explanation for the complete absence of any observed seabird predation.”

May combine two claims.

Collective vigilance is likely further limited during incubation when adults remain in their burrows for much of the day, and adults are unlikely to collectively flush from their burrows in response to a single predation attempt.

“Collective vigilance is likely further limited during incubation when adults remain in their burrows for much of the day, and adults are unlikely to collectively flush from their burrows in response to a single predation attempt.”

• AssumptionRests on an assumption: Burrow-nesting species have not been shown to demonstrate coordinated group responses to terrestrial predators.

May combine two claims.

It appears that while gulls, terns, and murres may be suitable prey, it is not possible for river otters in most areas to become efficient enough hunters of surface nesters for them to become a primary prey item.

“It appears that while gulls, terns, and murres may be suitable prey, it is not possible for river otters in most areas to become efficient enough hunters of surface nesters for them to become a primary prey item.”

May combine two claims.

While river otters will opportunistically take surface-nesting seabirds in areas with dense burrow-nesting colonies, the species assemblages south of Maine do not offer a valuable enough food resource for river otters to specialize as seabird predators.

“While river otters will opportunistically take surface‐nesting seabirds in areas with dense burrow‐nesting colonies, it appears that the species assemblages south of Maine do not offer a valuable enough food resource for river otters to specialize as seabird predators.”