Data from: River otter predation of nesting seabirds along the coasts of North America

River otter (Lontra canadensis) predation of seabirds has been
periodically documented throughout North America, but most knowledge about
this subject exists as anecdotal observations in the memories of
experienced seabird biologists. Using surveys, interviews, white papers,
and published literature, we collected detailed records of seabird
predation by river otters at 73 islands on the coasts of North America.
From this dataset, we were able to conclude the seabird species
experiencing river otter predation, the geographic distribution of
predation records, and factors associated with river otter occurrence at
colony islands. River otters preferentially select for small-bodied
burrow-nesting species, with predation of ground-nesting species occurring
mostly opportunistically. 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. The presence of
burrow-nesting seabirds and proximity to the mainland are both strong
predictors of river otter occurrence at colony islands. River otters will
swim up to eight kilometers across open ocean to access seabird colonies,
but predation is significantly more common at nearshore islands (median
distance of 1.7km). Reports of seabird predation by river otters in
published literature are rare, heavily biased towards an ornithological
audience, and have decreased over time as “Field Notes” style publications
have decreased in popularity. Despite being more widespread than
previously reported, predation by river otters appears to be sustainable
for most colony nesting seabird populations.