The evidence: A very small number of adult bears with cubs went swimming. When the adult bears were next seen, maybe a year (or more?) later, less than half the cubs were missing. Conclusion: carbon dioxide caused the cubs to drown.
Eleven were mothers with cubs. In six cases, dependent cubs survived the swim when they were spotted again two months to a year later. But five cases, cubs could not be located after the long-distance swim.
USGS research zoologist George Durner said Tuesday that researchers cannot say for sure that the missing cubs drowned, but the evidence suggests long-distance swimming may be risky.
“For me, it raises my eyebrows to see the differences in mortality rates in cubs,” he said. “I wish we had better information to see when the mortality was actually occurring. That would give us a lot more information, but we don’t have that.”