Chapter 22

Our observations tend to support the theory that colonization was by means of huge rafts of logs and debris…

Central Coast Islands 1939

Wandering Shrew

Wandering Shrew

[Vagrant Shrew] Sorex vagrans vagrans Photograph by Cowan. Image Cowan_PH_385 courtesy of University of Victoria Special Collections.
Northern Fur Seal

Northern Fur Seal

Callorhinus ursinus cynocephalus, Goose Island, 1939. Photograph by Cowan. Image Cowan_PH_361 courtesy of University of Victoria Special Collections.
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Cowan again seemed to have an uncanny ability to home in on interesting biodiversity and evolutionary hotspots. In 1939 these major archaeological and paleoecological discoveries were still 70 years away, so all he had to go on was local knowledge and the puzzle of the shrews. To that end he spent a lot of time watching where they foraged, what they ate and how they interacted with the sea. One account of July 13 was from Kwakshua:

Captured an immature shrew as it ran from a pile of seaweed 12' below high tide mark. Captured a second juvenile in a rock pit behind the cabin and saw a third escape into a burrow under a log. All these seen at mid-day and not later than 3 o’clock on a bright day without rain. One individual kept captive ate a small beetle, 3 earthworms, about a cubic centimetre of squirrel liver and yellow salmonberry in 12 hours. It died during the night.63

Cowan’s time with Thor Heyerdahl may have led him to theorize:

It is possible that certain of the islands were populated by glacier-transported debris containing small mammals… our observations tend to support the theory that colonization was by means of the huge rafts of logs and debris that annually slip from the precipitous and water-sodden hillsides and float out to sea.64

Cowan was on to something again. Insectivores have recently taken the limelight in their role in surviving another major global event – the mass extinction from the Chicxulub asteroid impact circa 66 million years ago, which wiped out the dinosaurs and everything else that wasn’t under a foot of soil or water. Humans have a lot to be grateful to shrews for — specifically our existence — because these early insectivores are the common ancestor from which all mammals repopulated the earth.65 They are one of the most ancient mammal groups with their fossils dating back 130 million years. Paleoecologists speculate that the ancestral shrew survived the temporary scorching of the asteroid impact by virtue of their shrewish disposition – preferring wet, marginal, subterranean, insect-rich environments. What is it about this group that enables them to disperse in hostile environments and through catastrophic events, whether fire or ice? Nagorsen writes, “The colonization of the numerous Pacific coastal islands by shrews remains one of the unexplained mysteries of island biogeography.”66


63 Cowan, “Species Index 1939–1942: Mammals,” P–Z, 27, Cowan_FN_016.

64 Cowan, “Insularity in the Genus Sorex,” 95–96.

65 John Alroy, “The Fossil Record of North American Mammals: Evidence for a Paleocene Evolutionary Radiation,” Systematic Biology 48, no. 1 (1999): 107–118. http://sysbio.oxfordjournals.org/content/48/1/107.full.pdf+html (full text accessed 2014-10-31).

66 Nagorsen, “Opossums, Shrews and Moles of British Columbia,” 28.

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