Sunday, September 13, 2009
Yesterday I found the first nest of northern short-tailed shrews (Blarina brevicauda) I have ever found. I was transferring some straw from one pile to my compost pile, you know, the one that never reaches 170 degrees. Beneath the straw were two nests. One contained 4 or 5 babies, with gray fur and eyes still closed. I did not measure them, but I estimate that they were about 40mm in length, minus the tail. The other nest was empty and was about a foot from the babies' nest, but I am sure it was the nest for the mother. I had no idea that she kept a separate nest from her babies, but she was close enough to detect what was going on with them. I have captured this species in Sherman live traps many times, and I have watched the adults moving in the woods from time to time, but this was a novel event for me.
When I uncovered the nest, the babies began to scatter immediately. I quickly gathered them up and put them back in the nest. Shrews have a high metabolic rate, and I am sure these babies would die outside of the nest in short order, and it was a cool day. I returned about an hour later, and they were all gone. When I left them, they had been sleeping in the nest, all cuddled together (see photo). I am sure the female returned, realized that the site had been compromised, and moved them. She probably did this by picking each one up individually in her mouth, and moved them to a new location. I was unable to locate this new site.
Whitaker and Hamilton's "Mammals of the Eastern United States" give many details about the life history of this interesting mammal. This species feeds on numerous invertebrates, especially earthworms, slugs, and snails. They have been known to kill mice and even small birds. This species is one of only two shrews (and the only one in North America) with venomous saliva, and they are the only mammals in the world to have this feature, which they use to subdue their prey. The idea is that they are able to paralyze an earthworm and then place it in a food cache for later use; the food item does not die and decompose and yet is unable to crawl away. Young are born from early spring to late September, and a litter usually numbers 4-6. Copulation between male and female may last 25 minutes, with the pair locked together, and with the male seemingly inactive and dragged around by the female all the while. (No wise-crack comments, please. We are talking real biology here.) In addition, short-tailed shrews use echolocation (clicks in the range of 30-55 kHz) to navigate their environment, given their extremely small eyes and probable poor eyesight.
I have always maintained that there is still a great deal to learn about shrews and moles, given their relative secrecy and the difficulty observing them. I also tell students that no matter how much you have seen in nature, I can guarantee there is much more to be seen. I have been poking around fields and forests for 50 years, and the discovery of this nest taught me yet again that there is much I have to learn. So get out there and make a new discovery for yourself. And if you have children, take them with you. If you have a spouse, you can bring them also, as long as they leave their iPod, and cell phone, and any other electronic thingamabob at home. Cameras and binoculars are permitted, however.