Shrews emerge in Riverside Park

Urban Ecology Center embraces new residents

When Jennifer Callaghan started her tenure at the Urban Ecology Center as an intern in 2006, her first assignment was to document shrews living in Riverside Park.

The problem: there were no shrews, which play an important role in ecosystems by keeping insect populations in check.

Monitoring over the past decade only revealed their continued absence from all of the Urban Ecology Center’s green spaces.

That is, until last month.

On the morning of July 18th, “a healthy, beautiful northern shorttail shrew crawled out of trap #3B and into our hearts. She pawed at her processing bag with her sweet pink feet and twitched her sizable pointed snout,” according to the Urban Ecology Center’s announcement.

“This project was my baby … It’s probably more exciting to me than it is to any other person because of the amount of work that’s gone into it,” said Callaghan, who is now the research and citizen science coordinator at the Urban Ecology Center.

Northern short-tailed shrews look similar to mice in shape and size, but they are not rodents. Instead, they are more closely related to moles and have velvety gray coats, tiny ears and a pointed snout. To compensate for their poor eyesight, these nocturnal animals use echolocation like bats and dolphins to navigate in the dark.

Additionally, mice are predominantly plant and seed eaters while shrews are insectivores. Their diet consists of meat supplied by invertebrates such as bugs, worms, slugs and spiders — and lots of them since their high metabolism can require more than their own weight in food per day.

According to Callaghan, northern shorttailed shrews are the most “hardcore” of all shrews because “they will actually take down other shrews” thanks to poison in their saliva that paralyzes prey. They are the only venomous shrew and one of the few mammals with this characteristic.

Milwaukee residents have nothing to fear from their new neighbor, though. These timid nighttime hunters are rarely encountered, and their bite, while unpleasant, can’t significantly harm a creature as large as a human.

Before the first shrew capture July 18 and a second Aug. 1, shrew populations had been identified on the other side of the Milwaukee River and along the river north of Locust St. So it seemed like only a matter of time before the shrew would appear in Riverside Park.

Caitlin Reinartz, an Urban Ecology land steward, said that restoration efforts to remove invasive plant species from Riverside Park and replace them with native Wisconsin plants could have encouraged shrews to move in.

Increasing the biodiversity of plants in the park encourages a higher diversity of insects. So where there used to be a small number of species for the shrew to eat, there’s now a “smorgasbord of insects out there,” she said.

Habitat fragmentation due to residential areas and other urban landscapes can also make migration for mammals difficult. “It’s really hard for a little shrew to cross a bunch of roads to get to a new habitat,” said Reinartz.

Connecting Riverside Park to other suitable areas such as those maintained by the River Revitalization Foundation and Milwaukee River Greenway Coalition has likely contributed to the shrews’ recent appearance.

Callaghan said that the park’s new tiny residents are particularly special because so many volunteers and staff have contributed to creating a welcoming environment for wildlife.

“It gives us validation that we’ve done a lot of work and that hard work is paying off,” she said.