The Mice That Roar . . . and the seabirds that die
by Mary Jane Schramm
Inside a deep crevice, a small, pearl-gray seabird, an Ashy storm-petrel, tended her single precious egg. She’d felt the small movements that signalled her chick was near hatching, all hungry peeps and fuzz. Waiting until nightfall to leave the tunnel’s safety to forage offshore, she jetted away from the island to elude the ever-watchful burrowing owls. But on this occasion speed failed her: she felt the twin grips of talons and of panic, and was dragged into the owl’s burrow. Thus, two members of a threatened species on an extinction trajectory were lost, mom and chick; oddly, because of a third, non-native species’ presence on the islands: the common house mouse, Mus musculus.
Wild Haven: The Farallon Islands National Wildlife Refuge hosts half the world’s population of Ashy storm-petrels, Oceanodroma homochroa, a species found exclusively on islands and rocky headlands along North America’s West Coast.
Going Native: After sealers first introduced mice to the islands in the early 1800s, followed by other destructive invasives, the Farallones went into an ecological tailspin. Some native wildlife nearly went extinct; many have still not recovered. But the US Fish and Wildlife Service, with Pt. Blue Conservation Science, have worked to restore them to their original state, especially its still-struggling seabird populations.
Plague Times: But massive numbers of house mice have infested the islands, 400-500 per acre, which have attracted the burrowing owls, Athene cunicularia, that kill hundreds of storm petrels annually. Gerry McChesney, Refuge Manager, explains: “The big impact on storm-petrels is from the relationship between mice, burrowing owls, and storm-petrels, resulting in hyper-predation on the storm-petrels. Owls arrive in fall migration at peak mouse abundance; several remain through the winter, feeding on mice. When the mouse population crashes in winter, owls switch to preying on storm-petrels, which are returning to the islands to begin courtship activities. Without the mice, the owls would not remain through winter, and this problem wouldn’t occur. The owls also prey extensively on the rare, endemic Farallon camel cricket, another indirect impact of house mice.”
Building On Success: Wildlife biologists have devised a permanent solution: only full eradication would break the vicious cycle. They modeled their plan on similar successful projects using rodenticides—rat and mouse poisons. These have now been Survivors may live only to endure famine again. Is this gruesome cycle kinder than eradicating them quickly and decisively to save a native seabird and other endemic wildlife?
Others advocate for birth control, even though untested on island ecosystems like the Farallones. Not even proponents claim the contraceptive will reach all the mice; many will continue to breed out of control. The Farallones would become a testing grounds for an unproven product. Even if partly successful, it would require repeated, wildlife-disrupting bait replenishment in sensitive habitats to treat the new mouse generations.
The Real Deal; And How To Help: Critics have spread misinformation and made misleading statements, especially concerning the amount of Brodifacoum involved. To read the rebuttals, learn the facts, and find out how you can help restore the Farallon Islands, see link [b] below).
Whatever you conclude, especially when considering complex issues such as this, always ponder both sides of an argument, and use critical thinking to guide your actions. Together we can help restore and protect our wild ocean planet.
LINKS:
[a] https://nmsfarallones.blob.core.windows.net/farallones-prod/media/archive/manage/pdf/sac/13_11/usfws_sefi.pdf
[b] https://www.pointblue.org/science_blog/farallon-islands-restoration-how-you-can-help/
[c] https://www.pressdemocrat.com/article/news/close-to-home-eradication-of-mice-on-farallon-islands-is-right-move/
NOTE:
With 400-500 mice per acre, the ground literally heaves and swells with their activity just beneath the surface, destroying native plants and seeds, rare endemic crickets, salamanders - and seabirds.
PHOTOS:
Top: "Ashy" at tunnel entrance, SE Farallon. Photo: USFWS
Above: Burrowing Owl courtesy Kevinsphotos from Pixabay.
