Regular readers of this website know that we’ve been following the Natural Areas Programs attempts to reintroduce the Mission Blue Butterfly to Twin Peaks. We’ve just obtained the latest report from San Francisco Recreation and Parks Dept (SFRPD). It’s very mixed.
(The whole report is here as a PDF. Mission Blue Butterfly response- ProgressReportNov2012)
[Edited to Add (June 17, 2013): There’s better news in 2013. Scroll down to the bottom to read about it.]
THE STORY SO FAR
San Francisco Recreation and Parks Department (SFRPD) through its Natural Areas Program (NAP) is trying to reintroduce the Mission Blue Butterfly to Twin Peaks by transplanting them from San Bruno Mountain, where a natural population still flies. After planting Twin Peaks with the nursery plant, lupine, in 2008, they began moving butterflies in 2009.
We have a more detailed account and analysis HERE, but here it is in brief:
- In 2009, they moved 22 female butterflies to Twin Peaks and caged them over lupine plants until they laid their eggs. They hoped the butterflies would go forth and multiply. Only a small number made it.
- In 2010, NAP observers counted 14 larvae, and 17 adult butterflies. This was not a self-sustaining population.
- In 2011, they spotted only 3 larvae and 7 adults, of which two were females. So they got US Fish and Wildlife Service permits to take more butterflies from San Bruno Mountain – 40 females and 20 males – which they released in May 2011.
WHAT HAPPENED IN 2012
Unfortunately, the larger release didn’t really seem to pay off. The survey in the first few months of 2012 showed only 6 larvae and 7 adults (of which one was female). This may have been because 2012 was a bad Mission Blue year all round. So bad, in fact, that they could not get 60 new butterflies from San Bruno Mountain to release, (though they had a US Fish and Wildlife Service permit to move 40 females and 20 males). They only moved 16 butterflies, of which 11 were females.
Nevertheless, the butterflies do seem to have laid a decent number of eggs. Observers counted 273 of them. That’s nearly as many as the 295 they found after the big 60-butterfly move in 2011. So there’s hope yet.
HOW MUCH HOPE?
How much hope, we don’t know. How many of the 273 eggs will complete the maturation to butterflies? Probably no more than 10-15%. In addition to normal predation, conditions on Twin Peaks may not be optimal.
- Mission Blue caterpillars are guarded by ants, which are attracted to them by honeydew, a sweet excretion. They reduce predation on the caterpillars by other insects. But we don’t know if Twin Peaks has the right ant populations or not.
- In an attempt to encourage native plants in general and lupine in particular, NAP regularly sprays Twin Peaks with pesticides (17 times in 2012, according to pesticide records we obtained under the Sunshine Act). This could have an adverse effect on the caterpillars. A study on metalmark butterflies showed three pesticides gave a 24-36% reduction in the number of caterpillars making it to the pupa stage. We don’t know if it would be the same for Mission Blues. (Chris Geiger of SF’s Department of the Environment told us that the study, conducted under laboratory conditions, was not necessarily field-applicable.) But SFRPD is using two of the tested pesticides – Garlon and Imazapyr – on Twin Peaks. Is it worth it? We don’t know, but we can’t help wondering if Bermuda buttercups might be better for the butterflies than Garlon. (The study on metalmark butterflies and herbicides is here: Stark_2012 metalmark research)
WILL MORE BUTTERFLIES BE MOVED?
We’re not sure what happens next. It probably depends on whether the city or USFWS are willing to fund ongoing relocations of butterflies. It’s costly and labor-intensive. They need to avoid taking too many butterflies from any one place on any one day (which implies repeated visits), they need to transport them carefully and keep them under observation as they release them.
The Mission Blue Butterfly population on Twin Peaks is unlikely to be self-sustaining at present, though as the report points out, it has been proved that the butterfly can complete its life-cycle these. But that’s the barest standard of success. It’s barely hanging on. Can it thrive?
[EDITED TO ADD: UPDATE, JUNE 2013
There’s better news in 2013’s crop. They spotted the largest number of Mission Blue eggs ever: 1170 of them. They also saw 27 native-born adult butterflies, 6 females and 21 males, prior to moving in another 58 butterflies from San Bruno mountain – 38 females and 20 males.
It’s the most promising year thus far. It makes us wonder whether the dry winter had anything to do with it.
Here’s the updated graph.]