Mt. Davidson Question


Jim Chiropolos
 

I birded Mt. D for the first time ever earlier this week and can see why it is one if the top SF birding locations. What an interesting micro-climate  - half temperate rainforest and half chapperal. The temperate rainforest area is introduced eucalyptus forest  with a dense understory of non native blackberry.  My question- what was the habitat previous to 1850? And would it be as good for passerine migrants?

This is a good fog year and it was quite moist on Mt. D. I think about the sky islands I bird in the east bay - Vollmer peak and Mt. Diablo which are seriously affected by the drought and are missing breeding bird species this year as a result. I would guess Mt. D has not been affected as much by the drought.

Good Birding 
Jim Chiropolos 
East Bay


Eddie Bartley
 

Yo Jim, good to read from ya! In part here's a brief natural history on Mt. D> My question- what was the habitat previous to 1850? And would it be as good for passerine migrants?

 

SF hilltops in the 1850s were still primarily deep-rooted perennial native grasslands although annual grasses introduced from Europe (introduced with/for livestock food initially) would likely have been creeping in by then.

 

The Mega-faunal herbivores were long gone but large grazers like Tule Elk were present until about that time as well so they would have kept the scrub and trees down. Also, fire was reportedly used by Ramaytush-Ohlone to encourage grasslands. Must have been some incredible super-blooms in wet years. 

 

Beginning with the arrival of the Spanish and the axe, most of the ancient oak woodlands would have been cut by the 1850s and, with a quarter million people arriving, mostly camping, trees and scrub vegetation would have been chopped to heck and back and livestock numbers greatly increased. 

 

In the 1890's the SF Board of Supervisors passed a property tax-abatement law providing for tax-free land ownership if people forested the land they owned. Adolph Sutro, philanthropist and reluctant mayor at the time owned about 10% of all private lands in SF at the time. Following the Presidio military practices at the time (an effort to delineate Presidio Land from SF and add wind blocks) he planted the Blue Gums, along with some Cypress - real thick with a plan to thin them later which never happened as the money ran out. The basic idea was to quick-forest the land for future forest product but soon it was realized that Blue Gums aren't very good for that and it was impractical anyway. The trees add some inches of fog drip which the highly invasive Himalayan blackberry and ivy love, the latter of which is choking many of the Blue Gum out slowly. A few species of frugivorous thrushes, Junco, Song Sparrow and Pacific Wren like it just fine but breeding and migrant grassland birds naturally disappeared from the forested area - paralleling the decline of grassland birds continent wide. The trees provide structure for arboreal migrants and while Blue Gum support a paltry number of edible insects (5 to 7 lerp psyllids - compared to oaks - many hundreds), they attract insectivorous migrants and wintering Yellow-rumps amongst others - primarily along the edge habitat with the restored native understory (elderberry, berberis, sage, vaccinium, etc.) There are a few surviving but struggling rare native grassland plants too. 

As typical, most of the birds and especially the migrants are detected along the edges either at various levels of the Blue Gum and Cypress, or in the native understory
or moving back and forth depending on their various styles. Buntings and sparrows can be often be found in the eastern grassland/scrub interface in migration. Nuttall's White Crowns are now abundant breeders in the restored area.

For over 30 years members of CNPS Yerba Buena and Friend's of Mt. D have been volunteering with SF NRD to remove the mono-cultures of ivy and blackberry and plant native understory. It works really well and looks great but it takes constant defense from the primary invasives and the Blue Gum tree litter. It's difficult to say how much that restoration is affecting the bird demographics within the forest. It's still primarily blackberry and ivy at his point. The native Nootka reed-grass and nectar loving species love it though and respond favorably. Birds are often working right at our feet when we're clearing or planting. 

So I guess the short answer is a question, which passerines? Passage arboreal passerines probably stop more and linger longer, frugivorous birds benefit from blackberry and ivy food, understory passerines numbers, especially breeders are improving due to restorations, grassland passerines continue to decline. 

Eddie Bartley

 


 


Bob Hall
 

Good questions. As the eucalyptus plantation continues to age and die out the habitat will likely change. You can compare the eBird checklists from Mt. D’s sibling mountain, San Bruno Mountain. However, Mt. D. is a much smaller space due to development, so the lists would fall between the lists of San Bruno Mountain and the overly trounced Twin Peaks. Breeding birds and butterflies may fair better while migrants would lose out. So while birders would be ticked off about reduced checklist ticking, other species may benefit. San Bruno Mountain has rare and endangered flora and fauna, manzanitas and butterflies - lots of biodiversity - and Mt. D is always on the verge of becoming more and more homogenous with a handful of species dominating. Ground nesters would like the euke-less habitat in theory but we know people and their pets wouldn’t tolerate them. I guess that’s why migrants have an advantage of landing in the high treetops.

So as the eukes wane, should they be replaced with climate-adapted, climate storing, biodiversity powerhouses like oaks and grasslands? Or more exotics that might lure in a fleeting hungry nectar lover? We may be facing these decisions in our lifetime.

Bob Hall
SF

--
Bob Hall
San Francisco, CA
"There is no better high than discovery." - E.O. Wilson